• First (pp. 87f), Descartes discusses our knowledge of mathematics. Notice how he presents this as our clear and distinct ideas of external things: all that we know with certainty of material things are their mathematical properties.

• Next (pp. 88-91), and by analogy with his discussion of mathematics, he provides a second proof of the existence of God. This is a version of a well-known proof, usually referred to as the “ontological argument.” This sort of argument was first presented by Anselm of Canterbury (1033-1109). It was rejected by Thomas Aquinas (1225-1274), whose views were central to the development of scholasticism, and you can think of Descartes as reviving an idea that had been neglected for centuries.

• Finally (pp. 91f), Descartes returns to the issue of the relation between the existence of God and his principle that clear and distinct ideas are grounds for certain knowledge. This rounds off the discussion, begun in meditation 2, of his knowledge of himself and its consequences, and it prepares for his discussion in the final meditation of his knowledge of external things other than God. Notice also that, while he has now dismissed the possibility of an evil demon, he has not yet dismissed doubts based on the possibility that he is dreaming.