. In reality, the result of
this procedure is to rob the distinction between truth and falsehood
of all meaning. It makes no difference whether we say that all
opinions are true, or whether we say that all are false. The words
truth and falsehood, in such context, have no meaning. To say that
whatever I feel is the truth for me means only that what I feel I
feel. To call this "truth for me," adds nothing to the meaning.

Protagoras seems to have been led to these doctrines partly by
observing the different accounts of the same object which the
sense-organs yield to different people, and even to the same person at
different times. If knowledge depends upon these impressions, the
truth about the object cannot be ascertained. He was also influenced
by the teaching of Heracleitus. Heracleitus had taught that all
permanence is illusion. Everything is a perpetual becoming; all things
flow. What is at this moment, at the next moment is not. Even at one
and the same moment, Heracleitus believed, a thing is and is not. If
it is true to say that it is, it is equally true that it is not. And
this is, in effect, the teaching of Protagoras.

The Protagorean philosophy thus amounts to a declaration that
knowledge is impossible. If there is no objective truth, there cannot
be any knowledge of it. The impossibility of knowledge is also the
standpoint of Gorgias. The title of his book is characteristic of
{117} the Sophistical love of paradox. It was called "On Nature, or
the non-existent." In this book he attempted to prove three
propositions, (1) that nothing exists: (2) that if anything exists, it
cannot be known: (3) that if it can be known, the knowledge of it
cannot be communicated.

For proof of the first proposition, "nothing exists," Gorgias attached
himself to the school of the Eleatics, especially to Zeno. Zeno had
taught that in all multiplicity and motion, that is to say, in all
existence, there are irreconcilable contradictions. Zeno was in no
sense a sceptic. He did not seek for contradictions in things for the
sake of the contradictions, but in order to support the positive
thesis of Parmenides, that only being is, and that becoming is not at
all. Zeno, therefore, is to be regarded as a constructive, and not
merely as a destructive, thinker. But it is obvious that by
emphasizing only the negative element in his philosophy, it is
possible to use his antinomies as powerful weapons in the cause of
scepticism and nihilis