Another method by which Aristotle strove to overcome the antithesis between life as a mechanical arrangement and life as a metaphysical conception, was the newly created study of comparative anatomy. The variations in structure and function which accompany variations in the environment, though statically and not dynamically conceived, bring us very near to the truth that biological phenomena are subject to the same general laws of causation as all other phenomena; and it is this truth which, in the science of life, corresponds to the identification of terrestrial with celestial physics in the science of general mechanics. Vitality is not an individualised principle stationed in the heart and serving only to balance opposite forces against one another; but it is diffused through all the tissues, and bestows on them that extraordinary plasticity which responds to the actions of the environment by spontaneous variations capable of being summed up in any direction, and so creating entirely new organic forms without the intervention of any supernatural agency.

V.

We have now to consider how Aristotle treats psychology, not in connexion with biology, but as a distinct science—a separation not quite consistent with his own definition of soul, but forced on him by the traditions of Greek philosophy and by the nature of things. Here the fundamental antithesis assumes a three-fold form. First the theoretical activity of mind is distinguished from its practical activity; the one being exercised on things which cannot, the other on things which can, be changed. Again, a similar distinction prevails within the special province of each. Where truth is the object, knowledge stands opposed to sense; where good is sought, reason rises superior to passion. The one antithesis had been introduced into philosophy by the early physicists, the other by Socrates. They were confounded in the psychology of Plato, and Aristotle had the merit of separating them once more. Yet even he preserves a certain artificial parallelism between them by using the common name Nous, or reason, to denote the controlling member in each. To make his anthropology still more complex, there is a third antithesis to be taken into account, that between the individual and the community, which also sometimes slides into a partial coincidence with the other two.

Aristotle’s treatise on the soul is mainly devoted to a description of the theoretical faculties—sense, and thought or reason. By sense we become acquainted with the material qualities of things; by thought with their forms or ideas. It has been already mentioned that, according to our philosopher, the organism is a system of contrary forces held in equilibrium by the soul, whose seat he supposes to be in the heart. We now learn that every sensation is a disturbance of this equilibrium. In other words, the sensorium being virtually any and every mode of matter, is raised from possibility to actuality by the presence of some one force, such as heat or cold, in sufficient strength to incline the balance that way. Here we have, quite in Aristotle’s usual style, a description instead of an explanation. The atomic notion of thin films thrown off from the object of sense, and falling on the organs of sight or touch, was but a crude guess; still it has more affinity with the discoveries of a Young or a Helmholtz than scholastic phrases about potentiality and actuality. That sensation implies a disturbance of equilibrium is, indeed, an important truth; only, the equilibrium must be conceived as a balance, not of possible sensations, but of molecular states; that is to say, it must be interpreted according to the atomic theory.

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.

It will be seen that we do not consider the two kinds of Nous to differ from each other as a higher and a lower faculty. This, in our opinion, has been the great mistake of the commentators, of those, at least, who do not identify the active Nous with God, or with some agency emanating from God—a hypothesis utterly inconsistent with Aristotle’s theology. They describe it as a faculty, and as concerned with some higher kind of knowledge than what lies within the reach of the passive Nous.[258] But with Aristotle faculty is always a potentiality and a passive recipient, whereas the creative reason is expressly declared to be an actuality, which, in this connexion, can mean nothing but an individual idea. The difficulty is to understand why the objective forms of things should suddenly be spoken of as existing within the mind, and denominated by a term carrying with it such subjective associations as Nous; a difficulty not diminished by the mysterious comparison with light in its relation to colour, an illustration which, in this instance, has only made the darkness visible. We believe that Aristotle was led to express himself as he did by the following considerations. He began by simply conceiving that, just as the senses were raised from potency to actuality through contact with the corresponding qualities in external objects, so also was the reasoning faculty moulded into particular thoughts through contact with the particular things embodying them; thus, for instance, it was led to conceive the general idea of straightness by actual experience of straight lines. It then, perhaps, occurred to him that one and the same object could not produce two such profoundly different impressions as a sensation and a thought; that mind was opposed to external realities by the attribute of self-consciousness; and that a form inherent in matter could not directly impress itself on an immaterial substance. The idea of a creative Nous was, we think, devised in order to escape from these perplexities. The ideal forms of things are carried into the mind, together with the sensations, and in passing through the imagination, become purified from the matter previously associated with them. Thus they may be conceived as part of the mind—in, though not yet of it—and as acting on its highest faculty, the passive Nous. And, by a kind of anticipation, they are called by the name of what they become completely identified with in cognition. As forms of things they are eternal; as thoughts they are self-conscious; while, in both capacities, they are creative, and their creative activity is an essentially immaterial process. Here we have the old confusion between form and function; the old inability to reconcile the claims of the universal and the particular in knowledge and existence. After all, Aristotle is obliged to extract an actuality from the meeting of two possibilities, instead of from the meeting of an actuality and a possibility. Probably the weakness of his own theory did not escape him, for he never subsequently recurs to it.[259]

