The Stoic Criterion of Identity

The story starts with a scene from an early Greek comedy. Its author is the Syracusan comic playwright Epicharmus, and it probably dates from the opening decades of the fifth century B.C. The following reconstruction is based on one verbatim quotation of twelve lines, plus two indirect references to it in later authors.' Character A is approached by Character B for payment of his subscription to the running expenses of a forthcoming banquet. Finding himself out of funds, he resorts to asking B the following riddle: 'Say you took an odd number of pebbles, or if you like an even number, and chose to add or subtract a pebble: do you think it would still be the same number?' 'No,' says B. 'Or again, say you took a measure of one cubit and chose to add, or cut off, some other length: that measure would no longer exist, would it? 'No.' 'Well now,' continues A, 'think of men in the same way. One man is growing, another is diminishing, and all are constantly in the process of change. But what by its nature changes and never stays put must already be different from what it has changed from. You and I are different today from who we were yesterday, and by the same argument we will be different again and never the same in the future.' B agrees. A then concludes that he is not the same man who contracted the debt yesterday, nor indeed the man who will be attending the banquet. In that case he can hardly be held responsible for the debt. B, exasperated, strikes A a blow. A protests at this treatment. But this time it is B who neatly sidesteps the protest, by pointing out that by now he is somebody quite different from the man who struck the blow a minute ago. To subsequent generations, the argument used in this scene read like a remarkable anticipation of a philosophical doctrine associated with the names of Heraclitus and Plato, that of the radical instability of the physical world; and Plato himself was pleased to acknowledge such evidence of the doctrine's antiquity.2 But although the puzzle is a serious challenge to ordinary assumptions about identity, never in the fourth century B.C., the era of Plato and Aristotle, does it meet with a proper philosophical analysis