Two literal quotations from Chrysippus’ On Possibles , preserved in Plutarch’s On the Contradictions of the Stoics , seem to contradict the Stoic thesis of the isotropy of the void. According to this thesis the void is an infinite undifferentiated expanse (a wide continuous area) whose center is marked by, and coincides with, the position of the world. Since there is nothing else outside the world, the cohesive force that pervades it is sufficient on its own to guarantee the quasi–indestructibility of the trans–cyclical διακόσμησις (i.e the fact that in the new cosmic cycle the διακόσμησις returns in a form identical to the one it had in the previous cosmic cycle) and the eternity of the οὐσία. Conversely, in these two quotations Chrysippus maintains that there is a central διαφορά equipped with causal force. This seems to imply the anisotropy of the void. Chrysippus’s view here is also at odds with another official Stoic thesis, i.e. that the incorporeal is causally inert. In this paper it will be argued that there is in fact no contradiction, because, in those two quotations, Chrysippus consciously develops a cosmological hypothesis in order to resolve a difficulty concerning the role of fire during the universal conflagration. Chrysippus’ solution to this difficulty belongs to modal logic and consists in distinguishing between the actual universe and the possible ones.