Hume denied the PSR and that is why he was confident in rejecting monism and in embracing skepticism and in accepting a bifurcation of passions and actions in the mind. Spinoza accepted the PSR and so differed from Hume in all these ways. They agreed, though, in seeing the PSR as the lynchpin of philosophy. Spinoza saw the results that the PSR would generate, and he embraced them; Hume recoiled. But for both of them, there was no middle-ground position of the kind that most philosophers are generally and unthinkingly happy to try to occupy.
Michael Della Rocca, Spinoza, (Routledge: 2008), p. 281.