  Immediately after wrapping up his proof for substance monism in Ip14, Spinoza claims in the next proposition that “Whatever is, is in God, and nothing can be or be conceived without God” (Ip15). By the definition of a mode in Id5, Ip15 implies that everything that exists other than God is a mode or affection of God. To understand the import of this claim, it is important to understand what a mode is and what is it for a mode to be in a substance, for Spinoza.