Journal of the History of Philosophy

The Logical Background of Plato's Writing MAURICE COHEN MANYPASSAGESIN GREEKWRITING before, or at most contemporaneous with, the presumed period of Plato's earliest dialogues ~ make plausible the hypothesis that in his early dialogues Plato is deliberately generating and directing fallacies of ambiguity and form. Even a brief survey of textual references to deliberately misleading argumentation, problems of meaning, and deliberate puzzles, and of evidence for the critical use of deductive techniques indicates that a philosophically significant degree of semantic and deductive skill is present in writers before Plato. This paper consists of such a survey in which I present and discuss textual evidence of fifth-century (a) awareness of problems of meaning and (b) skill in deductive reasoning. I must emphasize that this review is not intended as a contribution to a systematic history of logic, but rather as a critical overview of passages relevant to Plato's logical techniques, particularly in the early aporetic dialogues. In keeping with Plato's own wide-ranging interest in literature, history, and science, as well as philosophy, I have not hesitated to present a diversity of texts, choosing in every case, however, from works that Plato can reasonably be assumed to have known. For the sake of brevity, I have avoided discussing at length texts requiring intensive technical analysis or critical reconstruction; hence the summary treatment---despite their indubitable importance to a more detailed discussion--of Parmenides' poem and Zeno's paradoxes,~ and the absence of discussion of Hippocrates of Chios' quadrature of lunes, the only surviving fifthcentury geometric proof.' The twofold classification of (a) evidence of awareness of problems of meaning and (b) evidence of deductive skill in non-mathematical C. 400; for a summary of discussions about the presumed beginning of Plato's activity as a writer of dialogues, cf. Sir David Ross, Plato's Theory of Ideas (Oxford: Clarendon Press, 195]), p. 4. See below, sec. V. The most important text on Hippocrates of Chios is Simplicius' extract from Eudcmus on Hippocrates' quadrature of lunes. See Sir Thomas Heath, ,4 History of Greek Mathematics , Vol. I: From Thales to Euclid (Oxford: Clarendon Press, 1921), pp. 183-200, for a survey of the extensive critical literature on this text and Hcath's own interpretation and analysis. Heath gives a shorter version of his reconstruction of Hippocrates' proof in Euclid's Elements (2rid. edn.; New York: Dover Publs., 1956), I, 387. 112 HISTORY OF PHILOSOPHY reasoning is intended to encourage logical analysis of Plato's dialogues in terms of the traditional classification of fallacies into fallacies of ambiguity (in dictione) and fallacies of form (extra dietionem)." I believe that even the minimal textual evidence presented here of fifth-century awareness of problems of meaning indicates that in the early dialogues Plato could easily have avoided fallacies of ambiguity, while the evidence of deductive sophistication proves that he could have avoided fallacies of form. A fuller survey, taking into account the orators, and critical reconstructions of the proof techniques of fifth-century mathematics and of the Sophists' grammatical and logical studies,' would only strengthen the probability that conspicuous fallacies in the early dialogues are deliberate on Plato's part. Particularly after about 440 B.c., many writers present criticisms of the imputed social and moral consequences of supposedly excessive interest in what we would call today verbal and logical manipulation. Just Logos' criticisms of Unjust Logos in Aristophanes' Clouds," which will shortly be examined in some detail,' is an obvious example of such criticisms; far more savage are Cleon's opening remarks in his speech against the Mytilenians in Thucydides' history: I wonder also who will be the man who will maintain the contrary, and will pretend to show that the crimes of the Mytilenians are of service to us, and our misfortunes injurious to the allies. Such a man must plainly either have such confidence in his rhetoric as to adventure to prove that what has been once for all decided is still undetermined, or be bribed to try to delude us by elaborate sophisms. In such contests the state gives the rewards to others, and takes the dangers for herself. The persons to blame are you who are so foolish...