(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?