Plato used mathematics extensively in his account of the cosmos in the Timaeus, but as he did not use equations, but did use geometry, harmony and according to some, numerology, it has not been clear how or to what effect he used mathematics. This paper argues that the relationship between mathematics and cosmology is not atemporally evident and that Plato’s use of mathematics was an open and rational possibility in his context, though that sort of use of mathematics has subsequently (...) been superseded as science has progressed. I argue that there is a philosophically and historically meaningful space between ‘primitive’ or unreflective uses of mathematics and the modern conception of how mathematics relates to cosmology. Plato’s use of mathematics in the Timaeus enabled the cosmos to be as good as it could be, allowed the demiurge a rational choice and allowed Timaeus to give an account of the cosmos. I also argue that within this space it is both meaningful and important to differentiate between Pythagorean and Platonic uses of number and that we need to reject the idea of ‘Pythagorean/platonic number mysticism’. Plato’s use of number in the Timaeus was not mystical even though it does not match modern usage. (shrink)

I have argued elsewhere that the idea that Aristotle aspired to improve the theories of the planetary motions of Eudoxus and Callippus by adding the ‘counteracting’ spheres (ἀνελίττουσαι) first emerged with the Peripatetic exegete Sosigenes in the second century CE. This paper supplements that argument by contrasting two major lines of interpretation of the astronomical system set out in Metaphysics Λ.8: Adrastus of Aphrodisias’ widely ahistorical account, and Sosigenes’ attempt to save Aristotle against later developments of astronomical science.

L’article met en lumière la continuité intellectuelle de l’Académie à propos d’une question précise, les rapports entre philosophie et géométrie. On soutient d’abord que, dans les livres VI-VII de la République, Platon ne cherche pas à réformer les pratiques des géomètres mais identifie les contraintes incontournables de leurs raisonnements (constructions, hypothèses), qui constituent et limitent leur objectivité. On montre ensuite que cette analyse constitue le cadre des réflexions académiciennes ultérieures sur la géométrie. Speusippe reprend et développe l’analyse platonicienne des constructions (...) géométriques, qui est appliquée (de Speusippe à Crantor) à la cosmologie et même à la doctrine des principes, afin d’expliquer comment elles saisissent leurs objets éternels depuis le devenir, de manière indirecte. Si la Nouvelle Académie d’Arcésilas et de Carnéade critique les mathématiques, on fait l’hypothèse qu’il s’agissait pour elle – dans le contexte des débats philosophiques hellénistiques sur les usages des mathématiques –, de rappeler les limites de leur objectivité contre toute idéalisation dogmatique de la méthode géométrique. (shrink)