Category: identity
Type: puzzle
Associated thinker(s): Chrysippus (as reported by Philo)
Original publication or approximate period: Ancient Stoic puzzle attributed to Chrysippus; preserved in Philo, On the Eternity of the World §§48–49
Difficulty: Intermediate
Themes: coincidence, parts and wholes, ancient metaphysics
Related experiments: Lumpl and Goliath: The Statue and the Clay; Ship of Theseus; The Problem of the Many (Tibbles the Cat)
In the Stanford Encyclopedia of Philosophy’s version, Dion is a whole human being and Theon is the part of Dion consisting of everything except his right foot. If that foot is removed, Theon’s parts seem unchanged, so Theon appears to survive. If Dion survives too, they now occupy the same place, despite having seemed distinct before.
Philo of Alexandria’s later report gives a Chrysippean answer: Dion survives and Theon perishes, because two specifically qualified individuals cannot occupy the same substance. Philo immediately objects that this is paradoxical: Theon lost no part, while Dion lost a foot.
When a part is removed, which objects survive—and what assumptions about parts, identity, and coincidence determine the answer?
The puzzle tests whether every possible remainder of an object should count as an object in its own right. It also presses on how things can survive losing parts, a question that recurs in modern debates about material constitution.
Chrysippus’s reported answer is that Dion survives and Theon does not; Philo preserves and criticizes this reply. A modern response associated with Peter van Inwagen denies that Theon exists as an object before the operation: the relevant simples then constitute only part of Dion’s life. After the foot is removed, their activity constitutes a life, and the simples compose Dion. Other views in the material-constitution debate allow distinct objects to coincide or revise claims about persistence and existence. These are later positions, not a settled interpretation of the ancient argument.
The puzzle is not mainly about medicine or whether a person can live after an amputation. It asks what objects exist and which persist. The ancient discussion is not preserved in Chrysippus’s own surviving text: Philo reports it centuries later and offers a critical response. The SEP’s version specifies the right foot; Philo’s account does not specify a side.
The SEP notes a later related puzzle, Geach’s Tibbles and Tib: a cat and the part consisting of everything except its tail. It resembles Dion and Theon, but it is not the ancient report itself.
The SEP attributes the puzzle to Chrysippus and presents Theon as the part of Dion excluding the right foot. Philo’s On the Eternity of the World §§48–49 is later testimony, not Chrysippus’s own surviving text; it records both a reply attributed to Chrysippus and Philo’s objection. Bowin discusses the report as cryptic and its interpretation as disputed. Modern positions here are a brief map of material-constitution views, not a claim of consensus. The Tibbles and Tib comparison is identified as a later related puzzle. This is an original educational explanation, not expert review or an exhaustive survey.
Research check: 2026-11-01. The sources and passage locations consulted for this review are recorded in the local evidence ledger. Additional questions are teaching prompts, not established historical variations.