In his On the Soul, iii 4–5, Aristotle wrote that there is one intellect that becomes all things and another that makes all things, just as light makes colors visible. It is separate, impassible, unmixed, and in essence activity; it alone is immortal and eternal. Those few statements are the basis of the theory of the agent intellect.

Aristotle was studied with intense and sometimes imaginative care by ancient and medieval scholars, and his ideas were developed to the extent of dominating thought about human thinking. Our concept arose in Greek but was developed in Arabic and flowered in medieval Latin; "agent intellect" is the English rendering of the Latin intellectus agens, but behind that lie a number of other terms. Furthermore, English writers have sometimes used active instead of agent.

The field falls into three parts: the Greek commentators on Aristotle, the Arabic philosophers...