II. THE INTERNAL SENSES
The external senses perceive the proper and common sensibles, and only when they are present. Experience teaches, however, that sense knowledge in some way goes beyond the immediate perception of objects. We can, so to speak, store up our sensations and reproduce them at will. Furthermore, we can compare and relate them with one another, directing them to our practical needs. Such activities compel us to admit the existence of sensory powers that exceed the scope of the external senses. These powers are the internal senses.
As is his custom, St. Thomas presents a priori or deductive grounds for the existence of these senses.25 Two reasons in particular seem to establish the need of them. For one thing, the more perfect animals, as noted in connection with the external Senses, have to move from place to place to secure their wants; they must then be able to represent sensible objects to themselves even when not present. Also, they need some way of knowing what is advantageous to them, and what not; consequently, they require a sensory power by which they can perceive what is useful and what harmful. Clearly, such a power goes beyond the mere external perception of sense objects. It is by means of this power, to use a classical example, that the sheep, seeing the wolf, flees, fearing him not because of his color or appearance, but because it recognizes the wolf as an enemy.
It cannot be denied that the aforesaid reasoning has its merits. Still, there is another way of coming to the matter. We can, and this is perhaps more fundamental, base the existence and distinction of the internal senses on the analysis of the objects known through sense knowledge. This analysis reveals certain "objective reasons" or formalities that cannot be reduccd to those of the external senses. As in all such cases, we must acknowledge as many distinct powers as there are new and specifically distinct objects. In the Aristotelian tradition, four such objects are commonly admitted, to which correspond four internal senses, namely, the common sense, the imagination, the estimative power, and memory.
Aristotle's discussion of the internal senses occurs mostly in De Anima26 and in De Memoria et Reminiscentia. Besides his commentary on the corresponding chapters in Aristotle, St. rIlionias also has a summary of their content in the Summa 27 and in Quaestio Disputata de Anima.28 These discussions, which to the casual reader may here and there seem a trifle forced or factitious, will on closer examination reveal a large store of sound observations as well as fine psychological insight.29
1. The Common Sense
Unfortunately the term "common sense" (Latin: sensus communis) is very ambiguous in the vernacular.30 The student in psychology, therefore, should note very carefully what it means in the present context.
Aristotle ascribes three functions to the common sense. First, in conjunction with the external senses it perceives the common sensibles.31 Secondly, it performs a certain reflective function in regard to the activity of the external senses.32 Thirdly, it can discriminate between and compare the objects known by the several external senses. Of these three functions, St. Thomas considers only the last two.
a) Sensory Consciousness. Each of the external senses has, it appears, a certain awareness of its activity; at least it is vaguely aware of its operation when in operation.33 But this mode of awareness is very limited and imperfect, hardly deserving the name "reflection." Properly speaking it is the common sense that knows the acts of the external senses, and this is what is meant by saying that the common sense "reflects" on these acts.'" Thus, it is through this sense that I not only see a colored object, for example, but also know that I see it; or know that I hear when I am hearing, and so on. In general, therefore, this sense induces and integrates what may be called sensory consciousness, which in man is almost inextricably inwoven with his intellectual consciousness.35
b) The integration of sensations into meaningful units. The common sense not only has a certain awareness of the separate acts of the external senses, but also brings them together, so to speak, for comparison and integration. Such activity lies beyond the power of an external sense, limited as it is to its proper object. When, to take an example, I see a thing, it may not only be colored and extended to the eye, but also sonorous to the car, and, if I touch it, coarse and cold to the hand. How is it that all of these separate and different sensations are experienced as belonging together in the same thing, forming a unified whole in my sensory awareness? The answer is that this is the work of the common sense. Without the integral and integrating perception of the common sense, the sensible object would be meaningless.
Because it has the power to compare and conjoin the separate data of each sense, the common sense must be in closest contact with the external senses. In fact, St. Thomas regards it as a common seat for all the outer senses, so that the apparatus of external sense knowledge in general may be considered as a group of individual faculties whose deepest roots lie in a common ground. Nevertheless, the common sense is a distinct power having its specific operations. Within the order of knowledge as a whole, it is like a relay station whose particular function is to convey to the higher faculties the first data of sense. According to Aristotle all animals necessarily have this one internal sense, whereas only higher animals are endowed with the others.
2. The Imagination
In the psychology of Aristotle the imagination fills a double role. It receives and conserves the sense impressions transmitted to it by the common sense; in this capacity it serves as memory, broadly speaking. Secondly, it reproduces sense impressions in the absence of the exterior object.
