Within human consciousness there are lower and higher grades, and Aristotle has taken great pains to trace these from the bottom to the top. These stages of consciousness are what are ordinarily called "faculties." But Aristotle notes that it is nonsense to talk, as Plato did, of the "parts" of the soul. The soul, being a single indivisible being, has no parts. They are different aspects of the activity of one and the same being; different stages of its development. They can no more be separated than the convex and concave aspects of a curve. The lowest faculty, if we must use that word, is sense-perception. Now what we perceive in a thing is its qualities. Perception tells us that a piece of gold is {299} heavy, yellow, etc. The underlying substratum which supports the qualities cannot be perceived. This means that the matter is unknowable, the form knowable, for the qualities are part of the form. Sense-perception, therefore, takes place when the object stamps its form upon the soul. This is important for what it implies rather than what it states. It shows the thoroughly idealistic trend of Aristotle's thought. For if the form is what is knowable in a thing, the more form there is, the more knowable it will be. Absolute form, God, will be the absolutely knowable. That the Absolute is what alone is completely knowable, intelligible, and comprehensible, and the finite and material comparatively unknowable, is a point of view essential to idealism, and stands in marked contrast to the popular idea of rationalism that the Absolute is unknowable, and matter knowable. For idealism, the Absolute is reason, thought. What can be more thoroughly intelligible than reason? What can thought understand, if not thought? This, of course, is not stated by Aristotle. But it is implied in his theory of sense-perception. Next in the scale above the senses comes the common sense. This has nothing to do with what we understand by that phrase in every-day language. It means the central sensation-ganglion in which isolated sensations meet, are combined, and form a unity of experience. We saw, in considering Plato, that the simplest kind of knowledge, such as, "this paper is white," involves, not only isolated sensations, but their comparison and contrast. Bare sensations would not even make objects. For every object is a combined bundle of sensations. What thus combines the various sensations, and in {300} particular those received from different sense-organs, what compares and contrasts them, and turns them from a blind medley of phantasms into a definite experience, a single cosmos, is the common sense. Its organ is the heart. Above the common sense is the faculty of imagination. By this Aristotle means, not the creative imagination of the artist, but the power, which everyone possesses, of forming mental images and pictures. This is due to the excitation in the sense-organ continuing after the object has ceased to affect it.