them out as intrinsically different from states of consciousness such
as thinking. A plausible view is that the difference should be
accounted for by the fact that, in having an experience, the subject
is somehow immediately aware of a range of phenomenal qualities. For
example, in seeing, grasping and tasting an apple, the subject may be
aware of a red and green spherical shape, a certain feeling of
smoothness to touch, and a sweet sensation. Such phenomenal qualities
are also immediately present in hallucinations. According to the
sense-data theory, phenomenal qualities belong to items called
"sense-data." In having a perceptual experience the subject is
directly aware of, or acquainted with, a sense-datum, even if the
experience is illusory or hallucinatory. The sense-datum is an object
immediately present in experience. It has the qualities it appears to
have.
A controversial issue is whether sense-data have real, concrete
existence. Depending upon the version of the sense-data theory
adopted, sense-data may or may not be identical with aspects of
external physical objects; they may or may not be entities that exist
privately in the subject's mind. Usually, however, sense-data are
interpreted to be distinct from the external physical objects we
perceive. The leading view, in so far as the notion is appealed to in
current philosophy, is that an awareness of (or acquaintance with)
sense-data somehow mediates the subject's perception of
mind-independent physical objects. The sense-datum is the bearer of
the phenomenal qualities that the subject is immediately aware of.
Knowledge of sense-data has often been taken to be the foundation upon
which all other knowledge of the world is based. For a variety of
different reasons that will be explored below, the notion of
sense-data is now widely held to give rise to a number of difficult,
if not insurmountable, problems.
1. Motivations for Introducing Sense-Data
Sense-data were originally introduced in order to account for a number
of puzzling perceptual phenomena. Before we reflect upon the matter,
we are inclined to take perception to be direct and straightforward.
If I see an apple in front of me in broad daylight, the natural
assumption is that the very apple I see is immediately present in my
experience. In normal circumstances an object appears as it really is.
I believe that the properties I am aware of in my experience, such as
the roughly spherical shape, and red and green color, belong to the
apple in front of me. There are, however, two main lines of argument
that suggest matters are not quite as straightforward as common sense
assumes:
The first general type of argument emphasizes epistemological
considerations, and focuses on questions about whether our
perceptually based claims about the world can be properly justified,
and whether, through experience, we can arrive at any knowledge of the
world that is beyond doubt. If our goal is to arrive at certain
knowledge about the nature of the real world, then one suggestion, in
line with empiricist views, is that we should begin with what is
immediately given in experience. There are, however, difficulties
attaching to the view that our perceptual experiences provide us with
knowledge of a mind-independent physical world. It is suggested by
advocates of sense-data (and others) that claims about the world that
are based upon experience cannot be certain. The reason is that
experience is not always a reliable guide to how things really are.
Various perceptual phenomena raise prima facie puzzles about how our
experiences can give us genuine knowledge of a mind-independent
reality.
In perceptual illusions, by definition, some physical object is
perceived, but the way an object appears to the perceiving subject is
not how it really is. Thus in certain lighting conditions a red object
can appear green; a straight stick, half immersed in water, will
appear crooked; the whistle of an approaching train sounds a higher
pitch than it really is. In hallucinations, there is no object at all
present that is relevant to how things appear to a subject: someone
who has taken drugs may seem to see a strange animal, when there are
no animals present in the vicinity. In double vision, an object
appears to be situated in more than one location relative to the
subject. In most of these cases we are not usually deceived as to how
things really are. However, the fact remains that in such cases things
appear differently from the way they really are. These two puzzle
cases—illusions and hallucinations–were often assumed to raise
epistemological issues, about how we come to have knowledge about the
world, and about whether we are justified in the perceptual judgments
we make about the physical objects in our surroundings.
One motive, therefore, for introducing the notion of sense-data,
involves the epistemic claim that there is a certainty attaching to
propositions about experience, which propositions about the physical
world are thought to lack. Under the influence of "the argument from
illusion" (discussed further below in section 3), some writers argued
that the phenomenal qualities that appear immediately to the subject
in experience belong to items that are distinct from physical objects.
These items are termed sense-data. Propositions about the sense-data
immediately present in experience are supposed to have a certainty
that other empirical propositions lack.
A second line of thought suggests that the fundamental problems
connected with perceptual experience are metaphysical, and concern the
proper analysis of what perceptual consciousness involves, and how our
perceptual experiences are related to the physical objects and events
that we perceive. Reflection upon common sense, and, in particular,
upon scientific extensions of common-sense knowledge, raises complex
issues concerning the relation between our experiences and the
objective world we perceive. When we reflect upon perceptual
experience from an external point of view, and think about what is
going on when another person is perceiving, then it is natural to
conceive of the process of perception as involving a series of
distinct, causally related events. In considering a subject of some
experiment on vision in a laboratory, we may be lead to distinguish
between the fact that an object X is situated in front of the subject,
and the inner experience E that the subject has, as a result of
looking in the direction of X. This external perspective on perceptual
experiences can suggest the thought that perception involves a number
of stages, linking what is situated outside the subject by a causal
chain of neurophysiological events to the culminating experience E,
which perhaps supervenes on the subject's brain state. We can combine
this thought with the idea that an experience of exactly the same type
could have been caused in an abnormal manner, without the object X
being present – the subject could have had a hallucinatory experience
of the same type, supervening upon the same kind of proximal brain
state, but triggered by a quite different distal cause, such as, for
example, the ingestion of a drug.
This way of considering perception, called by Valberg "The problematic
reasoning," suggests that what a person is immediately consciously
aware of in experiencing an object is something logically distinct
from that object (Valberg, 1992, ch. 1; see also Robinson, 1994, ch.
6; but compare Martin, 2004). This reasoning is not dependent upon any
particular detailed set of scientific theories about perception. It
arises at a very general level. But, as Locke appreciated (1690, Book
II, Chapter 8), taken in connection with more specific scientific
arguments about the intrinsic nature of objects, it can invite the
further thought that the properties which the sciences attribute to
physical things are very different in kind from the properties we are
aware of in experience. For, it might be argued, the properties that
science attributes to objects are either basically spatial in nature,
or involve special forces and fields (such as electromagnetic
phenomena) that we do not observe directly; hence they are distinct
from many of the phenomenal qualities that we are immediately aware
of. Finally, science tells us that there is a time-lag between the
moment of the event at the start of the perceptual chain, when
information about the state of a physical object is transmitted to the
subject, and the event comprised by the subject experiencing that
object. I can, in some sense, see a distant star, even though that
star may have ceased to exist before I was born. Thus a second motive
for introducing sense-data appeals to the alleged distinction between
experiences and the physical objects we perceive. Experiences, on this
view, are to be analyzed in terms of the immediate awareness of
sense-data.
Both the above lines of thought are supported by some of the
phenomenological considerations that relate to our first-person,
subjective point of view. The claim that all sense-data belong to the
same class of entities, and should collectively be distinguished from
physical objects, is based in part upon the supposed fact that
experiences of different kinds share a degree of intrinsic
resemblance. It is possible for cases of veridical perception,
perceptual illusion, and hallucination all to share a subjective
similarity. From the standpoint of the subject, such situations are,
at least on some occasions, phenomenologically indistinguishable from
each other. So, for example, if a person is aware of something red and
round, and it seems to them that they are seeing an apple, it is
possible that they are actually seeing an apple, or that they are
suffering from some illusion, either of a green apple, or of some
other object; or they may simply be hallucinating an apple. There may
therefore be no physical object situated in the subject's environment
possessing the properties that the subject seems to see. Nevertheless,
it seems that the properties of redness and roundness are in some way
immediately present to the subject's experience, in a manner different
from belief. On the sense-data view, the experienced properties of
visual redness and roundness are attributed to an existing item, a
sense-datum, of which the subject is immediately aware, irrespective
of whether there exists some matching physical object in the
surrounding environment. The postulation of sense-data as items in
common to the various kinds of experiences that we can have, whatever
their status, explains their subjective similarity.
