to tradition, the sixth-century B.C.philosopher Thales
of Miletus introduced geometry and astronomy to
Greece after visiting Egypt. He may also have encoun-
tered there the idea that the universe was based ulti-
mately upon water. But Greek thought was unlike that
of the Egyptians in several important respects. Perhaps
because of the structure of their language, the Greeks
sought from the beginning to demonstrate the logical
connection between statements in the clearest possible
way. This in turn forced them to confront the problem
of epistemology, or how what is known is known.
These two issues, epistemology and the nature of the
physical universe, have remained among the central
concerns of Western thought.
Most Greek thinkers believed that the impressions
produced by the senses are deceptive. To be truly
knowable, something must be both permanent and ac-
cessible to thought. Thales, like most early philoso-
phers, assumed the essential unity and permanence of
all matter. The view of Heraclitus (c. 500 B.C.) that the
universe was in a state of perpetual movement at first
found little support, and much effort was expended on
determining the fundamental element or elements upon
which the universe was based. Eventually, Empedocles
of Acragas (c. 490–c. 430 B.C.) declared that four ex-
isted: earth, air, fire, and water. His theory was later ac-
cepted by Aristotle and formed the basis of most
physical speculation until the scientific revolution of
modern times. An alternative, proposed by Leucippus
of Miletus and his pupil Democritus, seemed less per-
suasive. It held that everything was composed of atoms,
invisible particles that combined and separated to pro-
duce the various forms of matter.
If these early philosophers speculated on ethical
matters, their writings on the subject have been lost,
but the proper conduct of life was vitally important to
people who lacked a moral code based on divine reve-
lation. Pythagoras, who founded a school at Croton in
Italy around the year 500 B.C., taught ethics based in
part on the cult of Orpheus. In the process he discov-
ered the mathematical basis of musical harmony and
decided that the fundamental organizing principle of
the universe was number. This idea, like his theory that
the Earth revolved around the Sun, would prove inter-
esting to later thinkers.
By the fifth century B.C., however, most people
learned their ethics and the practical arts of rhetoric
and persuasion from the Sophists. These itinerant
teachers charged high fees for their services but offered
nothing less than a prescription for success in private
and public life. Their teachings varied, but most were
subjectivists. As Protagoras, the most famous of them,
said: “Man is the measure.” He meant that the individ-
ual’s experience, however imperfect in an absolute
sense, is the only conceivable basis for knowledge or
judgment. Everything is relative.
The implications of such a view were profoundly dis-
turbing. Extreme Sophists held that truth was objectively
unknowable. Law and even the polis were based on con-
vention and mutual agreement, not fundamental princi-
ples. Some went so far as to claim that justice was merely
the interest of the strong and that the gods had been in-
vented by clever men as a means of social control. The
teachings of Socrates and of his pupil Plato were in-
tended in part to refute these ideas.
Socrates (c. 470–399 B.C.) wrote nothing. He wan-
dered about the streets of Athens asking questions that
revealed the underlying assumptions behind human
values and institutions. Using logic and irony, he would
then question the validity of those assumptions. His
purpose, unlike that of the Sophists whom he otherwise
resembled, was to find an objective basis for ethical and
political behavior. He made no promises and took no
fees, but his questions were rarely open-ended and
made people feel foolish.
The patience of the Athenians was severely tried.
In 399 B.C.they executed him for corrupting the youth
of Athens and inventing new gods. The charges were
largely specious, but they reflected something more
than public irritation. Socrates, though himself of hum-
ble origins, favored aristocracy as the ideal form of gov-
ernment and mocked the democratic notions then in
favor.
His views on other subjects are unknown, but Plato
(428–347 B.C.) made him the leading character in his
dialogues. As a young man from an aristocratic Athen-
ian family, Plato toyed with the idea of a political career
until the aftermath of the Sicilian expedition and the
execution of Socrates convinced him that politics was
incompatible with a good conscience. Around the year
387 B.C.he founded the Academy, a kind of institute
for advanced studies in mathematics, the physical sci-
ences, and philosophy.
Plato’s dialogues present philosophical arguments
in dramatic form. The Socrates character reflects the
author’s views. With the exception of the Timaeus,a later
dialogue that deals with cosmology and mathematics,
most explore questions of ethics, education, govern-
ment, and religion. The Republicdescribes the ideal
state, while the Protagorasargues against the Sophists.
Their underlying principle is the theory of forms.
Plato argued that the form of a thing has an objective
reality of its own. It is a “universal” or “idea” that can be
understood only by the intellect and that exists apart46 Chapter 3