In man five outer powers exist, which are the agents of perception, that is to say, through these five powers man perceives material beings. These are sight, which perceives visible forms; hearing, which perceives audible sounds; smell which perceives odours; taste, which perceives foods; and feeling, which is in all parts of the body, and perceives tangible things. These five powers perceive outward existences. Man has also spiritual powers: imagination, which conceives things; thought, which reflects upon realities; comprehension, which comprehends realities; memory, which retains whatever man imagines, thinks, and comprehends . . . For instance, sight is one of the outer powers; it sees and perceives this flower, and conveys this perception to the inner power -- the common faculty -- which transmits this perception to the power of imagination, which in its turn conceives and forms this image and transmits it to the power of thought; the power of thought reflects, and having grasped the reality, conveys it to the power of comprehension; the comprehension, when it has comprehended it, delivers the image of the object perceived to the memory, and the memory keeps it in its repository.