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V.
Plato himself, moreover, was a better judge of the value of his argument than his followers, and so was not unaware of the incomplete character of his dialectical victory over the bare dictum of Protagoras. He realizes plainly that in order to justify his rejection of it, it is incumbent on him to devise a tenable theory of Error. For even ‘subjectivism’ cannot be refuted by more scepticism, and even a rationalistic theory of knowledge is bound to discover some difference between ‘truth’ and ‘error’. This implication of his logical position, was not, of course, a thing to make too dangerously prominent, but it is clearly the meaning of the remark in 190 E, that ‘if we cannot show that false opinion is possible, we shall be obliged to admit many absurd things’. The ‘many absurd things’ are the Protagorean view of Truth as it has been interpreted by Plato. And the connexion between it and a failure to solve the problem of Error is this: if the possibility of Error cannot be explained, there can be no ‘false opinion’: and if there can be no ‘false opinion’ then all opinions are true; but this was precisely what Protagoras had meant, according to Plato. Hence the Platonic inquiry is on its own showing in the awkward position of being bound to discover a tenable theory of Error in order to save itself from a relapse into a Protagorean ‘subjectivism,’ which it has itself rashly declared to be equivalent to an abolition of all truth.
Nor does the fact that the Platonic interpretation of Protagoras is wrong, in any way relieve the logical pressure upon Plato’s intellectualism at this point. For as an ad hominem refutation, a failure to devise a theory of Error tells against Plato’s theory in any case. Whether or not Protagoras had really denied the possibility of Error, Plato’s theory of knowledge must irremediably collapse, if it cannot account for the existence of Error. And, unlike many modern intellectualists, who seem to contemplate with equanimity their total failure to discriminate between truth and error and to regard it as quite an unimportant defect in a theory of knowledge, Plato saw this clearly.
Hence the zeal and perseverance with which the inquiry