Considerations such as these, although not always explicitly
formulated, nor always clearly distinguished, have prompted the
introduction of the notion of "sense-data." The general idea is that
we need first to get clear about precisely what is present in
immediate experience whenever we perceive a physical object. We should
analyze experience itself, before any assumptions about reality are
brought into play.
2. The Precise Characterization of Sense-Data
Sense-data can be characterized as the immediate objects of the acts
of sensory awareness that occur both in normal perception, and also in
related phenomena such as illusion and hallucination. The central idea
is that whenever I have an experience in which I perceive, or seem to
perceive, a physical object, there is something immediately present to
my consciousness. This "something" is a distinct object, a sense-datum
that I am aware of, which actually has the qualities it appears to
have. There is a mental act of awareness that involves a relation to a
distinct object (Moore, 1903 and 1913). This act of awareness is
sometimes also called an act of "acquaintance" or an act of
"apprehension". Sense-data entities, although often interpreted as
non-physical, have real concrete existence; they are not like
imaginary objects, such as unicorns, nor like abstract objects, such
as propositions.
Suppose, for example, I see, in the ordinary sense of the term, a red
apple in normal daylight. Traditionally it has been held that there is
a small range of sensible qualities belonging to physical objects that
I am aware of immediately, without drawing any inferences (Berkeley,
1713, First Dialogue). Thus, for example, it is held that in seeing
the apple, I am immediately aware of its color and shape; in hearing a
bell, I am immediately aware of a certain volume, pitch and timbre (or
tonal quality) which lead me to believe that I am hearing a bell.
Other such sensible qualities include tastes, odors and tangible
qualities.
According to the sense-data view, these sensible qualities are in fact
phenomenal qualities that belong to the sense-data somehow immediately
present to conscious experience. Thus in seeing the apple, I am in
fact immediately aware of a visual sense-datum of a certain roughly
round shape and red color, which may or may not be identical with some
entity in the surrounding world. If I hallucinate a ringing noise in
my ear, there exists some sense-datum, a sound that I am immediately
aware of. Sense-data can be characterized by a set of determinate
qualities belonging to different quality spaces. Visual sense-data
thus have color, and also spatial properties, of shape, position, and
perhaps also of depth. Auditory sense-data have pitch, volume and
timbre, and so on.
There has never been a single universally accepted account of what
sense-data are supposed to be; rather, there are a number of closely
related views, unified by a core conception. This core conception of a
sense-datum is the idea of an object having real existence, which is
related to the subject's consciousness. By virtue of this relation the
subject becomes aware that certain qualities are immediately present.
This means that sense-data have the following basic characteristics:
(a) Sense-data have real existence – they are not like the
intentional objects of thoughts and other propositional attitudes;
that is, they are concrete (as opposed to abstract) items, and the
manner of their existence takes a different form from the existence of
the content of a person's thought;
(b) The subject's act of awareness involves a unique and primitive
kind of relation to the sense-datum: this relation is not one that can
be further analyzed;
(c) The sense-datum is an object that is distinct from the act of
awareness of it;
(d) Sense-data have the properties that they appear to have;
(e) The act of awareness of a sense-datum is a kind of knowing,
although it does not involve knowledge of a propositional kind;
In addition, sense-data have often been claimed to have the following
characteristics:
(f) Sense-data have determinate properties; for example, if a
sense-datum is red, it will have a particular shade of red;
(g) Sense-data are (usually) understood as private to each subject;
(h) Sense-data are (usually) understood to be distinct from the
physical objects we perceive.
Of these, perhaps the most important – and problematic – claim is (e),
the idea that being aware of a sense-datum involves some kind of
knowledge of facts about the sense-datum (see Sellars, 1956, Part I).
Sense-data were originally introduced as the "direct objects" of such
acts of awareness as occur in perception and related experiences. Talk
of "objects," it should be noted, is ambiguous. In the sense intended,
sense-data are entities that have real existence, of a non-abstract
form. This means that sense-data are not like the objects of mental
attitudes such as desire, belief, and fear. Such mental attitudes or
states are said to have intentional objects, and in so far as the
state is concerned, need not be about objects that actually exist. If
I am hungry, and desire an apple, and believe incorrectly that there
is an apple in the fridge, then although no physical apple exists in
the relevant sense, my states are described in terms of what they
represent, or are about. The apple, which I falsely believe to exist,
in fact lacks real existence, and has only what is called "intentional
in-existence," by virtue of my representing it in my mistaken belief
(see Brentano, 1874). But if I see or hallucinate an apple, then
according to the sense-data view there is an actual red object of some
kind – a sense-datum – that has real existence.
The acts by which the subject is related to sense-data are therefore
not representational in the way that thoughts are. They do not have a
structure analogous to that of purely intentional states such as
desire and belief. So the sense-data theory holds that when the
subject has a visual (auditory, and so forth) sensation, there is some
real two-term relation of awareness or acquaintance that connects the
presented sense-datum to the subject's mind. The sense-datum is not an
abstract object in the way that a proposition is. Nevertheless, this
act of awareness is supposed to be, at the same time, a form of direct
knowledge of the sense-datum object. It involves some kind of
understanding on the subject's part. Knowledge of the sense-datum is
not inferred from any prior conscious state.
Although acts of awareness are mental events in the subject's mind,
the actual sense-datum itself is not a mental item in the way that a
pain might be held to be something mental. According to the original
formulations of the view, a sense-datum is distinct from the subject's
act of mind, and the subject only becomes aware of it by entering into
the unique relation of awareness to it. The sense-datum is therefore
not necessarily connected to the subject's mind: in theory, the
sense-datum could exist independently of the subject being aware of it
(see below in section 3). Nevertheless, since the awareness of a
sense-datum is supposed to be in some sense "immediate," statements
about sense-data have been variously claimed to be indubitable,
infallible and incorrigible; there is, however, no settled view as to
the status of such claims.
The classical conception of sense-data fits naturally with
foundationalist theories of knowledge. Firstly, sense-data can play a
role as the entities a subject has some kind of awareness of before
arriving at beliefs about anything else: knowledge of sense-data is
supposedly antecedent to knowledge of the physical world, and
constitutes the justification for beliefs about the existence of
physical things. Secondly, sense-data can, on this view, play a role
in the empiricist explanation of how, in general, words acquire the
meanings they have – the idea being that either words stand directly
for properties of sense-data, or can be defined by reference to such
words.
3. The Origins and Early Developments of the Idea of Sense-Data
The expression "data of the senses" and its cognates gained currency
towards the end of the nineteenth century, particularly in the work of
William James (see, for example, James, 1897). The concept of
sense-data was refined in the work of Bertrand Russell, and G. E.
