Spinoza is a metaphysician. I emphasize this fact here (and in my title) because one can discover what is most exciting and important about Spinoza's psychology only by seeing it as emerging from his metaphysics. Spinoza is a systematic philosopher and nowhere is his system more ambitious and under more strain than in his attempt to derive an account of human motivation, affects, and other mental states from his general metaphysics.

This project of deriving psychology from metaphysics stems from Spinoza’s guiding belief in naturalism about human beings - a belief he famously expresses as the view that man in nature is not a kingdom within a kingdom (E 3pr). For Spinoza, the principles at work throughout nature in general also govern human psychology. The clearest statement of his view occurs in the Preface to Part 3 of the Ethics: