Theaetetus | Page 7

been already asked and indirectly answered in the Meno: 'How can a man be ignorant of that which he knows?' No answer is given to this not unanswerable question. The comparison of the mind to a block of wax, or to a decoy of birds, is found wanting.
But are we not inverting the natural order in looking for opinion before we have found knowledge? And knowledge is not true opinion; for the Athenian dicasts have true opinion but not knowledge. What then is knowledge? We answer (3), 'True opinion, with definition or explanation.' But all the different ways in which this statement may be understood are set aside, like the definitions of courage in the Laches, or of friendship in the Lysis, or of temperance in the Charmides. At length we arrive at the conclusion, in which nothing is concluded.
There are two special difficulties which beset the student of the Theaetetus: (1) he is uncertain how far he can trust Plato's account of the theory of Protagoras; and he is also uncertain (2) how far, and in what parts of the dialogue, Plato is expressing his own opinion. The dramatic character of the work renders the answer to both these questions difficult.
1. In reply to the first, we have only probabilities to offer. Three main points have to be decided: (a) Would Protagoras have identified his own thesis, 'Man is the measure of all things,' with the other, 'All knowledge is sensible perception'? (b) Would he have based the relativity of knowledge on the Heraclitean flux? (c) Would he have asserted the absoluteness of sensation at each instant? Of the work of Protagoras on 'Truth' we know nothing, with the exception of the two famous fragments, which are cited in this dialogue, 'Man is the measure of all things,' and, 'Whether there are gods or not, I cannot tell.' Nor have we any other trustworthy evidence of the tenets of Protagoras, or of the sense in which his words are used. For later writers, including Aristotle in his Metaphysics, have mixed up the Protagoras of Plato, as they have the Socrates of Plato, with the real person.
Returning then to the Theaetetus, as the only possible source from which an answer to these questions can be obtained, we may remark, that Plato had 'The Truth' of Protagoras before him, and frequently refers to the book. He seems to say expressly, that in this work the doctrine of the Heraclitean flux was not to be found; 'he told the real truth' (not in the book, which is so entitled, but) 'privately to his disciples,'--words which imply that the connexion between the doctrines of Protagoras and Heracleitus was not generally recognized in Greece, but was really discovered or invented by Plato. On the other hand, the doctrine that 'Man is the measure of all things,' is expressly identified by Socrates with the other statement, that 'What appears to each man is to him;' and a reference is made to the books in which the statement occurs;--this Theaetetus, who has 'often read the books,' is supposed to acknowledge (so Cratylus). And Protagoras, in the speech attributed to him, never says that he has been misunderstood: he rather seems to imply that the absoluteness of sensation at each instant was to be found in his words. He is only indignant at the 'reductio ad absurdum' devised by Socrates for his 'homo mensura,' which Theodorus also considers to be 'really too bad.'
The question may be raised, how far Plato in the Theaetetus could have misrepresented Protagoras without violating the laws of dramatic probability. Could he have pretended to cite from a well-known writing what was not to be found there? But such a shadowy enquiry is not worth pursuing further. We need only remember that in the criticism which follows of the thesis of Protagoras, we are criticizing the Protagoras of Plato, and not attempting to draw a precise line between his real sentiments and those which Plato has attributed to him.
2. The other difficulty is a more subtle, and also a more important one, because bearing on the general character of the Platonic dialogues. On a first reading of them, we are apt to imagine that the truth is only spoken by Socrates, who is never guilty of a fallacy himself, and is the great detector of the errors and fallacies of others. But this natural presumption is disturbed by the discovery that the Sophists are sometimes in the right and Socrates in the wrong. Like the hero of a novel, he is not to be supposed always to represent the sentiments of the author. There are few modern readers who do not side with Protagoras, rather than with Socrates, in the dialogue which is called by his name. The Cratylus presents a similar difficulty: