René Descartes (1596—1650): Overview

descarteRené Descartes is often credited with being the "Father of
Modern Philosophy." This title is justified due both to his break with
the traditional Scholastic-Aristotelian philosophy prevalent at his
time and to his development and promotion of the new, mechanistic
sciences. His fundamental break with Scholastic philosophy was
twofold. First, Descartes thought that the Scholastics' method was
prone to doubt given their reliance on sensation as the source for all
knowledge. Second, he wanted to replace their final causal model of
scientific explanation with the more modern, mechanistic model.

Descartes attempted to address the former issue via his method of
doubt. His basic strategy was to consider false any belief that falls
prey to even the slightest doubt. This "hyperbolic doubt" then serves
to clear the way for what Descartes considers to be an unprejudiced
search for the truth. This clearing of his previously held beliefs
then puts him at an epistemological ground-zero. From here Descartes
sets out to find something that lies beyond all doubt. He eventually
discovers that "I exist" is impossible to doubt and is, therefore,
absolutely certain. It is from this point that Descartes proceeds to
demonstrate God's existence and that God cannot be a deceiver. This,
in turn, serves to fix the certainty of everything that is clearly and
distinctly understood and provides the epistemological foundation
Descartes set out to find.

Once this conclusion is reached, Descartes can proceed to rebuild his
system of previously dubious beliefs on this absolutely certain
foundation. These beliefs, which are re-established with absolute
certainty, include the existence of a world of bodies external to the
mind, the distinction of the immaterial mind from the body, and his
mechanistic model of physics based on the clear and distinct ideas of
geometry. This points toward his second, major break with the
Scholastic Aristotelian tradition in that Descartes intended to
replace their system based on final causal explanations with his
system based on mechanistic principles. Descartes also applied this
mechanistic framework to the operation of plant, animal and human
bodies, sensation and the passions. All of this eventually culminating
in a moral system based on the notion of "generosity."

The presentation below provides an overview of Descartes'
philosophical thought as it relates to these various metaphysical,
epistemological, religious, moral and scientific issues, covering the
wide range of his published works and correspondence.

1. Life

René Descartes was born to Joachim Descartes and Jeanne Brochard on
March 31, 1596 in La Haye, France near Tours. He was the youngest of
the couple's three surviving children. The oldest child, Pierre, died
soon after his birth on October 19, 1589. His sister, Jeanne, was
probably born sometime the following year, while his surviving older
brother, also named Pierre, was born on October 19, 1591. The
Descartes clan was a bourgeois family composed of mostly doctors and
some lawyers. Joachim Descartes fell into this latter category and
spent most of his career as a member of the provincial parliament.

After the death of their mother, which occurred soon after René's
birth, the three Descartes children were sent to their maternal
grandmother, Jeanne Sain, to be raised in La Haye and remained there
even after their father remarried in 1600. Not much is known about his
early childhood, but René is thought to have been a sickly and fragile
child, so much so that when he was sent to board at the Jesuit college
at La Fleche on Easter of 1607. There, René was not obligated to rise
at 5:00am with the other boys for morning prayers but was allowed to
rest until 10:00am mass. At La Fleche, Descartes completed the usual
courses of study in grammar and rhetoric and the philosophical
curriculum with courses in the "verbal arts" of grammar, rhetoric and
dialectic (or logic) and the "mathematical arts" comprised of
arithmetic, music, geometry and astronomy. The course of study was
capped off with courses in metaphysics, natural philosophy and ethics.
Descartes is known to have disdained the impractical subjects despite
having an affinity for the mathematical curriculum. But, all things
considered, he did receive a very broad liberal arts education before
leaving La Fleche in 1614.

Little is known of Descartes' life from 1614-1618. But what is known
is that during 1615-1616 he received a degree and a license in civil
and canon law at the University of Poiters. However, some speculate
that from 1614-1615 Descartes suffered a nervous breakdown in a house
outside of Paris and that he lived in Paris from 1616-1618. The story
picks up in the summer of 1618 when Descartes went to the Netherlands
to become a volunteer for the army of Maurice of Nassau. It was during
this time that he met Isaac Beekman, who was, perhaps, the most
important influence on his early adulthood. It was Beekman who
rekindled Descartes' interest in science and opened his eyes to the
possibility of applying mathematical techniques to other fields. As a
New Year's gift to Beekman, Descartes composed a treatise on music,
which was then considered a branch of mathematics, entitled Compendium
Musicae. In 1619 Descartes began serious work on mathematical and
mechanical problems under Beekman's guidance and, finally, left the
service of Maurice of Nassau, planning to travel through Germany to
join the army of Maximilian of Bavaria.

It is during this year (1619) that Descartes was stationed at Ulm and
had three dreams that inspired him to seek a new method for scientific
inquiry and to envisage a unified science. Soon afterwards, in 1620,
he began looking for this new method, starting but never completing
several works on method, including drafts of the first eleven rules of
Rules for the Direction of the Mind. Descartes worked on and off on it
for years until it was finally abandoned for good in 1628. During this
time, he also worked on other, more scientifically oriented projects
such as optics. In the course of these inquiries, it is possible that
he discovered the law of refraction as early as 1626. It is also
during this time that Descartes had regular contact with Father Marin
Mersenne, who was to become his long time friend and contact with the
intellectual community during his 20 years in the Netherlands.

Descartes moved to the Netherlands in late 1628 and, despite several
changes of address and a few trips back to France, he remained there
until moving to Sweden at the invitation of Queen Christina in late
1649. He moved to the Netherlands in order to achieve solitude and
quiet that he could not attain with all the distractions of Paris and
the constant intrusion of visitors. It is here in 1629 that Descartes
began work on "a little treatise," which took him approximately three
years to complete, entitled The World.. This work was intended to show
how mechanistic physics could explain the vast array of phenomena in
the world without reference to the Scholastic principles of
substantial forms and real qualities, while also asserting a
heliocentric conception of the solar system. But the condemnation of
Galileo by the Inquisition for maintaining this latter thesis led
Descartes to suppress its publication. From 1634-1636, Descartes
finished his scientific essays Dioptique and Meteors, which apply his
geometrical method to these fields. He also wrote a preface to these
essays in the winter of 1635/1636 to be attached to them in addition
to another one on geometry. This "preface" became The Discourse on
Method and was published in French along with the three essays in June
1637. And, on a personal note, during this time his daughter,
Francine, was born in 1635, her mother being a maid at the home where
Descartes was staying. But Francine, at the age of five, died of a
fever in 1640 when he was making arrangements for her to live with
relatives in France so as to ensure her education.

Descartes began work on Meditations on First Philosophy in 1639.
Through Mersenne, Descartes solicited criticism of his Meditations
from amongst the most learned people of his day, including Antoine
Arnauld, Peirre Gassendi, and Thomas Hobbes. The first edition of the
Meditations was published in Latin in 1641 with six sets of objections
and his replies. A second edition published in 1642 also included a
seventh set of objections and replies as well as a letter to Father
Dinet in which Descartes defended his system against charges of
unorthodoxy. These charges were raised at the Universities of Utrecht
and Leiden and stemmed from various misunderstandings about his method
and the supposed opposition of his theses to Aristotle and the
Christian faith.

This controversy led Descartes to post two open letters against his
enemies. The first is entitled Notes on a Program posted in 1642 in
which Descartes refutes the theses of his recently estranged disciple,
Henricus Regius, a professor of medicine at Utrecht. These Notes were
intended not only to refute what Descartes understood to be Regius'
false theses but also to distance himself from his former disciple,
who had started a ruckus at Utrecht by making unorthodox claims about
the nature of human beings. The second is a long attack directed at
the rector of Utrecht, Gisbertus Voetius in the Open Letter to
Voetiusposted in 1643. This was in response to a pamphlet anonymously
circulated by some of Voetius' friends at the University of Leiden
further attacking Descartes' philosophy. Descartes' Open Letter led
Voetius to have him summoned before the council of Utrecht, who
threatened him with expulsion and the public burning of his books.
Descartes, however, was able to flee to the Hague and convince the
Prince of Orange to intervene on his behalf.

In the following year (1643), Descartes began an affectionate and
philosophically fruitful correspondence with Princess Elizabeth of
Bohemia, who was known for her acute intellect and had read the
Discourse on Method. Yet, as this correspondence with Elizabeth was
beginning, Descartes was already in the midst of writing a textbook
version of his philosophy entitled Principles of Philosophy, which he
ultimately dedicated to her. Although it was originally supposed to
have six parts, he published it in 1644 with only four completed: The
Principles of Human Knowledge, The Principles of Material Things, The
Visible Universe, and The Earth. The other two parts were to be on
plant and animal life and on human beings, but he decided it would be
impossible for him to conduct all the experiments necessary for
writing them. Elizabeth probed Descartes about issues that he had not
dealt with in much detail before, including free will, the passions
and morals. This eventually inspired Descartes to write a treatise
entitled The Passions of the Soul, which was published just before his
departure to Sweden in 1649. Also, during these later years, the
Meditations and Principles were translated from Latin into French for
a wider, more popular audience and were published in 1647.