Moore, prominent amongst the philosophers of this period who appealed
to the idea. The view harkens back to the theory of sensory ideas or
impressions put forward in the work of empiricist philosophers such as
Locke, Berkeley, and Hume. However, Moore's seminal paper, "The
Refutation of Idealism" (1903), which introduced the act-object model
of sensing, may be seen as the origin of the essential features of the
modern sense-data view. The notion was extensively appealed to in
metaphysical and epistemological discussions throughout the first half
of the twentieth century, for example in the work of Russell (1912 and
1918), Broad (1925), and Price (1932), and particularly in the works
of Ayer (1940, 1956) and other positivistically inclined philosophers.
Since a sense-datum is logically independent of the act of awareness
whereby the subject is conscious of it, it follows that sense-data
can, in theory, exist outside of consciousness, without any subject
being acquainted with them. The general class to which sense-data
belong are known as Sensibilia or Sensibles. A sensible becomes a
sense-datum by entering into a relation of awareness (or acquaintance)
with the mind of a subject. This initial characterization leaves open
the precise relation that holds between sense-data and physical
objects. The category of sense-data, according to the original
formulations of writers such as Russell, Moore and Price, is therefore
introduced in an ontologically neutral way (see in particular Moore,
1913; Price, 1932; see also Bermudez, 2000; though compare Broad,
1925).
The answer to the question, "Do sense-data exist?" is therefore
complex. Strictly speaking, the answer comprises two stages. In formal
terms, if the act-object analysis of experience is correct, it follows
from the fact that experiences occur that there are such things as
sense-data. Sense-data are the objects, whatever their nature, that
are immediately present in experience. Thus, originally, the term
sense-data was introduced as a quasi-technical term to help clarify
exactly what experience involves, so as to enable us to explore the
various puzzling phenomena mentioned above. According to this original
conception of sense-data, it is therefore an open question whether
sense-data can be identified with physical objects, or their parts
(for example, for visual sense-data, the facing surfaces). More
usually, however, the question "Do sense-data exist?" is interpreted
to mean, "In normal perception, are we aware of sense-data entities
that are distinct from mind-independent physical objects?" Given the
facts of illusion, and other kinds of perceptual error, it was held by
most theorists that sense-data could not be directly identified with
ordinary physical objects, conceived of according to common sense;
nor, for the same reason, could they be identified with parts of
ordinary objects (such as facing surfaces, and so forth).
For many early advocates of the concept, including both Moore and
Russell, sense-data were indeed understood to be distinct from
physical objects. This treatment of sense-data was bound up with an
acceptance of the argument from illusion.
The argument from illusion can be briefly summarized as follows:
supposedly, what I am aware of immediately is just how things appear
to me. When I see a red physical object that seems green (perhaps
because of unusual lighting conditions), some entity exists in the
situation that actually is green; it is this green item that is
immediately present to my consciousness. Because of the difference in
their properties, it would seem to follow that we cannot identify the
presented green entity with the red physical object. So what I am
immediately aware of is some different entity, a sense-datum, and not
a physical object. The existence of such sense-data entities can then
be appealed to in order to account for the similarity between
veridical and hallucinatory experiences.
A number of replies have been developed to the argument from illusion,
and it was debated at great length during the twentieth century (and
indeed the argument itself goes back at least as far as Berkeley). A
proper appraisal is outside the scope of the present discussion (see
in particular Ayer, 1940 and 1967; Austin, 1962; and, for a recent
clear and detailed discussion, Smith, 2002). More recently, as noted
in Section 1 above, some writers have concentrated upon the causal
argument for the introduction of sense-data: this argument suggests
that since hallucinatory experiences are in principle subjectively
indistinguishable from veridical experiences, all experiences must
involve an immediate awareness of entities that belong to the same
common kind. There must be a "highest common factor" shared by all
experiences. Since I could have a given type of experience – say, of
seeming to see a red ball – while hallucinating when no such physical
object is present in my surroundings, the common factor cannot include
an external physical object. The common factor is therefore
interpreted as an experience involving an awareness of sense-data, a
special class of entities that are distinct from all external physical
objects. For such reasons it can be suggested that in some way the
awareness of sense-data is either equivalent to, or supervenes upon,
the subject's brain states alone. Even in veridical perception the
subject immediately experiences sense-data that are distinct from the
distal object perceived (Grice, 1961; Valberg, 1992; and Robinson,
1994).
If sense-data form a homogenous class of entities, and it is held that
they can never be identified with the ordinary physical objects
outside the subject's body, then the question arises as to how in fact
sense-data are related to the physical objects that we assume make up
the external world. According to the Causal Theory of Perception
(sometimes called the "Representative Theory," or "Indirect Realism")
sense-data are caused by the physical objects that in some sense we
perceive, perhaps indirectly, in our local surroundings. When I see an
apple, that apple causes me to be immediately aware of a sense-datum
of a red and green round shape, a sense-datum that roughly
"corresponds" to the facing surface of the real physical apple. Some
writers have objected to the Causal Theory on epistemic grounds. It
has sometimes been claimed that physical objects are made unknowable
on the causal account, or that demonstrative reference to physical
objects would not be possible if the theory was correct (for
discussion see Price, 1932; Armstrong, 1961; and Bermudez, 2000; but
for replies to this criticism compare Grice, 1961, and Jackson, 1977).
Another possibility, explored particularly by Russell, was the
metaphysical thesis that sense-data might be equated with the ultimate
constituents of the world. If sense-data can be understood in this
way, then both ordinary common-sense objects, and hallucinatory
images, might be constructed from them; and possibly even the self
might be a logical construction out of such entities. Under the
influence of the theory developed by William James known as "Neutral
Monism," Russell analyzes a physical object such as a chair as a
series of classes of sense-data; the self is also analyzed in a
parallel way, as a distinct series of classes of sense-data, some of
which include the sense-data that make up the chair (Russell, 1918,
Lecture viii). (What this view means, very roughly, is that sense-data
are taken to be the basic constituents of the world. Statements about
selves, and about physical objects, are supposed to be definable in
terms of statements about sense-data, in much the same way that it
might be held that statements about nations might be defined in terms
of statements about lands and inhabitants.)
Other writers put forward the related theory of phenomenalism, a view
which was first developed in detail by John Stuart Mill, although it
was in fact briefly canvassed by Berkeley (1710, sec 3). According to
phenomenalism, physical objects are thought of as constructions out of
actual and possible sense-data. That is, a statement asserting the
existence of a given particular physical object, such as an apple in
front of me, is supposed to be analyzable in terms of statements about
the sense-data experiences I am currently having of the apple, or that
I would have if I were to reach out and pick it up. To say that there
is an apple unperceived in the fridge is to say something like: "If I
were to open the door of the fridge and if my eyes were open, etc, I
would have sense-data of a reddish, apple-like shape, and so forth."
The idea is that any statement that on the surface appears to be about
a physical object can, by analogous methods, be translated into a set
of statements which refer only to actual and possible sense-data, and
do not refer to physical objects. But how to fill out the
phenomenalist analysis in a more detail, so as to avoid any
circularity (and to remove any appeal to the "et ceteras") becomes
problematic: in the example briefly sketched above, the analysis of
the unperceived apple makes reference to the fridge door, and also to
my own bodily states, and hence is incomplete (for a discussion see
Chisholm, 1957; Urmson, 1956).
A different, though related approach to the question, put forward in
various forms by Ayer, held that there was no genuine problem about
the ontological status of sense-data and their relation to physical
objects. We should instead regard the issue as a question of finding
the most useful convention for discussing the various facts relating
to perceptual phenomena. According to this view, acceptance of the
sense-data theory amounts to a decision to employ a certain
terminology, without deep consequences for metaphysics and
epistemology. Provided suitable adjustments were made elsewhere in
one's system, any theory of perception could be adopted. Alternative
theories "are, in fact what we should call alternative languages"
(Ayer, 1940; similar ideas were mooted by Paul, 1936). Ayer's own
preferred language was in fact very close to the phenomenalist
analysis sketched above.
The idea of sense-data came under attack from three general
directions: (i) from phenomenologically based criticisms, drawing upon
some of the findings of Gestalt psychology (for example,
Merleau-Ponty, 1945; Firth, 1949/50); (ii) from anti-foundationalist
views emanating from the philosophy of science, which denied a
clear-cut distinction between observation and theory (for example,
Hanson, 1958), and (iii) from the standpoint of ordinary language
philosophy and epistemology (for example, in the powerful critique
presented by Austin, 1962). As a result of these combined attacks, in
the second half of the twentieth century the notion fell into disuse,
despite some careful subsequent defences of the idea (see, for
example: Ayer, 1967; Sprigge, 1970; and Jackson, 1977). Nevertheless,
although explicit appeal to the notion has now largely been abandoned,
the core conception still exerts a powerful influence upon our ways of
thinking about perception in particular and epistemology in general.
4. The Objections to Sense-Data
Objections to the view that sense-data exist in a form that is
different from the existence of ordinary physical objects have been
advanced on a number grounds. These objections fall into three broad
categories.
a. Phenomenological Objections
There is a central phenomenological objection to the idea of
sense-data, which can be formulated in various ways. The basic
contention is that the postulation of sense-data entities runs counter
to ordinary perceptual experience. My immediate experience, when in
the normal case I look around me, consists in the awareness of
"full-bodied physical objects" (Merleau-Ponty, 1945; Firth, 1949; see
also the discussion in Austin, 1962). First-person perceptual
judgments are not mediated; I am not aware of making inferences from a
subjective awareness of sense-data to the objective judgments I form
about physical objects.
b. Coherence Objections
Perceptual experience is indeterminate. If I briefly see a speckled
hen, I see that it has some speckles, but I am not aware of it as
having a definite number of speckles. According to the sense-data
view, the sense-datum of the hen I am aware of necessarily has the
properties it appears to have. Hence the sense-datum of the hen has an
indeterminate number of speckles. Yet if what I am aware of when I see
the hen is a visual shape, an actual existing speckled sense-datum,
then surely it must have a determinate number of speckles; this seems
to lead to the contradiction in the properties that we attribute to
the sense-datum (Barnes, 1944; but compare Jackson, 1977).
There are no clear-cut identity conditions for sense-data, and hence
no principled grounds for answering such questions as, how many visual
sense-data are present in my visual field? How long do they last? To
this objection the sense-data theorist might well reply that in this
respect sense-data are not logically worse off than many other kinds
of entity; the identity conditions of ordinary physical objects are
similarly not clear-cut (Jackson, 1977).
A further problem consists in saying where sense-data exist. Are they
in some private space of which only the subject can be aware? Or do
they exist in physical space? If the former, we need to explain how
private subjective spaces are related to a common public space. If the
latter, then we need to provide some account of how the properties of
sense-data relate to those of the physical objects which are situated
at the same location (Barnes, 1944).
Upholding the sense-data theory has sometimes been held to entail an
acceptance of the idea of a "Private Language," a view that
Wittgenstein argued to be incoherent. Wittgenstein's views on this
question are not easy to interpret, and a full assessment of them is
outside of the scope of this article. He was prepared to accept the
existence of inner states and processes, provided they were connected
with outer criteria (Wittgenstein, 1953, remark 580, and footnote to
149). Other passages (such as 1953, remarks 398-411) suggest that the
real target of his criticism is the "act-object" model of experience.
If Wittgenstein's ideas are accepted, this would appear to show the
incoherence any foundationalist conception of sense-data, in which
knowledge of sense-data precedes, and serves as the basis for other
forms of knowledge (see also Sellars, 1956 and 1963).
Perhaps the most fundamental of the objections to the coherence of the
notion of sense-data concerns the unique "act-object" relation that is
supposed to link the sense-datum to the subject's consciousness.
Crucially, the nature of this relation is left unexplained. Attempts
to explain the relation, it is claimed, lead to a regress (Ryle, 1949,
ch. 7; Kirk, 1994). This objection is discussed more fully below, in
section 5c.
c. Epistemological Objections
There is a general worry, originating in the work of Descartes and
Locke, that the acceptance of entities equivalent to sense-data, when
these are interpreted as distinct from physical objects, leads to
problems in the theory of knowledge. If we are only aware of
sense-data, and not of the physical objects themselves, how can we be
sure that the properties of physical objects resemble those that
appear to us? How can we even be sure that physical objects do exist?
Isn't the sense-data theorist saddled with a serious and insoluble
sceptical problem about the external world? The acceptance of
sense-data, it is argued, leads inevitably to idealism or scepticism.
Such criticisms have been widely advanced, but it is not at all clear
how cogent they are. On any theory of perception problems about the
relation between appearance and reality can be raised; they do not
attach only to the sense-data view (for some discussion, see:
Armstrong, 1961; Jackson, 1977; Robinson, 1994; M. Williams, 1996).
5. The Deeper Issues Involved in the Idea of Sense-Data
a. The Underlying Tensions in the Idea
Advocates of sense-data have produced many responses to these specific
objections to sense-data. But no adequate assessment is possible
without a proper examination of the underlying features of the
original sense-datum theory, which give rise to the various
difficulties listed. All the objections above trace back to deeper
tensions arising from three central claims that form part of the
original conception of sense-data. These are first summarized, before
being subjected to a closer examination:
Claim 1: Sense-data form a homogenous class of entities, whose members
can in principle exist independently of acts of awareness:
Claim 2: The awareness of a sense-datum is a sui generis act of
awareness, involving a two-term real relation between an act of mind
and a particular existent:
Claim 3: The awareness of a sense-datum is a form of sensory
experience that somehow provides the subject directly with knowledge
of facts about the sense-datum:
These three features of the sense-datum theory will be examined in turn.
b. The Class of Sense-Data
Do all sense-data, defined merely as the objects of immediate
awareness in veridical, illusory and hallucinatory experiences, belong
to the same ontological category? This question leads to a number of
further questions: How are sense-data related to physical objects? Are
some of the sense-data that occur in ordinary veridical perception
identical with the ordinary physical objects we perceive, or are they
in all cases distinct from them? Can sense-data have properties of
which the subject is not aware?
Assuming that we can make sense of the idea of acts of awareness, and
that the formal notion of sense-data as the objects of such acts can
be given a clear meaning, the precise ontological status of sense-data
is a further issue, a matter of some debate. It should not be assumed
without further argument that they constitute a homogenous class, and
that, for example, the type of sense-datum present in a hallucination
is of the same type as that present in the veridical experience of an
external physical object. As we have noted, in the original
formulations of the concept, sense-data are initially introduced in a
neutral way – the idea being that their exact ontological status is a
matter to be investigated. As a consequence of the adoption of the
act-object conception of awareness, sense-data are held to be, in an
important way, distinct from the subject's mind. To the extent that a
sense-datum is present to experience, and the subject is aware of that
sense-datum as having a property F, it follows that the sense-datum
must have that property F; but arguably it is possible that the
sense-datum also has some other property G of which the subject is not
aware (Moore, 1918; Ayer 1945; and Jackson, 1977). It is therefore
possible that, in veridical perception, what the subject is
immediately aware of is a sense-datum that is in fact identical with a
physical object, whereas in hallucinations the sense-data present are
non-physical items (Bermudez, 2000).
c. Awareness as a Real Relation
How can the nature of the relation involved between the act of
awareness and the sense-datum be further characterized? How is the
intrinsic nature of the subject's experience (in so far as this
involves the very act itself) related to the properties possessed by
the existing sense-datum object? Should the sense-datum present in
experience be understood as a particular entity, distinct from the act
of awareness (or acquaintance), or should it be analyzed as an aspect
of the character of the act?
