Spinoza argues that substances are conceptually, and hence causally, isolated from one another. He infers from this that substances cannot be caused to exist or be prevented from existing by any other substance. But since all existing substances must nonetheless have causes and reasons for their existence, the fact that a substance exists must be explained entirely by the substance itself. That is, all existing substances must be self-caused and hence self-explained.
Samuel Newlands: Spinoza’s Modal Metaphysics | plato.stanford.edu 2018-09-14
Spinoza als Konstruktivist: Die „sich selbst genügende“ Substanz, die keine anderen Substanzen neben sich duldet.