In late 1646, Queen Christina of Sweden initiated a correspondence
with Descartes through a French diplomat and friend of Descartes'
named Chanut. Christina pressed Descartes on moral issues and a
discussion of the absolute good. This correspondence eventually led to
an invitation for Descartes to join the Queen's court in Stockholm in
February 1649. Although he had his reservations about going, Descartes
finally accepted Christina's invitation in July of that year. He
arrived in Sweden in September 1649 where he was asked to rise at
5:00am to meet the Queen to discuss philosophy, contrary to his usual
habit, developed at La Fleche, of sleeping in late,. His decision to
go to Sweden, however, was ill-fated, for Descartes caught pneumonia
and died on February 11, 1650.
2. The Modern Turn
a. Against Scholasticism

Descartes is often called the "Father of Modern Philosophy," implying
that he provided the seed for a new philosophy that broke away from
the old in important ways. This "old" philosophy is Aristotle's as it
was appropriated and interpreted throughout the later medieval period.
In fact, Aristotelianism was so entrenched in the intellectual
institutions of Descartes' time that commentators argued that evidence
for its the truth could be found in the Bible. Accordingly, if someone
were to try to refute some main Aristotelian tenet, then he could be
accused of holding a position contrary to the word of God and be
punished. However, by Descartes' time, many had come out in some way
against one Scholastic-Aristotelian thesis or other. So, when
Descartes argued for the implementation of his modern system of
philosophy, breaks with the Scholastic tradition were not
unprecedented.

Descartes broke with this tradition in at least two fundamental ways.
The first was his rejection of substantial forms as explanatory
principles in physics. A substantial form was thought to be an
immaterial principle of material organization that resulted in a
particular thing of a certain kind. The main principle of substantial
forms was the final cause or purpose of being that kind of thing. For
example, the bird called the swallow. The substantial form of
"swallowness" unites with matter so as to organize it for the sake of
being a swallow kind of thing. This also means that any dispositions
or faculties the swallow has by virtue of being that kind of thing is
ultimately explained by the goal or final cause of being a swallow.
So, for instance, the goal of being a swallow is the cause of the
swallow's ability to fly. Hence, on this account, a swallow flies for
the sake of being a swallow. Although this might be true, it does not
say anything new or useful about swallows, and so it seemed to
Descartes that Scholastic philosophy and science was incapable of
discovering any new or useful knowledge.

Descartes rejected the use of substantial forms and their concomitant
final causes in physics precisely for this reason. Indeed, his essay
Meteorology, that appeared alongside the Discourse on Method, was
intended to show that clearer and more fruitful explanations can be
obtained without reference to substantial forms but only by way of
deductions from the configuration and motion of parts. Hence, his
point was to show that mechanistic principles are better suited for
making progress in the physical sciences. Another reason Descartes
rejected substantial forms and final causes in physics was his belief
that these notions were the result of the confusion of the idea of the
body with that of the mind. In theSixth Replies, Descartes uses the
Scholastic conception of gravity in a stone, to make his point. On
this account, a characteristic goal of being a stone was a tendency to
move toward the center of the earth. This explanation implies that the
stone has knowledge of this goal, of the center of the earth and of
how to get there. But how can a stone know anything, since it does not
think? So, it is a mistake to ascribe mental properties like knowledge
to entirely physical things. This mistake should be avoided by clearly
distinguishing the idea of the mind from the idea of the body.
Descartes considered himself to be the first to do this. His expulsion
of the metaphysical principles of substantial forms and final causes
helped clear the way for Descartes' new metaphysical principles on
which his modern, mechanistic physics was based.

The second fundamental point of difference Descartes had with the
Scholastics was his denial of the thesis that all knowledge must come
from sensation. The Scholastics were devoted to the Aristotelian tenet
that everyone is born with a clean slate, and that all material for
intellectual understanding must be provided through sensation.
Descartes, however, argued that since the senses sometimes deceive,
they cannot be a reliable source for knowledge. Furthermore, the truth
of propositions based on sensation is naturally probabilistic and the
propositions, therefore, are doubtful premises when used in arguments.
Descartes was deeply dissatisfied with such uncertain knowledge. He
then replaced the uncertain premises derived from sensation with the
absolute certainty of the clear and distinct ideas perceived by the
mind alone, as will be explained below.
b. Descartes' Project

In the preface to the French edition of the Principles of Philosophy,
Descartes uses a tree as a metaphor for his holistic view of
philosophy. "The roots are metaphysics, the trunk is physics, and the
branches emerging from the trunk are all the other sciences, which may
be reduced to three principal ones, namely medicine, mechanics and
morals" (AT IXB 14: CSM I 186). Although Descartes does not expand
much more on this image, a few other insights into his overall project
can be discerned. First, notice that metaphysics constitutes the roots
securing the rest of the tree. For it is in Descartes' metaphysics
where an absolutely certain and secure epistemological foundation is
discovered. This, in turn, grounds knowledge of the geometrical
properties of bodies, which is the basis for his physics. Second,
physics constitutes the trunk of the tree, which grows up directly
from the roots and provides the basis for the rest of the sciences.
Third, the sciences of medicine, mechanics and morals grow out of the
trunk of physics, which implies that these other sciences are just
applications of his mechanistic science to particular subject areas.
Finally, the fruits of the philosophy tree are mainly found on these
three branches, which are the sciences most useful and beneficial to
humankind. However, an endeavor this grand cannot be conducted
haphazardly but should be carried out in an orderly and systematic
way. Hence, before even attempting to plant this tree, Descartes must
first figure out a method for doing so.
3. Method

Aristotle and subsequent medieval dialecticians set out a fairly
large, though limited, set of acceptable argument forms known as
"syllogisms" composed of a general or major premise, a particular or
minor premise and a conclusion. Although Descartes recognized that
these syllogistic forms preserve truth from premises to conclusion
such that if the premises are true, then the conclusion must be true,
he still found them faulty. First, these premises are supposed to be
known when, in fact, they are merely believed, since they express only
probabilities based on sensation. Accordingly, conclusions derived
from merely probable premises can only be probable themselves, and,
therefore, these probable syllogisms serve more to increase doubt
rather than knowledge Moreover, the employment of this method by those
steeped in the Scholastic tradition had led to such subtle conjectures
and plausible arguments that counter-arguments were easily
constructed, leading to profound confusion. As a result, the
Scholastic tradition had become such a confusing web of arguments,
counter-arguments and subtle distinctions that the truth often got
lost in the cracks. (Rules for the Direction of the Mind, AT X 364,
405-406 & 430: CSM I 11-12, 36 & 51-52).

Descartes sought to avoid these difficulties through the clarity and
absolute certainty of geometrical-style demonstration. In geometry,
theorems are deduced from a set of self-evident axioms and universally
agreed upon definitions. Accordingly, direct apprehension of clear,
simple and indubitable truths (or axioms) by intuition and deductions
from those truths can lead to new and indubitable knowledge. Descartes
found this promising for several reasons. First, the ideas of geometry
are clear and distinct, and therefore they are easily understood
unlike the confused and obscure ideas of sensation. Second, the
propositions constituting geometrical demonstrations are not
probabilistic conjectures but are absolutely certain so as to be
immune from doubt. This has the additional advantage that any
proposition derived from some one or combination of these absolutely
certain truths will itself be absolutely certain. Hence, geometry's
rules of inference preserve absolutely certain truth from simple,
indubitable and intuitively grasped axioms to their deductive
consequences unlike the probable syllogisms of the Scholastics.

The choice of geometrical method was obvious for Descartes given his
previous success in applying this method to other disciplines like
optics. Yet his application of this method to philosophy was not
unproblematic due to a revival of ancient arguments for global or
radical skepticism based on the doubtfulness of human reasoning. But
Descartes wanted to show that truths both intuitively grasped and
deduced are beyond this possibility of doubt. His tactic was to show
that, despite the best skeptical arguments, there is at least one
intuitive truth that is beyond all doubt and from which the rest of
human knowledge can be deduced. This is precisely the project of
Descartes' seminal work, Meditations on First Philosophy.

