  Spinoza and Descartes agree about the epistemological separation between Thought and Extension, but not about the ontological one. Descartes calls the distinction between attributes of the same substance, and between a given attribute and its substance a “rational distinction,” (Principles, I, §62, CSM, I, p. 214, AT 30) and so, insofar as Thought and Extension belong to the same substance for Spinoza, they would be, in Descartes’ terminology, rationally  distinct.[8]  Spinoza however, says that they are “really distinct.” How exactly to understand the “reality” of the distinction among the attributes is a crucial interpretative matter and is discussed in Sections 1.8.1–1.8.2.