In the Ethics, Spinoza speaks of “adequate idea” (idea adequata) and “adequate cause” (causa adequata). Spinoza defines these as follows:

For Spinoza adequate ideas are equivalent to true ideas (E2def4) and to see the connection between adequate causation and adequate ideas we will consider true ideas. A true idea is an idea that agrees with its object (E1a6) and it is also self-presenting in the sense that no one can have a true idea without knowing that it is true (E2p43s) A true idea not only tells how things are or how a thing should be correctly defined but also shows its own truth to the subject who has the idea. The following example, in which Spinoza gives a definition of a sphere, explains this