ground. Like the other notions of the earlier Greek philosophy, it was
held in a very simple way, without much basis of reasoning, and without
suggesting the questions which naturally arise in our own minds on the same
subject.

(b) The fixedness of impressions of sense furnishes a link of connexion
between ancient and modern philosophy. The modern thinker often repeats
the parallel axiom, 'All knowledge is experience.' He means to say that
the outward and not the inward is both the original source and the final
criterion of truth, because the outward can be observed and analyzed; the
inward is only known by external results, and is dimly perceived by each
man for himself. In what does this differ from the saying of Theaetetus?
Chiefly in this--that the modern term 'experience,' while implying a point
of departure in sense and a return to sense, also includes all the
processes of reasoning and imagination which have intervened. The
necessary connexion between them by no means affords a measure of the
relative degree of importance which is to be ascribed to either element.
For the inductive portion of any science may be small, as in mathematics or
ethics, compared with that which the mind has attained by reasoning and
reflection on a very few facts.

II. The saying that 'All knowledge is sensation' is identified by Plato
with the Protagorean thesis that 'Man is the measure of all things.' The
interpretation which Protagoras himself is supposed to give of these latter
words is: 'Things are to me as they appear to me, and to you as they
appear to you.' But there remains still an ambiguity both in the text and
in the explanation, which has to be cleared up. Did Protagoras merely mean
to assert the relativity of knowledge to the human mind? Or did he mean to
deny that there is an objective standard of truth?