Abstract
In Part I of Plato's Theaetetus, three attempts are made to refute Protagoras' Measure Doctrine (MD). After the first "superficial" attempt, the second and the third follow and each of them is regarded as a successful refutation. This paper examines the third refutation, which raises the difficulty to retain MD in the case of future judgment. MD is widely considered to be an assertion of relativism, according to which 'true' is not an absolute predicate ('true') but a relative one ('true for'). Fine, however, takes MD to be an assertion, not of relativism, but of infallibilism, which takes 'true' to be absolute. A connection, however, can be established between relativism and infallibilism, if we distinguish sentences from the (possibly private) content of them and take relativism to concern the former and infallibilism the latter. What is the point of the third attempt? Is it that sometimes a contradiction follows from two temporarily separated judgment tokens? This is unlikely. For even if a contradiction really follows from them this is not particular to future judgment: the same argument could also be made for past and present judgment. It is clear, however, that the argument is meant to exploit something special to future judgment. Relativism can be extended to include a time scale, by relativizing 'true' not only to the judging subject but also to the moment when the judgment is made: thus the correct form of truth predicate becomes "p' is true for x at t'. It is inconceivable that Plato failed to recognize that on this extended relativism no contradiction follows from two temporarily separated judgment tokens. If we re-interpret extended relativism at the level of infallibilism, the content of the sentence becomes a function of the sentence(s), the judging subject(x) and the moment of the judgment(t): D (s, x, t). Take two judgment tokens made by S at t_1 and t_2 with the content D ('p', S, t_1) and D ('-p', S, t_2) respectively. We can assume that the latter contradicts D ('p', S, t_2). If we can show that D ('p', S, t_1) is identical to D ('p', S, t_2), we can refute MD. Protagoras of course will not admit the identity, and it seems very difficult to establish the identity without begging the question. To resolve this difficulty, Plato introduces the distinction between the first order good and the second order good. Examples are 'this tastes good' (judgment about the first order good) and 'this way of cooking will bring about the judgment 'this tastes good" (judgment about the second order good). Even if the truth of the former judgment depends entirely on (the occurrence of the) judgment itself, the truth of the latter depends not on the judgment itself but on the truth of the former. This interpretation explains the special role given to future judgment, because the judgment about the second order good has the form of 'something brings about something', which is essentially future judgment.