One of the most serious objections raised against the whole notion of
sense-data is that the nature of the relation between the subject's
conscious act of awareness and the sense-datum object is obscure, and
cannot be coherently explicated. If the relation is modeled upon
perceiving, then the view leads to an infinite regress. For suppose we
try to analyze the situation where S sees some physical object X by
the postulation of an additional entity, a sense-datum Y, such that in
seeing X, S is directly aware of the sense-datum Y; suppose further,
that the relation of direct awareness of a sense-datum is explained as
similar to the relation of seeing an object; then by a like argument,
in order to explain how S can be aware of the sense-datum Y, it seems
that we must postulate a third entity Z, in order to account for the
relation of S to Y, and so on ad infinitum. Of course, this regress
can be blocked by denying that "awareness" (or "acquaintance") is to
be understood by analogy to perceiving, but this then leaves the
nature of the awareness relation unexplained; all that can be said is
that the relation of awareness is unanalyzable (Ryle, 1949; Kirk,
1994).
The problem here is exacerbated by the fact that such acts of
awareness also have a peculiar metaphysical character that
distinguishes them in general from other kinds of acts. Although the
act is supposed to involve a two-term relation connecting two
particulars, it also functions as a unique kind of "bridge" or link
between consciousness and external items supposedly distinct from the
mind. But it is hard to make sense of the claim that act and object
are distinct entities. The act of awareness mysteriously "conveys" the
phenomenal qualities of the object over to the conscious mind of the
subject, making them present on the mental side of the relation, in
the subject's experience. It is not clear how any relation could play
this role.
Connected with these problems is the issue of the status in the
subject's consciousness of the alleged acts of awareness. Moore
himself drew attention to the fact that when I try to focus upon my
act of awareness, all that I am aware of is the object of that act; I
am not in any direct way conscious of the act itself. The act of
awareness is supposed to be "transparent" or "diaphanous": it is not
something that is present in consciousness, when the subject is aware
of its object. Introspection is of no help here, for even when I
introspect I cannot discern anything other than the object I am aware
of in having an act, the sense-datum. For example, when I see the oval
petal of a blue flower, I am, supposedly, directly aware of a blue,
oval shaped sense-datum. All that closer introspection of my
consciousness reveals is just the very same blue oval shape that was
there in the first place. So what grounds are there for saying that
acts take place, acts that are distinct from their objects?
The act-object conception of the awareness of sense-data is also
connected with a fundamental tension in the notion, concerning the
extent to which the subject becomes aware of all and only the
properties of the sense-datum. The tension is between the idea that
the sense-datum has just those properties of which the subject is
immediately aware of in being aware of the sense-datum, and the idea
that there are further properties that belong to the sense-datum
independently of whether the subject is aware of them. This tension
leads to contradictory claims about the status of sense-data. Thus
Russell held that sense-data are private to the subject (1914); more
consistently, Moore held that it was an open question whether
sense-data were private – this was not a feature of sense-data that
followed automatically from the definition of the notion (1918). One
attempt to avoid these various difficulties is the adverbial analysis
of experience, discussed below in section 6b.
d. Awareness as Both Sensing and Knowing
In what way does an act of awareness, whereby a sense-datum entity is
experienced, involve knowledge of the particular sense-datum that is
present? How is the phenomenal (or sensory) aspect of experience
related to the employment of concepts when the subject attends to the
sense-datum and is aware of it as belonging to a certain kind?
Arguably the most fundamental difficulty arising from the notion of
sense-data is the extent, and manner, in which concepts are involved
in the awareness of a sense-datum. As Sellars pointed out, in many
writings on sense-data there was an equivocation between treating the
awareness of sense-data as, (i) an extensional non-epistemic relation
between the mind and an independent existing entity, or alternatively,
(ii) as a form of knowing (see, in particular, Sellars, 1956). On the
former view, being aware of a sense-datum is an extensional relation;
the subject is related by awareness to a real entity that has concrete
(as opposed to abstract) existence. On this view, being aware of a
sense-datum is not a form of knowledge; it is more like a state of
raw, unconceptualized sensation. The emphasis is simply upon the
qualitative nature of phenomenal experience. But, on the alternative
interpretation, the awareness of sense-data as a treated as a
cognitive state or process, in which the mind attends to and grasps
what is immediately before it, in a manner that somehow involves a
classification into kinds. On this later epistemic view, the awareness
of a sense-datum seems to require the exercise of concepts of at least
a low-level kind.
Russell was happy to classify the direct awareness relation of the
mind to a particular existing object as knowledge. This form of
knowledge was not considered by Russell to be propositional, although
it did involve attention (Russell, 1914). However, if the view is
taken that all knowing involves classification, and hence the use of
concepts, the issue is not so clear, as C. I. Lewis pointed out in
presenting an alternative to the sense-data account, a neo-Kantian
dual-component view of experience (Lewis, 1929). If the fact that
something seems red to me is accounted for by my having knowledge by
awareness of a red visual sense-datum, this suggests that I am aware
of it as red, and this seems to require that I have the concept of
redness. Equally, for a subject to attend to a particular entity
suggests that the subject is able to single out that entity out by
virtue of being aware of certain of its properties, which seems again
to require the use of sortal concepts, so that the subject can
conceive of the object as a unity.
According to Wilfrid Sellars (1956, Part I), the classical sense-data
theorists' conception of awareness (or acquaintance) is an amalgam of
two different lines of thought: first, that there is some phenomenal
or sensory aspect that distinguishes states of perceiving or seeming
to perceive from states of merely believing or thinking, and second,
that there are non-inferential knowings, knowings not based
immediately on any particular prior beliefs, which operate as the
foundation or evidence for all other empirical claims. In order to
begin to clarify the distinct issues involved, Sellars holds that we
need to distinguish more clearly between (a) the phenomenal or sensory
aspects presented in experience, and (b) the concepts (perhaps of a
low-level sort), inclinations to form beliefs, and other intentional
aspects of experience.
These points about the distinction between the phenomenal and
conceptual aspects of experience are connected with the interpretation
of the awareness of a sense-datum as a two-place relation between act
and object, albeit an act of a non-intentional kind connecting two
existing relata. In some manner knowledge originates in, and is
intimately tied up with the conceptual aspects of perceptual
experiences. Having a perceptual experience usually leads to a
"perceptual thought," an intentional state. Yet this fact does not
necessarily imply that the phenomenal aspect of perceptual experience
should itself be analyzed on the model of intentional acts, such as
thoughts about states of affairs. Many of the objections listed above,
particularly those pertaining to the internal coherence of the notion,
stem from the conflation of sensing and knowing – a "mongrel"
conception, as Sellars describes it, in which phenomenal consciousness
is equated directly with conceptual consciousness (Sellars, 1956, Part
I).
