What is time? Speusippus’ and Xenocrates’ reinterpretation of Plato’s Timaeus 37d

Speusippus and Xenocrates, the first two Heads of the Platonic Academy after Plato’s death, mainly take their cue from Timaeus to elaborate their philosophical systems from a pre-eminently mathematical point of view. Both are credited with the allegorical reading of the Timaeus, i.e. they use the fictitious narrative of chronological anteriority to explain the ontological priority of metaphysical principles. Anyway, the definitions of time attributed to them differ considerably from one another and the one of Plato: whereas by Plato, time is «an everlasting likeness moving according to number» (Tim. 37d6-7), for Speusippus it is «quantity in motion» (τὸ ἐν κινήσει ποσόν) (fr. 93 IP) and for Xenocrates time is «a measure of what is generated, and (also) everlasting motion» (μέτρον τῶν γενητῶν, καὶ κίνησιν ἀίδιον) (F. 79 IP). The two definitions remain isolated accounts and are usually not analysed and explored within the overall philosophical systems of Speusippus and Xenocrates by most scholars. My aim in this article is to explore what these two definitions of time have to do with the constitution of the cosmos and how, based on the different systems developed by the scholarchs, they recast the main aspects of the Platonic Timaeus, such as the world soul, the figure of the demiurge, and the principles of reality.