  The second major stage of Spinoza’s argument is to prove that God is the only possible substance. I will not here rehearse all the details of Spinoza’s argument to this conclusion (for two recent discussions, see Lin 2007 and Della Rocca 2001). Like his argument for (1), Spinoza’s argument for (2) relies on the PSR. Here is one possible sketch of Spinoza’s overall argument for (2):