  Spinoza famously claims that we, human minds, only know two attributes—Thought and Extension. This can be seen as arising from the axioms in Part Two: 2A2: “Man thinks,” 2A4: “We feel a certain body is affected in many ways,” 2A5: “We neither feel nor perceive any singular things, except bodies and modes of thinking,” as well as 2P13: “The object of the idea constituting the human mind is the body, or [sive] a certain mode of extension which actually exists, and nothing else” [italics added] (this is true already in KV, 1/27). In Letter 64 Spinoza tries to explain why we can only perceive these two attributes, and he does so by referring back to 2P13 and claims in the letter: “Therefore, the mind’s power of understanding extends only as far as that which this idea of the body contains within itself, or which follows therefrom. Now this idea of the body involves and expresses no other attributes of God than extension and thought.” Although some have found this line of argumentation unsatisfying (e.g. Bennett, 1984, 78–79) it is worth noting that Spinoza here is relying on axioms.