A related issue is the problem of how the term "immediately" is to be
understood in attempts to explicate the notion of sense-data. The term
is sometimes understood in a psychological sense, as connected with
how things appear from a subjective point of view. The idea is that
sense-data may be viewed as "immediate objects" of perception, in the
sense that awareness of them is not inferred from any belief, and that
sense-data, as defined, have a fixed small set of qualities. But then
it can be objected that the sense-data view is simply false to
experience: what I am usually immediately aware of when I look at an
apple is just the apple itself, and not a simply a patch of color with
a certain shape (Heidegger, 1968; Firth, 1949, 1950; Valberg, 1993).
It is the notion of there being an apple in front of me that springs
immediately to my mind when I see it – my mind is occupied with
concepts relating to the physical object framework. Discerning the
actual complex pattern of color and shape given to me in experience is
something that requires special training and attention. Similar
criticisms affect the closely related attempts to introduce the notion
of sense-data by appeal to ideas such as certainty or indubitability
(Price, 1932).
If the awareness of sense-data in itself is not a conceptual or
propositional state, the question of inference or otherwise does not
arise. A perceptual belief about the kind of object experienced would
simply be causally related to a prior state of phenomenal
consciousness. So, for example, it might be claimed that the
non-conceptual awareness of a sense-datum prompts the subject to form
a thought about the kinds of properties they are experiencing. If,
alternatively, awareness is construed as propositional in nature, then
this seems to undermine the original conception of sense-data as
accounting for the distinctive phenomenal, or sensory, aspects of
experience.
6. Responses to the Underlying Tensions
Many of the major subsequent developments in the philosophical
treatment of perceptual experience can be seen as attempts to grapple
with the tensions in the original notions of sense-data. Different
lines of thought have been developed, according to which particular
problem has been considered most pressing. There are four important
approaches to the question of how perceptual experience should be
analyzed that are particularly worthy of note.
a. Direct Realism and Disjunctivism
In recent times a number of philosophers have rejected the homogeneity
assumption. They argue that there is no single common type of
presented entity in veridical, illusory and hallucinatory experiences.
A claim of the form: "It looks to subject S as if there is an F
present…" can be made true by virtue of two quite different
situations. The objects that perceiving subjects are immediately
acquainted with in normal veridical perception are just the very
physical objects that common sense tells us exist. There are no other
entities involved as perceptual intermediaries. In other kinds of
case, such as hallucinations, and possibly also illusions, there may
be non-physical entities present in consciousness that are in some
sense qualitatively similar to physical objects, but this subjective
fact does not mean that there is a deeper similarity at the
ontological level. In refusing to allow any role for perceptual
intermediaries in the normal case, this view amounts to the general
theory of perception known as Direct Realism: veridical perception is
understood to comprise a direct relation of awareness between a
conscious subject and an object or feature of the external physical
world. The perceptual experience of a physical object is a "simple
relation" holding between subject and object (see, for example, Barnes
1940; Dretske, 1969; and Campbell, 2002). In virtue of its denial of a
"highest common factor" shared by different kinds of experiences (see
above, section 3d), Direct Realism has also been described as a form
of "Disjunctivism," although this latter term can have other
connotations in connection with theories of perception (see Snowdon,
1980; and also Martin, 2002).
Direct Realism involves a rejection of the Causal Theory of
Perception, where the latter theory is understood as attempting to
reductively analyze perceiving into separate components, involving an
experience that is logically distinct from (though causally related
to) the object perceived. The Direct Realist view, however, still
encounters the remaining two problems for the sense-datum theory
highlighted above. In particular, clarification is required of nature
of the non-causal simple relation of awareness that holds in the
normal perceptual case. How does an external physical object, by
virtue of causally connecting with the subject's sensory systems, come
to stand in a relation to the subject's consciousness, in such a
manner that the perceiver is made immediately aware of phenomenal
qualities belonging to that object? In the absence of a positive
account, the simple perceiving relation remains obscure, and the
grounds for introducing it are unclear (Coates, 1998 and 2007). A
further problem for this view is to make sense of the phenomenal or
sensory similarity between the entities that occur in hallucinations
and the objects that we are aware of in illusions and ordinary
perception. We need to account for the fact that the sense-data which
occur in hallucinations have phenomenal qualities that resemble those
which occur in the direct perception of the sensible properties of
physical objects. This problem becomes the more acute, to the extent
that a scientific conception of objects and their properties is
accepted.
b. Adverbialism
In an attempt to avoid the difficulty in providing a satisfactory
explication of the nature of the awareness relation, it has been
argued that appearances should be should be construed "adverbially" as
states of the perceiving subject, rather than as involving a two-place
relation (Ducasse, 1952; Chisholm, 1957). According to this view, it
is more perspicuous to analyze certain types of statements, statements
apparently about sense-datum particular entities and their properties,
as implicit claims about the manner in which a subject experiences or
senses. The relational interpretation of appearances should be
abandoned.
According to this account, the awareness of an appearance of a certain
kind should be modeled on the awareness of pains – pains are not
distinct from experience, they are properties of experience. Whereas
Moore held that, in seeing a red rose, the subject is acquainted with
a red sense-datum that is distinct from the subject's act of
consciousness, on the adverbial view the sensation of red is construed
as a state of the subject's consciousness.
So a claim such as:
(a) S is aware of a red visual sense-datum
is to be analyzed by:
(b) S visually senses redly.
The idea is that (b) reveals more perspicuously the underlying logical
form of the original claim (a).
As sketched out in this simple model, however, the proposed analysis
is clearly defective. For we need to account for the way that more
complex patterns of appearances are to be analyzed.
Suppose:
(c) S seems to see one object that is red and round and another
distinct object that is blue and square.
For the sense-data theorist, there would be two sense-data involved,
corresponding to the two objects apparently seen, with analogous
properties; thus (c) would be analyzed along the lines of:
(d) S is aware of one sense-datum x that is red and round, and
another sense-datum y that is blue and square.
But the simple adverbial view is unable to solve the problem of what
"binds" the apparent properties together in the complex appearance
presented to the subject. The only analysis forthcoming is:
(e) S visually senses redly and roundly and bluely and squarely
yet analysis (e) fails to distinguish between the initial appearance
(c) above, and the quite different overall appearance, where the links
between the properties are changed:
(f) S seems to see one object which is red and square and another
object that is blue and round
Hence the adverbial view must at a minimum allow a subdivision of the
contents of the subject's mind into distinct states of sensing
(Jackson, 1977; see also W. Sellars, 1982). So (c) now becomes
analyzed as involving a state1 of sensing redly and roundly, and a
distinct state 2 of sensing bluely and squarely. State 1 and state 2
should be construed as different aspects of a single subject, or as
co-constituents in the subject's mind. However, in whatever precise
form the adverbial view is developed, it still leaves unresolved the
issue of the way in which concepts are involved in perceptual
experience.
c. The Intentionalist Analysis of experience
One other important development that took place towards the end of the
twentieth century concerned what has become known variously as the
representationalist view of experience, or as the intentional view (or
intentionalism). This amounts to interpreting experience as a unitary
representational state; seeing, hearing, etc, are fully intentional
states whose structures in some way parallel that of thinking and
desiring. The acts of awareness or sensing are interpreted no longer
as involving relations to non-abstract existing entities, but are
instead understood as involving special attitudes towards states of
affairs that may or may not exist.
One extreme reductive version of this view was put forward by D.
