III. Theory of Knowledge
The Pre-Socratics had turned all their attention to the physical world (cosmology) and in a diversity of opinions they (with the exception of Democritus) had shown that the world has a divine origin. In this search, man, even if he had not been completely passed over, had been considered as one of the many phenomena of the physical world.
The disagreement among philosophers who had not succeeded in establishing what had been the germ element or elements of the world, and the changed conditions of the time combined to direct the attention of philosophers away from the object and toward the subject, from the world to man, from cosmology to psychology.
The Sophists were the first to show complete indifference to the problem of the world of matter and to center their efforts upon man. But man can be an object of study in his sense knowledge as well as in that more profound one of reason. The Sophists stopped at the first, at the immediacy of sense impressions. (The analysis of reason was reserved to Socrates and his disciples.)
The Sophists stopped at the data of experience, at empirical and not rational knowledge, and from this point of view they wished to judge the world of reality. With them was born relativism of knowledge and Skepticism: the man-measure of Protagoras, and the "nothing exists" of Gorgias.
In the fragment of Protagoras which Plato has preserved for us, it is stated:
"Man is the measure of all things, of those that are in so far as they are,
and those that are not in so far as they are not."
From this he deduces that the subjective phenomena of our sensations become judges of reality. There is no reality of itself, but only reality as it appears to us:
"Man is the measure of what exists."
Thus to two different individuals the same reality can appear in opposite aspects; e.g., air is hot for one, cold for another; both sensations are true and both denote states of reality. Everything is relative. Reality being thus reduced to the subjectivism of experience, it was easy to make the transition of Gorgias to complete Skepticism.
"Nothing exists," said Gorgias; "if something does exist, we cannot know it; if we come to know it, we cannot teach it to others." This transition from the relativism of Protagoras to Skepticism seems logical. If reality is relative to the knowledge of empirical data, there is no reality of itself. Hence nothing exists. If it should exist, it would be impossible for it to be known by us as it is in itself, because we can be witnesses only of the impressions in their sensible immediacy, and no one assures us that this is representative of reality. Nor can we teach others what we know, since everyone has a different manner of feeling, and the manner of feeling of the master is not the same as that of his students.
Hence the only thing remaining is the use of the word, and Gorgias affirmed that all things can appear true and just, if oratorical power is capable of revealing things as true and just, beyond every pretension of reality of content.