In the First Meditation, Descartes lays out several arguments for
doubting all of his previously held beliefs. He first observes that
the senses sometimes deceive, for example, objects at a distance
appear to be quite small, and surely it is not prudent to trust
someone (or something) that has deceived us even once. However,
although this may apply to sensations derived under certain
circumstances, doesn't it seem certain that "I am here, sitting by the
fire, wearing a winter dressing gown, holding this piece of paper in
my hands, and so on"? (AT VII 18: CSM II 13). Descartes' point is that
even though the senses deceive us some of the time, what basis for
doubt exists for the immediate belief that, for example, you are
reading this article? But maybe the belief of reading this article or
of sitting by the fireplace is not based on true sensations at all but
on the false sensations found in dreams. If such sensations are just
dreams, then it is not really the case that you are reading this
article but in fact you are in bed asleep. Since there is no
principled way of distinguishing waking life from dreams, any belief
based on sensation has been shown to be doubtful. This includes not
only the mundane beliefs about reading articles or sitting by the fire
but even the beliefs of experimental science are doubtful, because the
observations upon which they are based may not be true but mere dream
images. Therefore, all beliefs based on sensation have been called
into doubt, because it might all be a dream.

This, however, does not pertain to mathematical beliefs, since they
are not based on sensation but on reason. For even though one is
dreaming, for example, that, 2 + 3 = 5, the certainty of this
proposition is not called into doubt, because 2 + 3 = 5 whether the
one believing it is awake or dreaming. Descartes continues to wonder
about whether or not God could make him believe there is an earth, sky
and other extended things when, in fact, these things do not exist at
all. In fact, people sometimes make mistakes about things they think
are most certain such as mathematical calculations. But maybe people
are not mistaken just some of the time but all of the time such that
believing that 2 + 3 = 5 is some kind of persistent and collective
mistake, and so the sum of 2 + 3 is really something other than 5.
However, such universal deception seems inconsistent with God's
supreme goodness. Indeed, even the occasional deception of
mathematical miscalculation also seems inconsistent with God's
goodness, yet people do sometimes make mistakes. Then, in line with
the skeptics, Descartes supposes, for the sake of his method, that God
does not exist, but instead there is an evil demon with supreme power
and cunning that puts all his efforts into deceiving him so that he is
always mistaken about everything, including mathematics.

In this way, Descartes called all of his previous beliefs into doubt
through some of the best skeptical arguments of his day But he was
still not satisfied and decided to go a step further by considering
false any belief that falls prey to even the slightest doubt. So, by
the end of the First Meditation, Descartes finds himself in a
whirlpool of false beliefs. However, it is important to realize that
these doubts and the supposed falsehood of all his beliefs are for the
sake of his method: he does not really believe that he is dreaming or
is being deceived by an evil demon; he recognizes that his doubt is
merely hyperbolic. But the point of this "methodological" or
'hyperbolic" doubt is to clear the mind of preconceived opinions that
might obscure the truth. The goal then is to find something that
cannot be doubted even though an evil demon is deceiving him and even
though he is dreaming. This first indubitable truth will then serve as
an intuitively grasped metaphysical "axiom" from which absolutely
certain knowledge can be deduced. For more, see Cartesian skepticism.
4. The Mind
a. Cogito, ergo sum

In the Second Meditation, Descartes tries to establish absolute
certainty in his famous reasoning: Cogito, ergo sum or "I think,
therefore I am." These Meditations are conducted from the first person
perspective, from Descartes.' However, he expects his reader to
meditate along with him to see how his conclusions were reached. This
is especially important in the Second Meditation where the intuitively
grasped truth of "I exist" occurs. So the discussion here of this
truth will take place from the first person or "I" perspective. All
sensory beliefs had been found doubtful in the previous meditation,
and therefore all such beliefs are now considered false. This includes
the belief that I have a body endowed with sense organs. But does the
supposed falsehood of this belief mean that I do not exist? No, for if
I convinced myself that my beliefs are false, then surely there must
be an "I" that was convinced. Moreover, even if I am being deceived by
an evil demon, I must exist in order to be deceived at all. So "I must
finally conclude that the proposition, 'I am,' 'I exist,' is
necessarily true whenever it is put forward by me or conceived in my
mind" (AT VII 25: CSM II 16-17). This just means that the mere fact
that I am thinking, regardless of whether or not what I am thinking is
true or false, implies that there must be something engaged in that
activity, namely an "I." Hence, "I exist" is an indubitable and,
therefore, absolutely certain belief that serves as an axiom from
which other, absolutely certain truths can be deduced.
b. The Nature of the Mind and its Ideas

The Second Meditation continues with Descartes asking, "What am I?"
After discarding the traditional Scholastic-Aristotelian concept of a
human being as a rational animal due to the inherent difficulties of
defining "rational" and "animal," he finally concludes that he is a
thinking thing, a mind: "A thing that doubts, understands, affirms,
denies, is willing, is unwilling, and also imagines and has sense
perceptions" (AT VII 28: CSM II 19). In the Principles, part I,
sections 32 and 48, Descartes distinguishes intellectual perception
and volition as what properly belongs to the nature of the mind alone
while imagination and sensation are, in some sense, faculties of the
mind insofar as it is united with a body. So imagination and sensation
are faculties of the mind in a weaker sense than intellect and will,
since they require a body in order to perform their functions.
Finally, in the Sixth Meditation, Descartes claims that the mind or
"I" is a non-extended thing. Now, since extension is the nature of
body, is a necessary feature of body, it follows that the mind is by
its nature not a body but an immaterial thing. Therefore, what I am is
an immaterial thinking thing with the faculties of intellect and will.

It is also important to notice that the mind is a substance and the
modes of a thinking substance are its ideas. For Descartes a substance
is a thing requiring nothing else in order to exist. Strictly
speaking, this applies only to God whose existence is his essence, but
the term "substance" can be applied to creatures in a qualified sense.
Minds are substances in that they require nothing except God's
concurrence, in order to exist. But ideas are "modes" or "ways" of
thinking, and, therefore, modes are not substances, since they must be
the ideas of some mind or other. So, ideas require, in addition to
God's concurrence, some created thinking substance in order to exist
(see Principles of Philosophy, part I, sections 51 & 52). Hence the
mind is an immaterial thinking substance, while its ideas are its
modes or ways of thinking.

Descartes continues on to distinguish three kinds of ideas at the
beginning of the Third Meditation, namely those that are fabricated,
adventitious, or innate. Fabricated ideas are mere inventions of the
mind. Accordingly, the mind can control them so that they can be
examined and set aside at will and their internal content can be
changed. Adventitious ideas are sensations produced by some material
thing existing externally to the mind. But, unlike fabrications,
adventitious ideas cannot be examined and set aside at will nor can
their internal content be manipulated by the mind. For example, no
matter how hard one tries, if someone is standing next to a fire, she
cannot help but feel the heat as heat. She cannot set aside the
sensory idea of heat by merely willing it as we can do with our idea
of Santa Claus, for example. She also cannot change its internal
content so as to feel something other than heat–say, cold. Finally,
innate ideas are placed in the mind by God at creation. These ideas
can be examined and set aside at will but their internal content
cannot be manipulated. Geometrical ideas are paradigm examples of
innate ideas. For example, the idea of a triangle can be examined and
set aside at will, but its internal content cannot be manipulated so
as to cease being the idea of a three-sided figure. Other examples of
innate ideas would be metaphysical principles like "what is done
cannot be undone," the idea of the mind, and the idea of God.

Descartes' idea of God will be discussed momentarily, but let's
consider his claim that the mind is better known than the body. This
is the main point of the wax example found in the Second Meditation.
Here, Descartes pauses from his methodological doubt to examine a
particular piece of wax fresh from the honeycomb:

It has not yet quite lost the taste of the honey; it retains some
of the scent of flowers from which it was gathered; its color shape
and size are plain to see; it is hard, cold and can be handled without
difficulty; if you rap it with your knuckle it makes a sound. (AT VII
30: CSM II 20)

The point is that the senses perceive certain qualities of the wax
like its hardness, smell, and so forth. But, as it is moved closer to
the fire, all of these sensible qualities change. "Look: the residual
taste is eliminated, the smell goes away, the color changes, the shape
is lost, the size increases, it becomes liquid and hot" (AT VII 30:
CSM II 20). However, despite these changes in what the senses perceive
of the wax, it is still judged to be the same wax now as before. To
warrant this judgment, something that does not change must have been
perceived in the wax.

