Aristotle is more successful when he proceeds to discuss the imagination. He explains it to be a continuance of the movement originally communicated by the felt object to the organ of sense, kept up in the absence of the object itself;—as near an approach to the truth as could be made in his time. And he is also right in saying that the operations of reason are only made possible by the help of what he calls phantasms—that is, faint reproductions of sensations. In addition to this, he points out the connexion between memory and imagination, and enumerates the laws of association briefly, but with great accuracy. He is, however, altogether unaware of their scope. So far from using them to explain all the mental processes, he does not even see that they account for involuntary reminiscence, and limits them to the voluntary operation by which we recall a missing name or other image to consciousness. So far, Aristotle regards the soul as a function, or energy, or perfection of the body, from which it can no more be separated than vision from the eye. It is otherwise with the part of mind which he calls Nous, or Reason—the faculty which takes cognisance of abstract ideas or the pure forms of things. This corresponds, in the microcosm, to the eternal Nous of the macrocosm, and, like it, is absolutely immaterial, not depending for its activity on the exercise of any bodily organ. There is, however, a general analogy between sensation and thought considered as processes of cognition. Previous to experience, the Nous is no thought in particular, but merely a possibility of thinking, like a smooth wax tablet waiting to be written on. It is determined to some particular idea by contact with the objective forms of things, and in this determination is raised from power to actuality. The law of moderation, however, does not apply to thought. Excessive stimulation is first injurious and then destructive to the organs of sense, but we cannot have too much of an idea; the more intense it is the better are we able to conceive all the ideas that come under it, just because ideation is an incorporeal process. And there seems to be this further distinction between sensation and thought, that the latter is much more completely identified with its object than the former; it is in the very act of imprinting themselves on the Nous that the forms of things become perfectly detached from matter, and so attain their final realisation. It is only in our consciousness that the eternal ideas of transient phenomena become conscious of themselves. Such, we take it, is the true interpretation of Aristotle’s famous distinction between an active and a passive Nous. The one, he tells us, _makes_ whatever the other is _made_. The active Nous is like light raising colours from possibility to actuality. It is eternal, but we have no remembrance of its past existence, because the passive Nous, without which it can think nothing, is perishable.