In main substance Ibn Rushd reproduces the psychology of Aristotle as interpreted by al-Farabi and Ibn Sina, but with some important modifications. In man is a passive and an active intellect: the active intellect is roused to action by the operation of the Agent Intellect, and thus becomes an acquired intellect; the individual intellects are many, but the Agent Intellect is but one, though present in each, just as the sun is one, but there are in action as many suns as there are bodies which it illuminates. This is the form of the Aristotelian doctrine as it had been transmitted through Ibn Sina; the Agent Intellect is one, but it is as by emanation present in each, so that the quickening power in each one is part of the universal Agent Intellect. But Ibn Rushd differs from his predecessors in his treatment of the passive intellect, the _`aql hayyulani_, which is the seat of latent and potential faculties upon which the Agent operates. In all the earlier systems this passive intellect was regarded as purely individual and as operated on by the emanation of the universal Agent, but Ibn Rushd regarded the passive intellect also as but a portion of a universal soul and as individual only in so far as temporarily occupying an individual body. Even the passive powers are part of a universal force animating the whole of nature. This is the doctrine of _pampsychism_, which exercised so strong an attraction for many of the mediæval scholastics, and has its adherents at the present day; thus James (_Principles of Psychology_, p. 346) says: “I confess that the moment I become metaphysical and try to define the _more_, I find the notion of some sort of an _anima mundi_ thinking in all of us to be a more promising hypothesis, in spite of all its difficulties, than that of a lot of absolutely individual souls.” Ibn Rushd regards Alexander of Aphrodisias as mistaken in supposing that the passive intellect is a mere disposition; it is in us, but belongs to something outside; it is not engendered, it is incorruptible, and so in a sense resembles the Agent Intellect. This doctrine is the very opposite to what is commonly described as materialism, which represents the mind as merely a form of energy produced by the activity of the neural functions. The activity of brain and nerves, according to Ibn Rushd, are due to the presence of an external force; not only, as Aristotle teaches, at least according to Alexander Aph.’s interpretation, is the highest faculty of the reason due to the operation of the external one Agent Intellect, but the passive intellect on which this agent acts is itself part of a great universal soul, which is the one source of all life and the reservoir to which the soul returns when the transitory experience of what we call life is finished.