This reasoning establishes at least three important points. First, all
sensation involves some sort of judgment, which is a mental mode.
Accordingly, every sensation is, in some sense, a mental mode, and
"the more attributes [that is, modes] we discover in the same thing or
substance, the clearer is our knowledge of that substance" (AT VIIIA
8: CSM I 196). Based on this principle, the mind is better known than
the body, because it has ideas about both extended and mental things
and not just of extended things, and so it has discovered more modes
in itself than in bodily substances. Second, this is also supposed to
show that what is unchangeable in the wax is its extension in length,
breadth and depth, which is not perceivable by the senses but by the
mind alone. The shape and size of the wax are modes of this extension
and can, therefore, change. But the extension constituting this wax
remains the same and permits the judgment that the body with the modes
existing in it after being moved by the fire is the same body as
before even though all of its sensible qualities have changed. One
final lesson is that Descartes is attempting to wean his reader from
reliance on sense images as a source for, or an aid to, knowledge.
Instead, people should become accustomed to thinking without images in
order to clearly understand things not readily or accurately
represented by them, for example, God and the mind. So, according to
Descartes, immaterial, mental things are better known and, therefore,
are better sources of knowledge than extended things.
5. God
a. The Causal Arguments

At the beginning of the Third Meditation only "I exist" and "I am a
thinking thing" are beyond doubt and are, therefore, absolutely
certain. From these intuitively grasped, absolutely certain truths,
Descartes now goes on to deduce the existence of something other than
himself, namely God. Descartes begins by considering what is necessary
for something to be the adequate cause of its effect. This will be
called the "Causal Adequacy Principle" and is expressed as follows:
"there must be at least as much reality in the efficient and total
cause as in the effect of that cause," which in turn implies that
something cannot come from nothing (AT VII 40: CSM II 28). Here
Descartes is espousing a causal theory that implies whatever is
possessed by an effect must have been given to it by its cause. For
example, when a pot of water is heated to a boil, it must have
received that heat from some cause that had at least that much heat.
Moreover, something that is not hot enough cannot cause water to boil,
because it does not have the requisite reality to bring about that
effect. In other words, something cannot give what it does not have.

Descartes goes on to apply this principle to the cause of his ideas.
This version of the Causal Adequacy Principle states that whatever is
contained objectively in an idea must be contained either formally or
eminently in the cause of that idea. Definitions of some key terms are
now in order. First, the objective reality contained in an idea is
just its representational content; in other words, it is the "object"
of the idea or what that idea is about. The idea of the sun, for
instance, contains the reality of the sun in it objectively. Second,
the formal reality contained in something is a reality actually
contained in that thing. For example, the sun itself has the formal
reality of extension since it is actually an extended thing or body.
Finally, a reality is contained in something eminently when that
reality is contained in it in a higher form such that (1) the thing
does not possess that reality formally, but (2) it has the ability to
cause that reality formally in something else. For example, God is not
formally an extended thing but solely a thinking thing; however, he is
eminently the extended universe in that it exists in him in a higher
form, and accordingly he has the ability to cause its existence. The
main point is that the Causal Adequacy Principle also pertains to the
causes of ideas so that, for instance, the idea of the sun must be
caused by something that contains the reality of the sun either
actually (formally) or in some higher form (eminently).

Once this principle is established, Descartes looks for an idea of
which he could not be the cause. Based on this principle, he can be
the cause of the objective reality of any idea that he has either
formally or eminently. He is formally a finite substance, and so he
can be the cause of any idea with the objective reality of a finite
substance. Moreover, since finite substances require only God's
concurrence to exist and modes require a finite substance and God,
finite substances are more real than modes. Accordingly, a finite
substance is not formally but eminently a mode, and so he can be the
cause of all his ideas of modes. But the idea of God is the idea of an
infinite substance. Since a finite substance is less real than an
infinite substance by virtue of the latter's absolute independence, it
follows that Descartes, a finite substance, cannot be the cause of his
idea of an infinite substance. This is because a finite substance does
not have enough reality to be the cause of this idea, for if a finite
substance were the cause of this idea, then where would it have gotten
the extra reality? But the idea must have come from something. So
something that is actually an infinite substance, namely God, must be
the cause of the idea of an infinite substance. Therefore, God exists
as the only possible cause of this idea.

Notice that in this argument Descartes makes a direct inference from
having the idea of an infinite substance to the actual existence of
God. He provides another argument that is cosmological in nature in
response to a possible objection to this first argument. This
objection is that the cause of a finite substance with the idea of God
could also be a finite substance with the idea of God. Yet what was
the cause of that finite substance with the idea of God? Well, another
finite substance with the idea of God. But what was the cause of that
finite substance with the idea of God? Well, another finite substance
. . . and so on to infinity. Eventually an ultimate cause of the idea
of God must be reached in order to provide an adequate explanation of
its existence in the first place and thereby stop the infinite
regress. That ultimate cause must be God, because only he has enough
reality to cause it. So, in the end, Descartes claims to have deduced
God's existence from the intuitions of his own existence as a finite
substance with the idea of God and the Causal Adequacy Principle,
which is "manifest by the natural light," thereby indicating that it
is supposed to be an absolutely certain intuition as well.
b. The Ontological Argument

The ontological argument is found in the Fifth Meditation and follows
a more straightforwardly geometrical line of reasoning. Here Descartes
argues that God's existence is deducible from the idea of his nature
just as the fact that the sum of the interior angles of a triangle are
equal to two right angles is deducible from the idea of the nature of
a triangle. The point is that this property is contained in the nature
of a triangle, and so it is inseparable from that nature. Accordingly,
the nature of a triangle without this property is unintelligible.
Similarly, it is apparent that the idea of God is that of a supremely
perfect being, that is, a being with all perfections to the highest
degree. Moreover, actual existence is a perfection, at least insofar
as most would agree that it is better to actually exist than not. Now,
if the idea of God did not contain actual existence, then it would
lack a perfection. Accordingly, it would no longer be the idea of a
supremely perfect being but the idea of something with an
imperfection, namely non-existence, and, therefore, it would no longer
be the idea of God. Hence, the idea of a supremely perfect being or
God without existence is unintelligible. This means that existence is
contained in the essence of an infinite substance, and therefore God
must exist by his very nature. Indeed, any attempt to conceive of God
as not existing would be like trying to conceive of a mountain without
a valley – it just cannot be done.
6. The Epistemological Foundation
a. Absolute Certainty and the Cartesian Circle

Recall that in the First Meditation Descartes supposed that an evil
demon was deceiving him. So as long as this supposition remains in
place, there is no hope of gaining any absolutely certain knowledge.
But he was able to demonstrate God's existence from intuitively
grasped premises, thereby providing, a glimmer of hope of extricating
himself from the evil demon scenario. The next step is to demonstrate
that God cannot be a deceiver. At the beginning of the Fourth
Meditation, Descartes claims that the will to deceive is "undoubtedly
evidence of malice or weakness" so as to be an imperfection. But,
since God has all perfections and no imperfections, it follows that
God cannot be a deceiver. For to conceive of God with the will to
deceive would be to conceive him to be both having no imperfections
and having one imperfection, which is impossible; it would be like
trying to conceive of a mountain without a valley. This conclusion, in
addition to God's existence, provides the absolutely certain
foundation Descartes was seeking from the outset of the Meditations.
It is absolutely certain because both conclusions (namely that God
exists and that God cannot be a deceiver) have themselves been
demonstrated from immediately grasped and absolutely certain intuitive
truths.

This means that God cannot be the cause of human error, since he did
not create humans with a faculty for generating them, nor could God
create some being, like an evil demon, who is bent on deception.
Rather, humans are the cause of their own errors when they do not use
their faculty of judgment correctly. Second, God's non-deceiving
nature also serves to guarantee the truth of all clear and distinct
ideas. So God would be a deceiver, if there were a clear and distinct
idea that was false, since the mind cannot help but believe them to be
true. Hence, clear and distinct ideas must be true on pain of
contradiction. This also implies that knowledge of God's existence is
required for having any absolutely certain knowledge. Accordingly,
atheists, who are ignorant of God's existence, cannot have absolutely
certain knowledge of any kind, including scientific knowledge.

But this veridical guarantee gives rise to a serious problem within
the Meditations, stemming from the claim that all clear and distinct
ideas are ultimately guaranteed by God's existence, which is not
established until the Third Meditation. This means that those truths
reached in the Second Meditation, such as "I exist" and "I am a
thinking thing," and those principles used in the Third Meditation to
conclude that God exists, are not clearly and distinctly understood,
and so they cannot be absolutely certain. Hence, since the premises of
the argument for God's existence are not absolutely certain, the
conclusion that God exists cannot be certain either. This is what is
known as the "Cartesian Circle," because Descartes' reasoning seems to
go in a circle in that he needs God's existence for the absolute
certainty of the earlier truths and yet he needs the absolute
certainty of these earlier truths to demonstrate God's existence with
absolute certainty.

