An argument in Cicero's Tusculan Disputations (Tusc. 1.39–49) defends psychic immortality by reference to the physical constitution of the soul. This article argues that this ‘Physical Argument’ should be interpreted as a reception of Plato's doctrine of the soul within the philosophical paradigm of the Hellenistic era. After analysing the argument, it is shown that Cicero's proof recasts elements of Plato's Phaedo, in particular the kinship between the soul and the heavens and the soul's essentially contemplative nature, within a corporealist (...) cosmology. The article also argues that Cicero formulates his argument to oppose the Stoic view that the soul's survival after death is only temporary. The Physical Argument emerges as a modernization of Platonic thought, putting Plato into dialogue with contemporary Hellenistic philosophy. Cicero, too, emerges as a more adept philosophical author than is often supposed. (shrink)