Medieval Philosophy

by Peter S. Adamson

It’s traditional to contrast that illumination theory, which has its roots in Augustine, with the hard-nosed Aristotelian empiricism of Aquinas. But Aquinas agrees with the illumination theory to some extent. He too thinks something further is needed in order to transform the particular images of sensation, imagination, and memory into the universal ideas present in our minds. This something extra is the agent intellect. Again he here takes issue with many of his predecessors, especially thinkers of the Islamic world like Avicenna, who postulated a single agent intellect that activates thinking in the individual minds of particular humans. No, says Aquinas: it is true that some principle is needed to confer actual intelligibility and universality on our representations of things, but that principle is within the human soul (DQS 15 resp, ST 1 Q79 a3). Each of us is created by God with our own agent intellect, a “natural light” that we carry within us and that we can use to illuminate the images of things we have encountered in the world around us.