Descartes' response to this concern is found in the Second Replies.
There he argues that God's veridical guarantee only pertains to the
recollection of arguments and not the immediate awaRenéss of an
argument's clarity and distinctness currently under consideration.
Hence, those truths reached before the demonstration of God's
existence are clear and distinct when they are being attended to but
cannot be relied upon as absolutely certain when those arguments are
recalled later on. But once God's existence has been demonstrated, the
recollection of the clear and distinct perception of the premises is
sufficient for absolutely certain and, therefore, perfect knowledge of
its conclusion (see also the Fifth Meditation at AT VII 69-70: CSM II
XXX).
b. How to Avoid Error

In the Third Meditation, Descartes argues that only those ideas called
"judgments" can, strictly speaking, be true or false, because it is
only in making a judgment that the resemblance, conformity or
correspondence of the idea to things themselves is affirmed or denied.
So if one affirms that an idea corresponds to a thing itself when it
really does not, then an error has occurred. This faculty of judging
is described in more detail in the Fourth Meditation. Here judgment is
described as a faculty of the mind resulting from the interaction of
the faculties of intellect and will. Here Descartes observes that the
intellect is finite in that humans do not know everything, and so
their understanding of things is limited. But the will or faculty of
choice is seemingly infinite in that it can be applied to just about
anything whatsoever. The finitude of the intellect along with this
seeming infinitude of the will is the source of human error. For
errors arise when the will exceeds the understanding such that
something laying beyond the limits of the understanding is voluntarily
affirmed or denied. To put it more simply: people make mistakes when
they choose to pass judgment on things they do not fully understand.
So the will should be restrained within the bounds of what the mind
understands in order to avoid error. Indeed, Descartes maintains that
judgments should only be made about things that are clearly and
distinctly understood, since their truth is guaranteed by God's
non-deceiving nature. If one only makes judgments about what is
clearly and distinctly understood and abstains from making judgments
about things that are not, then error would be avoided altogether. In
fact, it would be impossible to go wrong if this rule were
unwaveringly followed.
7. Mind-Body Relation
a. The Real Distinction

One of Descartes' main conclusions is that the mind is really distinct
from the body. But what is a "real distinction"? Descartes explains it
best at Principles, part 1, section 60. Here he first states that it
is a distinction between two or more substances. Second, a real
distinction is perceived when one substance can be clearly and
distinctly understood without the other and vice versa. Third, this
clear and distinct understanding shows that God can bring about
anything understood in this way. Hence, in arguing for the real
distinction between mind and body, Descartes is arguing that 1) the
mind is a substance, 2) it can be clearly and distinctly understood
without any other substance, including bodies, and 3) that God could
create a mental substance all by itself without any other created
substance. So Descartes is ultimately arguing for the possibility of
minds or souls existing without bodies.

Descartes argues that mind and body are really distinct in two places
in the Sixth Meditation. The first argument is that he has a clear and
distinct understanding of the mind as a thinking, non-extended thing
and of the body as an extended, non-thinking thing. So these
respective ideas are clearly and distinctly understood to be opposite
from one another and, therefore, each can be understood all by itself
without the other. Two points should be mentioned here. First,
Descartes' claim that these perceptions are clear and distinct
indicates that the mind cannot help but believe them true, and so they
must be true for otherwise God would be a deceiver, which is
impossible. So the premises of this argument are firmly rooted in his
foundation for absolutely certain knowledge. Second, this indicates
further that he knows that God can create mind and body in the way
that they are being clearly and distinctly understood. Therefore, the
mind can exist without the body and vice versa.

The second version is found later in the Sixth Meditation where
Descartes claims to understand the nature of body or extension to be
divisible into parts, while the nature of the mind is understood to be
"something quite simple and complete" so as not to be composed of
parts and is, therefore, indivisible. From this it follows that mind
and body cannot have the same nature, for if this were true, then the
same thing would be both divisible and not divisible, which is
impossible. Hence, mind and body must have two completely different
natures in order for each to be able to be understood all by itself
without the other. Although Descartes does not make the further
inference here to the conclusion that mind and body are two really
distinct substances, it nevertheless follows from their respective
abilities to be clearly and distinctly understood without each other
that God could create one without the other.
b. The Mind-Body Problem

The famous mind-body problem has its origins in Descartes' conclusion
that mind and body are really distinct. The crux of the difficulty
lies in the claim that the respective natures of mind and body are
completely different and, in some way, opposite from one another. On
this account, the mind is an entirely immaterial thing without any
extension in it whatsoever; and, conversely, the body is an entirely
material thing without any thinking in it at all. This also means that
each substance can have only its kind of modes. For instance, the mind
can only have modes of understanding, will and, in some sense,
sensation, while the body can only have modes of size, shape, motion,
and quantity. But bodies cannot have modes of understanding or
willing, since these are not ways of being extended; and minds cannot
have modes of shape or motion, since these are not ways of thinking.

The difficulty arises when it is noticed that sometimes the will moves
the body, for example, the intention to ask a question in class causes
the raising of your arm, and certain motions in the body cause the
mind to have sensations. But how can two substances with completely
different natures causally interact? Pierre Gassendi in the Fifth
Objections and Princess Elizabeth in her correspondence with Descartes
both noted this problem and explained it in terms of contact and
motion. The main thrust of their concern is that the mind must be able
to come into contact with the body in order to cause it to move. Yet
contact must occur between two or more surfaces, and, since having a
surface is a mode of extension, minds cannot have surfaces. Therefore,
minds cannot come into contact with bodies in order to cause some of
their limbs to move. Furthermore, although Gassendi and Elizabeth were
concerned with how a mental substance can cause motion in a bodily
substance, a similar problem can be found going the other way: how can
the motion of particles in the eye, for example, traveling through the
optic nerve to the brain cause visual sensations in the mind, if no
contact or transfer of motion is possible between the two?

This could be a serious problem for Descartes, because the actual
existence of modes of sensation and voluntary bodily movement
indicates that mind and body do causally interact. But the completely
different natures of mind and body seem to preclude the possibility of
this interaction. Hence, if this problem cannot be resolved, then it
could be used to imply that mind and body are not completely different
but they must have something in common in order to facilitate this
interaction. Given Elizabeth's and Gassendi's concerns, it would
suggest that the mind is an extended thing capable of having a surface
and motion. Therefore, Descartes could not really come to a clear and
distinct understanding of mind and body independently of one another,
because the nature of the mind would have to include extension or body
in it.

Descartes, however, never seemed very concerned about this problem.
The reason for this lack of concern is his conviction expressed to
both Gassendi and Elizabeth that the problem rests upon a
misunderstanding about the union between mind and body. Though he does
not elaborate to Gassendi, Descartes does provide some insight in a 21
May 1643 letter to Elizabeth. In that letter, Descartes distinguishes
between various primitive notions. The first is the notion of the
body, which entails the notions of shape and motion. The second is the
notion of the mind or soul, which includes the perceptions of the
intellect and the inclinations of the will. The third is the notion of
the union of the soul with the body, on which depend the notion of the
soul's power to move the body and the body's power to cause sensations
and passions in the soul.

The notions entailed by or included in the primitive notions of body
and soul just are the notions of their respective modes. This suggests
that the notions depending on the primitive notion of the union of
soul and body are the modes of the entity resulting from this union.
This would also mean that a human being is one thing instead of two
things that causally interact through contact and motion as Elizabeth
and Gassendi supposed. Instead, a human being, that is, a soul united
with a body, would be a whole that is more than the sum of its parts.
Accordingly, the mind or soul is a part with its own capacity for
modes of intellect and will; the body is a part with its own capacity
for modes of size, shape, motion and quantity; and the union of mind
and body or human being, has a capacity for its own set of modes over
and above the capacities possessed by the parts alone. On this
account, modes of voluntary bodily movement would not be modes of the
body alone resulting from its mechanistic causal interaction with a
mental substance, but rather they would be modes of the whole human
being. The explanation of, for example, raising the arm would be found
in a principle of choice internal to human nature and similarly
sensations would be modes of the whole human being. Hence, the human
being would be causing itself to move and would have sensations and,
therefore, the problem of causal interaction between mind and body is
avoided altogether. Finally, on the account sketched here, Descartes'
human being is actually one, whole thing, while mind and body are its
parts that God could make exist independently of one another.

