Chrysippus on the Impossibility of Two Individuals in One Body

Abstract

In this paper I contend that the ancient Chrysippean puzzle of Dion and Theon which is understood as a puzzle of synchronic identity, can be understood differently from a common interpretation of it as an instance of the problem of the many. This interpretation first appeared in Sedley (1982), and continues to be the common one (see Carmichael 2020). In the puzzle, as reported by Philo, Chrysippus relies on a principle seeming to affirm that: no two individuals can occupy one body. The problem in the puzzle is rather that Chrysippus’ principle expresses a symmetric relation; as such it cannot itself account for the asymmetric result, which is that one individual displaces another individual from occupying the same body. This present paper does not account for the ordering of the displacement. But it makes an argument for why Chrysippus should have sought the conclusion he affirms; for it demonstrates that his materialism is sensitive to some changes being apparently qualitative rather than quantitative. In other words, the passage, when read carefully, is a sign of Chrysippus’s confidence in the sophistication of his own materialism, something that has been misdiagnosed by the literature on its interpretation as an instance of the problem of the many.