Thus, such a conflict and clash among the contradictory...

Thus, such a conflict and clash among the contradictory philosophical views were the cause of intellectual confusion and deep fear. The habit of disputation nourished that situation by means of ambiguities and invalid syllogisms which it provided to its disputant heroes. On the basis of such ambiguities and invalid syllogisms, these heroes denied the world by rejecting all the human intellectual principles as well as the sensible and intuitive propositions.

Gorgias,[^3] one of the prominent leaders of this school, wrote a book on non-existence. In this work, he tried to prove a number of points: (1) nothing exists; (2) if anything exists, one cannot know it; (8) if we assume that one can know it, one cannot communicate it to others. (p. 110) For quite a while, sophistry had expressed in various ways its disregard for philosophy and science, until Socrates, Plato and Aristotle emerged and held strong positions against it.

Aristotle laid down his well-known logic for discovering the sophistical fallacies and for organizing human thought. His epistemological doctrine may be summarized as follows. Sense knowledge and primary or secondary rational knowledge, which are acquired by taking into consideration logical principles, are truths with an absolute value. Due to this, Aristotle permits in demonstration (the absolute evidence in his logical sense) the use of both sense knowledge and rational knowledge.

Later, an attempt was made to reconcile the two opposite tendencies - that is, the tendency leaning toward absolute denial (sophistry), and the tendency asserting affirmation (Aristotelian logic). This attempt was represented in the skeptical doctrine thought to have been founded by Pyrrho[^4] who is known for his ten proofs for the necessity of absolute doubt. According to Pyrrho, every proposition can be stated in one of two ways: it can be either affirmed or denied with equal force.

But the doctrine of certitude finally prevailed in the philosophical field, and reason mounted the throne given to it by Aristotle, judging and making decisions while bound by the logical criteria. The fire of doubt died down for centuries, until around the sixteenth century when the natural sciences became active and made discoveries of unexpected truths, especially in astronomy and the general order of the universe.

These scientific developments were similar to the force of disputation in the Greek period.