Euclides (c. 430—360 BCE)

Euclides was a native of Megara, and founder of the Megarian or
Eristic sect. He applied himself early to the study of philosophy, and
learned from the writings of Parmenides the art of disputation.
Hearing of the fame of Socrates, Euclides moved to Athens and became a
devoted student for many years. Because of an enmity between Athenians
and Megarians, a decree was passed which forbid any Megarian from
entering Athens under the penalty of death. Euclides moved twenty
miles out of Athens, and would sneak into the city at night for
instruction, dressed as a woman in a long cloak and veil. He
frequently became involved in business disputes in civil courts.
Socrates, who despised forensic contests, expressed dissatisfaction
with Euclides for his fondness for controversy. It is likely that this
provoked a separation between Euclides and Socrates, for after this
Euclides was the head of a school in Megara which taught the art of
disputation. Debates were conducted with so much vehemence among his
pupils, that Timon said of Euclides that he carried the madness of
contention from Athens of Megara (Diog. Laert, 6:22). Nevertheless,
his restraint is attested to in a story about a quarrel he had with
his brother. His brother charged, "Let me perish if do not have
revenge on you." To this Euclides replied, "And let me perish if I don
not subdue your resentment by forbearance, and make you love me as
much as ever." In disputes Euclides was averse to the analogical
method of reasoning, and judged that legitimate argumentation consists
in deducing fair conclusions from acknowledge premises.

His position was a combination of Socraticism and Eleaticism. Virtue
is knowledge, but knowledge of what? It is here that the Eleatic
influence became visible. With Parmenides, the Megarics believed in
the one Absolute being. All multiplicity, all motion, are illusory.
The world of sense has in it no true reality. Only Being is. If virtue
is knowledge, therefore, it can only be the knowledge of this Being.
If the essential concept of Socrates was the Good, and the essential
concept of Parmenides Being, Euclides now combined the two. Thus,
according to Cicero, he defined the "supreme good" as that which is
always the same. The Good is identified with Being. Being, the One,
God, Intelligence, providence, the Good, divinity, are merely
different names for the same thing. Becoming, the many, evil, are the
names of its opposite, not-being. Multiplicity is thus identified with
evil, and both are declared illusory. Evil has no real existence. The
good alone truly is. The various virtues, as benevolence, temperance,
prudence, are merely different names for the one virtue, knowledge of
being. It is said that when Euclides was asked his opinion concerning
the gods, he replied, "I know nothing more of them than this, that
they hate inquisitive persons."