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AncientPre-socratic Philosophy

Greek philosophy began, around 600 B.C.E., with a series of attempts to specify the fundamental constituents of the universe. Questions soon began to be raised about the prospects for success in this enterprise. The poet-philosopher Xenophanes (c. 560–c. 478 B.C.E.) denied that knowledge—as opposed to belief or opinion—was possible, at least about the gods and the nature of the universe. However, since Xenophanes himself had much to say about gods, he must have considered some opinions more reliable than others; and other evidence seems to support this. Similarly, Democritus (c. 460–c. 370B.C.E.) expressed very serious doubts about our ability to know the real nature of things. But he too was the proponent of an ambitious cosmological theory—the original atomic theory—so he must have found room for some types of reasonable beliefs. He does speak of reason as superior to the senses, and able to go further than the senses alone. Yet he recognizes the need to rely on the senses as a starting point for inquiry, and this sets limits to how far anyone can repudiate the evidence they provide. How exactly he resolved this tension is debatable.


And as for what is clear, no man has seen it, nor will there be anyone

Who knows about the gods and what I say about all things;

For even if one should happen to say what has absolutely come to pass

Nonetheless one does not oneself know; but opinion has been constructed in all cases.

SOURCE: Xenophanes, fragment DK B34 (translation author's).

A sharp distinction between the senses and reason had earlier been drawn by Parmenides (born c. 515 B.C.E.), again to the detriment of the senses. But Parmenides also criticized those who relied on their senses as out of touch with true being, to which only pure reason can give access; the division between cognitive faculties is thus paralleled by a division between levels of reality—the ordinary world around us being stigmatized as less than fully real. This division is a prototype for Plato's distinction between purely intelligible Forms and the world perceived by the senses.

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