However, a final point should be made before closing this section. The
position sketched in the previous couple of paragraphs is not the
prevalent view among scholars and requires more justification than can
be provided here. Most scholars understand Descartes' doctrine of the
real distinction between mind and body in much the same way as
Elizabeth and Gassendi did such that Descartes' human being is
believed to be not one, whole thing but two substances that somehow
mechanistically interact. This also means that they find the mind-body
problem to be a serious, if not fatal, flaw of Descartes' entire
philosophy. But the benefit of the brief account provided here is that
it helps explain Descartes' lack of concern for this issue and his
persistent claims that an understanding of the union of mind and body
would put to rest people's concerns about causal interaction via
contact and motion.
8. Body and the Physical Sciences
a. Existence of the External World

In the Sixth Meditation, Descartes recognizes that sensation is a
passive faculty that receives sensory ideas from something else. But
what is this "something else"? According to the Causal Adequacy
Principle of the Third Meditation, this cause must have at least as
much reality either formally or eminently as is contained objectively
in the produced sensory idea. It, therefore, must be either Descartes
himself, a body or extended thing that actually has what is contained
objectively in the sensory idea, or God or some creature more noble
than a body, who would possess that reality eminently. It cannot be
Descartes, since he has no control over these ideas. It cannot be God
or some other creature more noble than a body, for if this were so,
then God would be a deceiver, because the very strong inclination to
believe that bodies are the cause of sensory ideas would then be
wrong; and if it is wrong, there is no faculty that could discover the
error. Accordingly, God would be the source of the mistake and not
human beings, which means that he would be a deceiver. So bodies must
be the cause of the ideas of them, and therefore bodies exist
externally to the mind.
b. The Nature of Body

In part II of the Principles, Descartes argues that the entire
physical universe is corporeal substance indefinitely extended in
length, breadth, and depth. This means that the extension constituting
bodies and the extension constituting the space in which those bodies
are said to be located are the same. Here Descartes is rejecting the
claim held by some that bodies have something over and above extension
as part of their nature, namely impenetrability, while space is just
penetrable extension in which impenetrable bodies are located.
Therefore, body and space have the same extension in that body is not
impenetrable extension and space penetrable extension, but rather
there is only one kind of extension. Descartes maintains further that
extension entails impenetrability, and hence there is only
impenetrable extension. He goes on to state that: "The terms 'place'
and 'space,' then, do not signify anything different from the body
which is said to be in a place . . ." (AT VIIIA 47: CSM I 228). Hence,
it is not that bodies are in space but that the extended universe is
composed of a plurality or plenum of impenetrable bodies. On this
account, there is no place in which a particular body is located, but
rather what is called a "place" is just a particular body's relation
to other bodies. However, when a body is said to change its place, it
merely has changed its relation to these other bodies, but it does not
leave an "empty" space behind to be filled by another body. Rather,
another body takes the place of the first such that a new part of
extension now constitutes that place or space.

Here an example should prove helpful. Consider the example of a full
wine bottle. The wine is said to occupy that place within the bottle.
Once the wine is finished, this place is now constituted by the
quantity of air now occupying it. Notice that the extension of the
wine and that of the air are two different sets of bodies, and so the
place inside the wine bottle was constituted by two different pieces
of extension. But, since these two pieces of extension have the same
size, shape and relation to the body surrounding it, that is, the
bottle, it is called one and the same "place" even though, strictly
speaking, it is made up of two different pieces of extension.
Therefore, so long as bodies of the same shape, size and position
continue to replace each other, it is considered one and the same
place.

This assimilation of a place or space with the body constituting it
gives rise to an interesting philosophical problem. Since a place is
identical with the body constituting it, how does a place retain its
identity and, therefore, remain the "same" place when it is replaced
by another body that now constitutes it? A return to the wine bottle
example will help to illustrate this point. Recall that first the
extension of the wine constituted the place inside the bottle and
then, after the wine was finished, that place inside the body was
constituted by the extension of the air now occupying it. So, since
the wine's extension is different from the air's extension, it seems
to follow that the place inside the wine bottle is not the exactly
same place but two different places at two different times. It is
difficult to see how Descartes would address this issue.

Another important consequence of Descartes' assimilation of bodies and
space is that a vacuum or an empty space is unintelligible. This is
because an empty space, according to Descartes, would just be a
non-extended space, which is impossible. A return to the wine bottle
will further illustrate this point. Notice that the place inside the
wine bottle was first constituted by the wine and then by air. These
are two different kinds of extended things, but they are extended
things nonetheless. Accordingly, the place inside the bottle is
constituted first by one body (the wine) and then by another (air).
But suppose that all extension is removed from the bottle so that
there is an "empty space." Now, distance is a mode requiring extension
to exist, for it makes no sense to speak of spatial distance without
space or extension. So, under these circumstances, no mode of distance
could exist inside the bottle. That is, no distance would exist
between the bottle's sides, and therefore the sides would touch.
Therefore, an empty space cannot exist between two or more bodies.

Descartes' close assimilation of body and space, his rejection of the
vacuum, and some textual issues have lead many to infer an asymmetry
in his metaphysics of thinking and extended things. This asymmetry is
found in the claim that particular minds are substances for Descartes
but not particular bodies. Rather, these considerations indicate to
some that only the whole, physical universe is a substance, while
particular bodies, for example, the wine bottle, are modes of that
substance. Though the textual issues are many, the main philosophical
problem stems from the rejection of the vacuum. The argument goes like
this: particular bodies are not really distinct substances, because
two or more particular bodies cannot be clearly and distinctly
understood with an empty space between them; that is, they are not
separable from each other, even by the power of God. Hence, particular
bodies are not substances, and therefore they must be modes. However,
this line of reasoning is a result of misunderstanding the criterion
for a real distinction. Instead of trying to understand two bodies
with an empty space between them, one body should be understood all by
itself so that God could have created a world with that body, for
example, the wine bottle, as its only existent. Hence, since it
requires only God's concurrence to exist, it is a substance that is
really distinct from all other thinking and extended substances.
Although difficulties also arise for this argument from Descartes'
account of bodily surfaces as a mode shared between bodies, these are
too complex to address here. But, suffice it to say that the textual
evidence is also in favor of the claim that Descartes, despite the
unforeseen problem about surfaces, maintained that particular bodies
are substances. The most telling piece of textual evidence is found in
a 1642 letter to Gibeuf:

From the simple fact that I consider two halves of a part of
matter, however small it may be, as two complete substances . . . I
conclude with certainty that they are really divisible. (AT III 477:
CSMK 202-203

These considerations in general, and this quotation in particular,
lead to another distinct feature of Cartesian body, namely that
extension is infinitely divisible. The point is that no matter how
small a piece of matter, it can always be divided in half, and then
each half can itself be divided in half, and so on to infinity. These
considerations about the vacuum and the infinite divisibility of
extension amount to a rejection of atomism. Atomism is a school of
thought going back to the ancients, which received a revival in the
17th century most notably in the philosophy and science of Pierre
Gassendi. On this account, all change in the universe could be
explained by the movements of very small, indivisible particles called
"atoms" in a void or empty space. But, if Descartes' arguments for
rejecting the vacuum and the infinite divisibility of matter are
sound, then atomism must be false, since the existence of indivisible
atoms and an empty space would both be unintelligible.
c. Physics

Descartes devised a non-atomistic, mechanistic physics in which all
physical phenomena were to be explain by the configuration and motion
of a body's miniscule parts. This mechanistic physics is also a point
of fundamental difference between the Cartesian and
Scholastic-Aristotelian schools of thought. For the latter (as
Descartes understood them), the regular behavior of inanimate bodies
was explained by certain ends towards which those bodies strive.
Descartes, on the other hand, thought human effort is better directed
toward the discovery of the mechanistic causes of things given the
uselessness of final causal explanations and how it is vain to seek
God's purposes. Furthermore, Descartes maintained that the geometric
method should also be applied to physics so that results are deduced
from the clear and distinct perceptions of the geometrical or
quantifiable properties found in bodies, that is, size, shape, motion,
determination (or direction), quantity, and so forth.

Perhaps the most concise summary of Descartes' general view of the
physical universe is found in part III, section 46 of the Principles:

From what has already been said we have established that all the
bodies in the universe are composed of one and the same matter, which
is divisible into indefinitely many parts, and is in fact divided into
a large number of parts which move in different directions and have a
sort of circular motion; moreover, the same quantity of motion is
always preserved in the universe. (AT VIIIA 100: CSM I 256)

Since the matter constituting the physical universe and its
divisibility were previously discussed, a brief explanation of the
circular motion of bodies and the preservation of motion is in order.
The first thesis is derived from God's immutability and implies that
no quantity of motion is ever added to or subtracted from the
universe, but rather quantities of motion are merely passed from one
body to another. God's immutability is also used to support the first
law of motion, which is that "each and everything, in so far as it
can, always continues in the same state; and thus what is once in
motion always continues in motion" (AT VIIIA 62-63: CSM I 241). This
principle indicates that something will remain in a given state as
long as it is not being affected by some external cause. So a body
moving at a certain speed will continue to move at that speed
indefinitely unless something comes along to change it. The second
thesis about the circular motion of bodies is discussed at Principles,
part II, section 33. This claim is based on the earlier thesis that
the physical universe is a plenum of contiguous bodies. On this
account, one moving body must collide with and replace another body,
which, in turn, is set in motion and collides with another body,
replacing it and so on. But, at the end of this series of collisions
and replacements, the last body moved must then collide with and
replace the first body in the sequence. To illustrate: suppose that
body A collides with and replaces body B, B replaces C, C replaces D,
and then D replaces A. This is known as a Cartesian vortex.

