Descartes claimed that he thought he could deduce the assumptions of his Meteorology by the contents of the Discourse. He actually began the Meteorology with assumptions. The content of the Discourse, moreover, does not indicate how he deduced the assumptions of the Meteorology. We seem to be left in a precarious position. We can examine the text as it was published, independent of Descartes’ claims, which suggests that he incorporated a presumptive or hypothetical method. On the other hand, we can take Descartes’ claims as our guide and search for the epistemic foundations of the Meteorology independent of the Discourse. In this paper, I will pursue the latter route. My aim is to explain why, and how, Descartes thought that he had deduced ...