Armstrong (1961), who tried to analyze perceiving purely in terms of
the acquisition of beliefs and inclinations to believe. An alternative
non-reductive version was advanced originally by Anscombe (1965), and
has been taken up in various forms subsequently by a number of
writers. On this version, the phenomenal content of perceptual
experience is distinguished from the intentional content of thoughts
and beliefs, but is still understood to be intrinsically
representational. For Anscombe, and others who adopt this view,
experiences represent facts in a special sensory manner. A question
such as, "What did the subject see?" can be interpreted either
extensionally, as asking about the actual physical object seen – the
material object – or intensionaly, as concerned with the way in which
things looked to the subject. When we describe how things look to the
subject, we characterize the content of the perceptual experience by
reference to the subject's viewpoint, and such descriptions need not
be true of the material object, which is physically present in front
of the perceiver. So the descriptions involved give the intentional
object of sensation, but need not refer to any actual existing item.
The intentional object of sensation has no more reality than the
fictional object of thought that is involved in my thought about
"Zeus." Something like this intentionalist interpretation of
experience has been associated with an alternative form of
Disjunctivism (McDowell, 1982, 1986 and 1998; Snowdon, 1980; Harman,
1990, and many other authors).
A major problem for this view is to give a satisfactory account of the
difference between the content of an experience such as: "seeming to
see that there is something white nearby," and the parallel thought:
"thinking that there is something white nearby," which has the same
intentional content, describable in identical terms. I can seem to see
that there is something white in front of me, and I can think that
there is something white in front of me; when I compare the two
states, I am subjectively aware that there is a vivid difference in my
consciousness, even though I am representing the same states of
affairs. If experiences and thoughts can have completely matching
contents, there must be some further, independent feature of my
consciousness in virtue of which they differ. It is not clear whether
the representational view really does justice to the way in which
experiences involve phenomenal or sensory qualities actually present
in consciousness.
Some writers claim that the representational content of experience is
non-conceptual, meaning that the subject need not exercise the
concepts necessary to characterize the experiences they have (Tye,
1995 and 2000). There is an important ambiguity here in the term
"non-conceptual." This can be understood in something like functional
terms, as relating to the way such states guide primitive or
semi-automatic actions in creatures lacking fully conceptual states –
in which case a nonconceptual state can be distinct from the
phenomenal character of experience, and cannot help to explain the
nature of the later. Alternatively, "non-conceptual" can be understood
as relating to phenomenal consciousness, the feature that makes the
difference between mere thought and experience. But then it is of no
help simply to be told that this feature is representational in a
nonconceptual sense – we are still stuck with the problem that the
representational contents of experience and thought can in some cases
match, and what has to be explained is the nature of the difference
between them. We require an account of the difference between the way
that perceptual content represents and mere thought represents. It is
arguable that the difference between them involves some intrinsic
phenomenal aspect of consciousness, something actually present in
experience that has more reality than a merely fictional object like
"Zeus." As Geach notes, sensations have formal as well as
representational properties (Geach, 1957, section 28). It is not clear
that the parallel between perceptual experience and thought has been
successfully made out on the intentionalist view (compare also Martin
2002).
7. Critical Realism
A final possibility that has been canvassed is some form of
dual-component analysis of perceptual consciousness, which attempts to
do justice to both the phenomenal (or sensory) aspects, and also the
conceptual aspects involved in experience. Perceptual experience is
analyzed as involving two quite different components: an intentional
component involving the representation of the subject's surrounding
environment through the exercise of classificatory concepts (perhaps
of a low-level kind), and a further non-intentional and non-conceptual
phenomenal state, in virtue of which phenomenal qualities are made
present in the subject's experience. Although the phenomenal
non-conceptual component is not understood as intrinsically
representational in the way that a thought is, it can still be treated
as in a weak sense representational; that is, the different aspects of
the phenomenal component of experience can still be described as
carrying informational content about those features of the environment
that normally cause them to arise in the subject's experience, and are
thus identified by reference to physical states of affairs.
A dual component view can take many different forms. Indeed,
acceptance of it is implicit on some versions of direct and naïve
realism. But of course it can also be combined with versions of the
Causal Theory of Perception, in which the subject's whole experience
is held to be in an important sense distinct from the object
perceived. One leading exponent of this view was Wilfrid Sellars, who
developed the Critical Realist view originally put forward by the
group that included his father Roy Wood Sellars, G. Santayana, and A.
O. Lovejoy (for the original statement of Critical Realism, see Drake
(ed.), 1920). Sense-data are re-interpreted as phenomenal or sensory
states of the subject; but this aspect is no longer analyzed as having
an act-object form. Sense-data awareness is replaced by a type of
one-place sensing state, a constituent or aspect of the subject's
mind, and such awareness does not involve a real relation between an
act and a distinct object. This sensing (or phenomenal) state causally
prompts a perceptual thought (or a "perceptual taking," involving low
level classification), which is an intentional state, directed on to
objects in the external world. The experience as a whole – involving a
phenomenal state, and also the exercise of concepts – is causally
related to the physical object perceived (W. Sellars, 1956, 1977,
1982).
The distinctive feature of the critical realist account is the claim
that the phenomenal aspect of experience guides perceptual thoughts
directly about the objects perceived; importantly, such perceptual
thoughts are not in normal cases of perception focused on the
phenomenal state – they refer directly to the physical objects we
think we see in our surroundings. In seeing an apple, I sense in a red
and round manner, and this guides my perceptual thought that there is
an apple in front of me. On this analysis of perception, the
sense-data theorist is viewed as guilty of a psychological error, as
well as a philosophical one: we do not form perceptual thoughts
directly about our own subjective phenomenal states. Entities with
some of the characteristics traditionally attributed to sense-data are
held to exist in experience, but they should not to be identified with
the objects of perception.
Sellars' own view was originally formulated in the context of a
complex overall account of the nature of language and the way in which
we come to refer to mental states such as thought and sensing, and
underwent important developments in later work. But an acceptance of
something like the central Critical Realist thought can be seen in the
work of many recent writers on perception (including, for example,
Grice, 1961; Mackie, 1976; Millar 1991; and Lowe, 1992). One problem
for the Critical Realist view consists in reconciling the duality of
experience posited by the account with the phenomenological sense that
there is a unity in experience. A second problem lies in showing how
the subject's perceptual judgments succeed in referring to objects
that are not immediately present in consciousness.
8. References and Further Reading
a. Books and Articles
* Anscombe, G. E. M., "The Intentionality of Sensation," in
Butler, R., (ed.) Analytical Philosophy: Second Series, Blackwell,
Oxford, pp. 158-180, 1965.
* Armstrong, D., Perception and the Physical World, Routledge, London, 1961.
* Austin, J. L., Sense and Sensibilia, Clarendon Press, Oxford, 1962.
* Ayer, A. J., Language Truth and Logic, Camelot Press, London, 1936.
* Ayer, A. J., Foundations of Empirical Knowledge, Macmillan, London, 1940.
* Ayer, A. J., "The Terminology of Sense-Data," Mind, 54, pp. 289-312, 1945.
* Ayer, A. J., The Problem of Knowledge, Macmillan, London, 1956.
* Ayer, A. J., "Has Austin Refuted the Sense-Datum Theory?,"
Synthese, 17, pp. 117-40, 1967.
* Barnes, W. F., "The Myth of Sense-Data," Proceedings of the
Aristotelian Society, 45, 1944.
* Berkeley, George, Principles of Human Knowledge, 1710.