Descartes' second law of motion is that "all motion is in itself
rectilinear; and hence any body moving in a circle always tends to
move away from the center of the circle which it describes" (AT VIIIA
63-64: CSM I 241-242). This is justified by God's immutability and
simplicity in that he will preserve a quantity of motion in the exact
form in which it is occurring until some created things comes along to
change it. The principle expressed here is that any body considered
all by itself tends to move in a straight line unless it collides with
another body, which deflects it. Notice that this is a thesis about
any body left all by itself, and so only lone bodies will continue to
move in a straight line. However, since the physical world is a
plenum, bodies are not all by themselves but constantly colliding with
one another, which gives rise to Cartesian vortices as explained
above.

The third general law of motion, in turn, governs the collision and
deflection of bodies in motion. This third law is that "if a body
collides with another body that is stronger than itself, it loses none
of its motion; but if it collides with a weaker body, it loses a
quantity of motion" (AT VIIIA 65: CSM I 242). This law expresses the
principle that if a body's movement in a straight line is less
resistant than a stronger body with which it collides, then it won't
lose any of its motion but its direction will be changed. But if the
body collides with a weaker body, then the first body loses a quantity
of motion equal to that given in the second. Notice that all three of
these principles doe not employ the goals or purposes (that is, final
causes) utilized in Scholastic-Aristotelian physics as Descartes
understood it but only the most general laws of the mechanisms of
bodies by means of their contact and motion.
d. Animal and Human Bodies

In part five of the Discourse on Method, Descartes examines the nature
of animals and how they are to be distinguished from human beings.
Here Descartes argues that if a machine were made with the outward
appearance of some animal lacking reason, like a monkey, it would be
indistinguishable from a real specimen of that animal found in nature.
But if such a machine of a human being were made, it would be readily
distinguishable from a real human being due to its inability to use
language. Descartes' point is that the use of language is a sign of
rationality and only things endowed with minds or souls are rational.
Hence, it follows that no animal has an immaterial mind or soul. For
Descartes this also means that animals do not, strictly speaking, have
sensations like hunger, thirst and pain. Rather, squeals of pain, for
instance, are mere mechanical reactions to external stimuli without
any sensation of pain. In other words, hitting a dog with a stick, for
example, is a kind of input and the squeal that follows would be
merely output, but the dog did not feel anything at all and could not
feel pain unless it was endowed with a mind. Humans, however, are
endowed with minds or rational souls, and therefore they can use
language and feel sensations like hunger, thirst, and pain. Indeed,
this Cartesian "fact" is at the heart of Descartes' argument for the
union of the mind with the body summarized near the end of part five
of the Discourseand laid out in full in the Sixth Meditation.

Yet Descartes still admits that both animal and human bodies can be
best understood to be "machine[s] made of earth, which God forms." (AT
XI 120: CSM I 99). The point is that just as the workings of a clock
can be best understood by means of the configuration and motion of its
parts so also with animal and human bodies. Indeed, the heart of an
animal and that of a human being are so much alike that he advises the
reader unversed in anatomy "to have the heart of some large animal
with lungs dissected before him (for such a heart is in all respects
sufficiently like that of a man), and be shown the two chambers or
cavities which are present in it" (AT VI 47: CSM I 134). He then goes
on to describe in some detail the motion of the blood through the
heart in order to explain that when the heart hardens it is not
contracting but really swelling in such a way as to allow more blood
into a given cavity. Although this account goes contrary to the (more
correct) observation made by William Harvey, an Englishman who
published a book on the circulation of the blood in 1628, Descartes
argues that his explanation has the force of geometrical
demonstration. Accordingly, the physiology and biology of human
bodies, considered without regard for those functions requiring the
soul to operate, should be conducted in the same way as the physiology
and biology of animal bodies, namely via the application of the
geometrical method to the configuration and motion of parts.
9. Sensations and Passions

In his last published work, Passions of the Soul, Descartes provides
accounts of how various motions in the body cause sensations and
passions to arise in the soul. He begins by making several
observations about the mind-body relation. The whole mind is in the
whole body and the whole in each of its parts but yet its primary seat
is in a little gland at the center of the brain now known as the
"pineal gland." Descartes is not explicit about what he means by "the
whole mind in the whole body and the whole in each of its parts." But
this was not an uncommon way of characterizing how the soul is united
to the body at Descartes' time. The main point was that the soul makes
a human body truly human; that is, makes it a living human body and
not merely a corpse. Given Descartes' unexplained use of this phrase,
it is reasonable to suppose that he used it in the way his
contemporaries would have understood it. So the mind is united to the
whole body and the whole in each of its parts insofar as it is a soul
or principle of life. Accordingly, the body's union with the soul
makes it a living human body or a human body, strictly speaking (see
letter to Mersenne dated 9 February 1645). But, the "primary seat",
that is, the place where the soul performs its primary functions, is
the point where the mind is, in some sense, affected by the body,
namely the pineal gland.

Descartes maintains further that all sensations depend on the nerves,
which extend from the brain to the body's extremities in the form of
tiny fibers encased by tube-like membranes. These fibers float in a
very fine matter known as the "animal spirits." This allows these
fibers to float freely so that anything causing the slightest motion
anywhere in the body will cause movement in that part of the brain
where the fiber is attached. The variety of different movements of the
animals spirits cause a variety of different sensations not in the
part of the body originally affected but only in the brain and
ultimately in the pineal gland. So, strictly speaking, pain does not
occur in the foot when a toe is stubbed but only in the brain. This,
in turn, may cause the widening or narrowing of pores in the brain so
as to direct the animals spirits to various muscles and make them
move. For example, the sensation of heat is produced by the
imperceptible particles in the pot of boiling water, which caused the
movement of the animal spirits in the nerves terminating at the end of
the hand. These animal spirits then move the fibers extending to the
brain through the tube of nerves causing the sensation of pain. This
then causes various pores to widen or narrow in the brain so as to
direct the animals spirits to the muscles of the arm and cause it to
quickly move the hand away from the heat in order to remove it from
harm. This is the model for how all sensations occur.

These sensations may also cause certain emotions or passions in the
mind. However, different sensations do not give rise to different
passions because of the difference in objects but only in regards to
the various ways these things are beneficial, harmful or important for
us. Accordingly, the function of the passions is to dispose the soul
to want things that are useful and to persist in this desire Moreover,
the same animal spirits causing these passions also dispose the body
to move in order to attain them. For example, the sight of an ice
cream parlor, caused by the movement of the animal spirits in the eye
and through the nerves to the brain and pineal gland, might also cause
the passion of desire to arise. These same animal spirits would then
dispose the body to move (for example, toward the ice cream parlor) in
order to attain the goal of eating ice cream thereby satisfying this
desire. Descartes goes on to argue that there are only six primitive
passions, namely wonder, love, hatred, desire, joy and sadness. All
other passions are either composed of some combination of these
primitives or are species of one of these six genera. Much of the rest
of parts 2 and 3 of the Passions of the Soul is devoted to detailed
explications of these six primitive passions and their respective
species.
10. Morality
a. The Provisional Moral Code

In Part 3 of the Discourse on Method, Descartes lays out a provisional
moral code by which he plans to live while engaged in his
methodological doubt in search of absolute certainty. This code of
"three or four" rules or maxims is established so that he is not
frozen by uncertainty in the practical affairs of life. These maxims
can be paraphrased as follows:

1. To obey the laws and customs of my country, holding constantly
to the Catholic religion, and governing myself in all other matters
according to the most moderate opinions accepted in practice by the
most sensible people.
2. To be as firm and decisive in action as possible and to follow
even the most doubtful opinions once they have been adopted.
3. Try to master myself rather than fortune, and change my desires
rather than the order of the world.
4. Review the various professions and chose the best (AT VI 23-28:
CSM I 122-125).

The main thrust of the first maxim is to live a moderate and sensible
life while his previously held beliefs have been discarded due to
their uncertainty. Accordingly, it makes sense to defer judgment about
such matters until certainty is found. Presumably Descartes defers to
the laws and customs of the country in which he lives because of the
improbability of them leading him onto the wrong path while his own
moral beliefs have been suspended. Also, the actions of sensible
people, who avoid the extremes and take the middle road, can provide a
temporary guide to action until his moral beliefs have been
established with absolute certainty. Moreover, although Descartes does
seems to bring his religious beliefs into doubt in the Meditations, he
does not do so in the Discourse. Since religious beliefs can be
accepted on faith without absolutely certain rational justification,
they are not subject to methodological doubt as employed in the
Discourse. Accordingly, his religious beliefs can also serve as guides
for moral conduct during this period of doubt. Therefore, the first
maxim is intended to provide Descartes with guides or touchstones that
will most likely lead to the performance of morally good actions.

