According to spinoza, for every material body that exists (every mode of extension) there is an idea that represents it. This view follows from the proof for iip3 (p. 150), where spinoza argues that there is an idea of everything that exists: so there is an idea of every mode of every attribute, including every mode of extension. Moreover the order and connection among ideas parallels the order and connection among things (iip7; p. 151). However, while the modes of each attribute run parallel to one another they are causally isolated from each other. Spinoza claims that the human mind is the idea of a particular finite material body (iip13; p. Of course, the mind is not a single idea, but a collection of ideas. Specifically, the mind is composed of all the different ideas representing all the different parts of the body (iip15; p. 157).
