Averroes expounds his thoughts on psychology in his three commentaries on Aristotle's On the Soul. Averroes is interested in explaining the human intellect using philosophical methods and by interpreting Aristotle's ideas. His position on the topic changed throughout his career as his thoughts developed. In his short commentary, the first of the three works, Averroes follows Ibn Bajja 's theory that something called the " material intellect " stores specific images that a person encounters. These images serve as basis for the "unification" by the universal " agent intellect ", which, once it happens, allow a person to gain universal knowledge about that concept. In his middle commentary, Averroes moves towards the ideas of Al-Farabi and Avicenna, saying the agent intellect gives humans the power of universal understanding, which is the material intellect. Once the person has sufficient empirical encounters with a certain concept, the power activates and gives the person universal knowledge (see also logical induction).