The second maxim expresses a firmness of action so as to avoid the
inaction produced by hesitation and uncertainty. Descartes uses the
example of a traveler lost in a forest. This traveler should not
wander about or even stand still for then he will never find his way.
Instead, he should keep walking in a straight line and should never
change his direction for slight reasons. Hence, although the traveler
may not end up where he wants, at least he will be better off than in
the middle of a forest. Similarly, since practical action must usually
be performed without delay, there usually is not time to discover the
truest or most certain course of action, but one must follow the most
probable route. Moreover, even if no route seems most probable, some
route must be chosen and resolutely acted upon and treated as the most
true and certain. By following this maxim, Descartes hopes to avoid
the regrets experienced by those who set out on a supposedly good
course that they later judge to be bad.

The third maxim enjoins Descartes to master himself and not fortune.
This is based on the realization that all that is in his control are
his own thoughts and nothing else. Hence, most things are out of his
control. This has several implications. First, if he has done his best
but fails to achieve something, then it follows that it was not within
his power to achieve it. This is because his own best efforts were not
sufficient to achieve that end, and so whatever effort would be
sufficient is beyond his abilities. The second implication is that he
should desire only those things that are within his power to obtain,
and so he should control his desires rather than try to master things
beyond his control. In this way, Descartes hopes to avoid the regret
experienced by those who have desires that cannot be satisfied,
because this satisfaction lies beyond their grasp so that one should
not desire health when ill nor freedom when imprisoned.

It is difficult to see why the fourth maxim is included. Indeed,
Descartes himself seems hesitant about including it when he states at
the outset that his provisional moral code consists of "three or four
maxims." Although he does not examine other occupations, Descartes is
content with his current work because of the pleasure he receives from
discovering new and not widely known truths. This seems to imply the
correct choice of occupation can ensure a degree of contentedness that
could not be otherwise achieved if one is engaged in an occupation for
which one is not suited. Descartes also claims that his current
occupation is the basis of the other three maxims, because it is his
current plan to continue his instruction that gave rise to them. He
concludes with a brief discussion of how his occupational path leads
to the acquisition of knowledge, which, in turn, will lead to all the
true goods within his grasp. His final point is that learning how best
to judge what is good and bad makes it possible to act well and
achieve all attainable virtues and goods. Happiness is assured when
this point is reached with certainty.
b. Generosity

After the Discourse of 1637, Descartes did not take up the issue of
morality in any significant way again until his correspondence with
Princess Elizabeth in 1643, which culminated in his remarks about
generosity in part 3 of the Passions of the Soul. Given the temporal
distance between his main reflections on morality, it is easy to
attribute to Descartes two moral systems – the provisional moral code
and the ethics of generosity. But Descartes' later moral thinking
retains versions of the second and third maxim without much mention of
the first and fourth. This indicates that Descartes' later moral
theory is really an extension of his earlier thought with the second
and third maxims at its core. At Passions, part 3, section 153,
Descartes claims that the virtue of generosity "causes a person's
self-esteem to be as great as it may legitimately be" and has two
components. First is knowing that only the freedom to dispose
volitions is in anyone's power. Accordingly, people should only be
praised or blamed for using one's freedom either well or poorly. The
second component is the feeling of a "firm and constant resolution" to
use one's freedom well such that one can never lack the will to carry
out whatever has been judged to be best.

Notice that both components of generosity relate to the second and
third maxim of the earlier provisional moral code. The first component
is reminiscent of the third maxim in its acknowledgment of people's
freedom of choice and the control they have over the disposition of
their will or desire, and therefore they should be praised and blamed
only for those things that are within their grasp. The second
component relates to the second maxim in that both pertain to firm and
resolute action. Generosity requires a resolute conviction to use free
will correctly, while the second maxim is a resolution to stick to the
judgment most likely to lead to a good action absent a significant
reason for changing course. However, a difference between these two
moral codes is that the provisional moral code of the Discourse
focuses on the correct use and resolute enactment of probable
judgments, while the later ethics of generosity emphasizes a firm
resolution to use free will correctly. Hence, in both moral systems,
the correct use of mental faculties, namely judgment and free will,
and the resolute pursuit of what is judged to be good is to be
enacted. This, in turn, should lead us to a true state of generosity
so as to legitimately esteem ourselves as having correctly used those
faculties through which humans are most in the likeness of God.
11. References and Further Reading
a. Primary Sources

* Descartes, René, Oeuvres de Descartes, eds. Charles Adam and
Paul Tannery, Paris: Vrin, originally published 1987-1913.
o This is still the standard edition of all of Descartes'
works and correspondence in their original languages. Cited in the
text as AT volume, page.
* Descartes, René, The Philosophical Writings of Descartes, trans.
John Cottingham, Robert Stoothoff, Dugald Murdoch and Anthony Kenny,
Cambridge: Cambridge Universiety Press, 3 vols.1984-1991.
o This is the standard English translation of Descartes
philosophical works and correspondence. Cited in the text as CSM or
CSMK volume, page.

b. Secondary Sources

* Ariew, Roger, Marjorie GRené, eds., Descartes and His
Contemporaries: Meditations, Objections, and Replies, Chicago:
University of Chicago Press, 1995.
o This is a collection of essays by prominent scholars about
various issues raised in the Meditations, objections to them and the
adequacy or inadequacy of Descartes' replies.
* Broughton, Janet, Descartes's Method of Doubt, Princeton:
Princeton University Press, 2003.
o A study of Descartes' method and its results.
* Dicker, Georges, Descartes: An Analytical and Historical
Introduction, Oxford: Oxford University Press, 1993.
o A clear and concise introduction to Descartes' philosophy.
* Frankfurt, Harry, Demons, Dreamers and Madmen: the Defense of
Reason in Descartes' Meditations, Indianapolis: Bobbs-Merrill, 1970.
o A classic examination of Descartes' Meditations.
* Garber, Daniel, Descartes' Metaphysical Physics, Chicago and
London: University of Chicago Press, 1992.
o Provides a detailed account of Cartesian science and its
metaphysical foundations.
* Gaukroger, Stephen, Descartes: An Intellectual Biography,
Oxford: Clarendon Press, 1995.
o Though somewhat technical, this is a very good biography
of Descartes' intellectual development emphasizing his early years and
his interests in mathematics and science.
* Kenny, Anthony, Descartes: A Study of His Philosophy, New York:
Random House, 1968.
o A classic study of Descartes' philosophy through the Meditations.
* Marshall, John, Descartes's Moral Theory, Ithaca and London:
Cornell University Press, 1998.
o One of the few book length explications of Descartes' moral theory.
* Rodis-Lewis, Genevieve, Descartes: His Life and Thought, trans.
Jane Marie Todd, Ithaca and London: Cornell University Press, 1998
o This is a very readable and enjoyable biography.
* Rozemond, Marleen, Descartes's Dualism, Cambridge: Harvard
University Press, 1998.
o Provides an interpretation of the real distinction between
mind and body, their causal interaction and theory of sensation within
the context of late Scholastic theories of soul-body union and
sensation.
* Secada, Jorge, Cartesian Metaphysics: The Late Scholastic
Origins of Modern Philosophy, Cambridge: Cambridge University Press,
2000.
o An at times technical, though readable, account of the
whole of Descartes' metaphysics from within the context of late
Scholasticism.
* Skirry, Justin, Descartes and the Metaphysics of Human Nature,
London: Thoemmes-Continuum Press, 2005.
o Provides an account of Descartes' theory of mind-body
union and how it helps him to avoid the mind-body problem.
* Verbeek, Theo, Descartes and the Dutch: Early Reactions to
Cartesian Philosophy 1637-1650,Carbondale: Southern Illinois
University Press, 1994.
o Provides a history and account of the controversies at
Utrecht and Leiden.
* Williston, Byron and Andre Gomby, eds., Passion and Virtue in
Descartes, New York: Humanity Books, 2003.
o An anthology of essays by many noted scholars on
Descartes' theory of the passions and aspects of his later moral
theory.
* Williams, Bernard, Descartes: The Project of Pure Enquiry,
Sussex: Harvester Press, 1978.
o Classic account of Descartes' philosophy in general.
* Wilson, Margaret, Descartes, London and Boston: Routledge and
Kegan Paul, 1978.
o A classic in Descartes scholarship covering the whole of
his philosophy as expressed in the Meditations.