An adequate idea is an entirely true idea. An inadequate idea is one that is mixed with falsity or is totally false or mistaken. Spinoza says that the affects proceed from inadequate or confused knowledge of things, and that we must use reason to arrive at adequate ideas of things.

In a broad sense, these terms refer to what happens when something undergoes a change. More specifically, Spinoza uses “affection” to refer to human feelings and emotions, which he conceives as changes that happen to us; affections in this sense are the subject of Part 3. Spinoza also uses affection to mean an accidental property of a thing.

An attribute is an essential quality pertaining to something—e.g., God’s essence is infinite and all powerful. As Spinoza explains it, attribute is “what the intellect perceives of a substance, as constituting its essence” (1).