* Berkeley, George, Three Dialogues Between Hylas and Philonous, 1713.
* Bermudez. J., "Naturalized Sense-data," Philosophy and
Phenomenological Research, 61, pp. 353-74, 2000.
* Brentano, F., Psychology From an Empirical Standpoint, Dunker
and Humblot, Leipzig, 1874.
* Broad, C. D., The Mind and its Place in Nature, Routledge and
Kegan Paul, London, 1925.
* Campbell, J. Reference and Consciousness, Clarendon Press, Oxford, 2002.
* Chisholm, R., Perceiving, Cornell University Press, Ithaca, 1957.
* Coates, P., "Perception and Metaphysical Scepticism,"
Supplementary Proceedings of the Aristotelian Society, 72, pp. 1-28,
1998.
* Coates, P., The Metaphysics of Perception, Routledge, London, 2007.
* Drake, D., (ed.), Essays in Critical Realism, Macmillan, London, 1920.
* Dretske, F., Seeing and Knowing, Routledge, London, 1969.
* Ducasse, C. J., Nature, Mind and Death, LaSalle, Illinois, 1951.
* Firth, R., "Sense-Data and the Percept Theory," Mind, 58 & 59,
1949/1950; reprinted in Swartz, R., (ed.) Perceiving, Sensing, and
Knowing, Doubleday, New York, pp. 204-270, 1965.
* Geach, P., Mental Acts, Routledge, London, 1957.
* Grice, H. P., "The Causal Theory of Perception," Supplementary
Proceedings of the Aristotelian Society, 35, pp. 121-52, 1961.
* Hanson, N. R., Patterns of Discovery, Cambridge University
Press, Cambridge, 1958.
* Harman, G., "The Intrinsic Qualities of Experience," in
Philosophical Perspectives, 4: Action, Theory and Philosophy of Mind,
1990.
* Heidegger, M., What Is Called Thinking?, tr. J. Glenn Gray,
Harper and Row, New York, 1968.
* Jackson, F., Perception: A Representative Theory, Cambridge
University Press, Cambridge, 1977.
* James, W., "The Sentiment of Rationality," Mind, 1897, reprinted
in his Essays on Pragmatism, Hafner Press, New York, pp. 3-36, 1948.
* Kirk, R., Raw Feeling, Oxford, Clarendon Press, 1994.
* Lewis, C. I., Mind and the World Order, Charles Scribner's Sons,
New York, 1929.
* Locke, John, An Essay Concerning Human Understanding, 1690; ed.
Nidditch, Clarendon Press, Oxford, 1975.
* Lowe, E., "Experience and its Objects" in Crane, T., (ed.) The
Contents of Experience, pp. 79-104, 1992.
* Mackie, J., Problems From Locke, Clarendon Press, Oxford, 1976.
* Martin, M. "The Transparency of Experience," Mind & Language,
17, pp. 376-425, 2002.
* Martin, M., "The Limits of Self-Awareness," Philosophical
studies, 120, pp. 37-89, 2004.
* Millar, A., Reasons and Experience, Clarendon Press, Oxford, 1991.
* Moore, G. E., "The Refutation of Idealism," Mind, 12, 1903;
reprinted in Moore, G. E., Philosophical Studies, 1922.
* Moore, G. E., "The Status of Sense-data," Proceedings of the
Aristotelian Society, 1913; reprinted in Moore, G. E., Philosophical
Studies, (1922).
* Moore, G. E., "Some Judgements of Perception," Proceedings of
the Aristotelian Society, 1918; reprinted in Moore, G. E.,
Philosophical Studies, 1922.
* Moore, G. E., Philosophical Studies, Routledge and Kegan Paul,
London, 1922.
* Merleau-Ponty, M., Phenomenology of Perception, tr. Colin Smith,
Routledge, London, 1945/1962.
* McDowell, J., "Criteria, Defeasibility and Knowledge" in
Proceedings of the British Academy, 68, pp. 455-79, 1982.
* McDowell, J., "Having the World in View: Sellars, Kant, and
Intentionality," Journal of Philosophy, pp. 431-491 (The Woodbridge
Lectures), 1998.
* Paul, G., "Is there a Problem About Sense-data?" Supplementary
Proceedings of the Aristotelian Society, 15, pp. 61-77, 1936.
* Price, H. H., Perception, Methuen, London, 1932.
* Robinson, H., Perception, Routledge, London, 1994.
* Russell, B., The Problems of Philosophy, Oxford University
Press, Oxford, 1912.
* Russell, B., "The Relation of Sense-data to Physics," Scientia,
4, 1914; reprinted in Russell, B., Mysticism and Logic, Unwin Books,
London, 1917.
* Russell, B., "The Philosophy of Logical Atomism," 1918,
reprinted in Logic and Knowledge, Marsh, R., (ed.), Allen and Unwin,
London, 1956.
* Ryle, G., The Concept of Mind, Hutchinson, London, 1949.
* Sellars, W., "Empiricism and the Philosophy of Mind," in
Minnesota Studies in The Philosophy of Science, Vol. I: The
Foundations of Science and the Concepts of Psychology and
Psychoanalysis, Feigl, H. and Scriven, M., (eds) Minnesota University
Press, Minneapolis, 1956.
* Sellars, W., "Phenomenalism," in his Science, Perception and
Reality, Routledge and Kegan Paul, London, 1963.
* Sellars, W., "Some Reflections on Perceptual Consciousness," in
Selected studies in Phenomenology and Existential Philosophy, Bruzina,
R., and Wishire, B., (eds) Nijhoff, The Hague, pp. 169-185, 1977.
* Sellars, W., "Sensa or Sensings: Reflections on the Ontology of
Perception," Philosophical Studies, 41, pp. 83-111, 1982.
* Shaughnessy, B., The Will, Cambridge University Press, Cambridge, 1980.
* Shaughnessy, B., Consciousness and the World, Oxford University
Press, Oxford, 2000.
* Smith, D., The Problem of Perception, Harvard University Press,
Cambridge, Mass., 2002.
* Snowdon, P., "Perception, Vision, and Causation" Proceedings of
the Aristotelian Society, 81, pp. 175-92, 1980.
* Sprigge, T., Facts Words and Beliefs, Routledge, London, 1970.
* Tye, M., Ten Problems of Consciousness, MIT Press, Cambridge, Mass., 1995.
* Tye, M., Consciousness, Color and Content, MIT Press, Cambridge,
Mass., 2000.
* Urmson, J. O., Philosophical Analysis, Oxford University Press,
Oxford, 1956.
* Valberg, J., The Puzzle of Experience, Clarendon Press, Oxford, 1992.
* Williams, M., Unnatural Doubts, Princeton University Press,
Princeton, 1996.
* Wittgenstein, L., Philosophical Investigations, Blackwell, Oxford, 1953.
b. Useful Collections Including Papers on Sense-Data
* Crane, T., (ed.), The Contents of Experience, Cambridge
University Press, Cambridge, 1992.
* Dancy, J., (ed.), Perceptual Knowledge, Oxford University Press,
Oxford, 1988.
* Hirst, R. J., (ed.), Perception and the External World,
Macmillan, New York, 1965.
* Schwartz, R., (ed.), Perception, Blackwell, Oxford, 2004.
* Swartz, R. J., (ed.), Perceiving, Sensing, and Knowing,
Doubleday, Anchor, New York, 1965.
* Warnock, G. J., (ed.), The Philosophy of Perception, Oxford
University Press, Oxford, 1967.
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