Aristotle’s work on reproduction is supposed by many to contain a reference to his distinction between the two Reasons, but we are convinced that this is a mistake. What we are told is that at the very first formation of a new being, the vegetative soul, being an exclusively corporeal function, is precontained in the elements furnished by the female; that the sensitive soul is contributed by the male (being, apparently, engendered in the semen by the vital heat of the parent organism); and, finally, that the rational soul, although entirely immaterial, is also carried in with the semen, into which it has first been introduced from without, but where, or when, or how is not more particularly specified.[260] But even were the genetic theory in question perfectly cleared up, it would still throw no light on the distinction between active and passive reason, as the latter alone can be understood by the rational soul to which it refers. For we are expressly informed—what indeed hardly required to be stated—that the embryonic souls exist not in act but in potency.[261] It seems, therefore, that Mr. Edwin Wallace is doubly mistaken when he quotes a sentence from this passage in justification of his statement, that ‘Aristotle would seem almost to identify’ the creative reason ‘with God as the eternal and omnipresent thinker;’[262] first, because it does not refer to the creative Nous at all; and, secondly, because, if it did, the words would not stand the meaning which he puts upon them.[263]

But if even so little as this remains unproved, what are we to think of the astounding assertion, that ‘Aristotle’s theory of a creative reason, fragmentary as that theory is left, is the answer to all materialistic theories of the universe. To Aristotle, as to a subtle Scottish preacher,[264] “the real pre-supposition of all knowledge, or the thought which is the prius of all things, is not the individual’s consciousness of himself as individual, but a thought or self-consciousness which is beyond all individual selves, which is the unity of all individual selves, and their objects, of all thinkers and all objects of thought.”’[265] How can materialism or anything else be possibly refuted by a theory which is so obscurely set forth that no two interpreters are able to agree in their explanation of it? And even were it stated with perfect clearness and fulness, how can any hypothesis be refuted by a mere dogmatic declaration of Aristotle? Are we back in the Middle Ages that his ipse dixit is to decide questions now raised with far ampler means of discussion than he could possess? As to Principal Caird’s metaphysics, we have no wish to dispute their theoretic accuracy, and can only admire the liberality of a Church in which propositions so utterly destructive of traditional orthodoxy are allowed to be preached. But one thing we are certain of, and that is, that whether or not they are consistent with Christian theism, they are utterly inconsistent with Aristotelian principles. Which is the ‘thought or self-consciousness’ referred to, a possibility or an actuality? If the former, it is not a prius, nor is it the creative reason. If the latter, it cannot transcend all or any individual selves, for, with Aristotle, individuals are the sole reality, and the supreme being of his system is pre-eminently individual; neither can it unify them, for, according to Aristotle, two things which are two in actuality cannot be one in actuality.[266]

We now turn to Sir A. Grant, who, as was mentioned at the beginning of the last chapter, makes Aristotle a supporter of the late Prof. Ferrier. We will state the learned Principal’s view in his own words:—