Because of this twofold activity which it is acknowledged to have, the imagination cannot be identified with any of the senses studied so far, not even with the common sense, which does not conserve and so cannot reproduce sensory images und impressions. St. Thomas is convinced that the activities of the imagination are altogether separate and distinct, so that a power that is only receptive and not retentive of its data, inch as the outer senses and the common sense, cannot account for them. The imagination is also to be distinguished from the other internal senses: from the estimative power, which, as we shall see, apprehends certain nonsensed species and formalities that lie beyond the grasp of the other senses; and from memory, which always implies a reference to the past, something that is equally foreign to the other senses.
'I'he activity of the imagination. Modern psychology devotes much study to the various activities of the imagination, endeavoring to formulate as accurately as possible the laws relating to such phenomena as the reviviscence, the association, and the transformation of images. Among the ancients and Scholastics we find nothing to compare with these more thoroughly detailed and difficult investigations made possible by the advance in method and technique. For all that, however, our forebears had a deep appreciation of the pivotal role of the imagination in human conduct. For them, the influence of the imagination in regard to the emotions was simply fundamental; they also knew it as the faculty in which our dreams are unfolded; and they understood, perhaps better than many after them, that its spell and allurement were largely responsible for error invading the mind. Be it said, in review, that the discoveries of later psychologists in no way contradict these broad observations. Modern knowledge of the imagination finds easy lodgment within the framework of former ideas. The details are new, the substance the same.
3. The Estimative and the Cogitative Power
The doctrine of the estimative and the cogitative power (Latin: vis aestimativa and vis cogitativa) represents one of the most notable features of the Aristotelian and scholastic theory of sense knowledge. This doctrine, like every other in the Peripatetic tradition, stems from experience. It is a fact of common knowledge that animals seek or flee certain objects, not merely because they are pleasant or unpleasant to a particular sense, but also because they are useful or harmful to the nature of the animal as a whole. A sheep, as St. Thomas likes to repeat, flees the wolf, not because of his color or appearance, but because of his threat to the sheep's very existence. Similarly a bird gathers straws, not only to gratify its senses, but in furtherance of the nest it is building. Such formalities as usefulness and harmfulness, however, manifestly fall beyond the reach of the outer and the other internal senses. Nor, in the animal at least, are they grasped by the intellect, which animals do not have. Consequently, we must fall back on a special sensory power whose proper object is the so-called nonsensed species or intentions, intentiones insensatae, the perception of which gives rise to certain motor and appetitive impulses.
As we have just intimated, the doctrine of the estimative power appears to have been evolved as an explanation for certain animal reactions that would otherwise be unaccountable. But similar reactions are observable in the sense activity of man; hence, there is every reason to affirm the existence of this internal sense in man as well. One can readily see, however, that in man's conscious life this faculty will have a very special role to perform, above all because of its influence in regard to the intellect, which is the higher faculty governing man's conduct. For this reason it has received a special name. Its counterpart in the Augustinian tradition is the lower reason, ratio inferior; but St. Thomas adopts the term we have already mentioned, namely, cogitative power. More precisely, the cogitative power differs from the estimative in that its field of operation is broader, but even more in that by reason of its adjacency to the higher faculties of intellect and will, and in regard to conde, individual objects or images, it can institute a manner of comparison and discourse that borders on the strictly rational discourse of man. Hence also this other name for it, which is 'particular reason," ratio particularis, denoting a certain "reason" or discourse on the level of particular, in contrast to universal, objects.
Because of its closeness to intellect - closeness which, obviously, is not a spatial or temporal affinity - the cogitative power, to repeat, fulfills a most important role in the life of man. In general, its function consists in being a sort of mediating faculty between sense on the one hand, which grasps the material singular, and intellect on the other hand, which is the faculty of the abstracted essence. Thus, it serves to prepare the immediate phantasms for the consideration of the intellect; and it is also instrumental in accommodating the higher commands of reason to the practical realm in the world of sense. If, for example, I intend to write something, it is through the cogitative power that my intellect is in cognitional contact with this individual pen I hold in my hand for the purpose in mind, namely, forming certain characters on white paper that lies before me.
Before leaving the cogitative power we should say a word about instinct, since one can hardly study the former without being reminded of the vast labors expended by the moderns on the latter. There is no doubt that the activity attributed to the cogitative power is in some way connected with the group of sensory activities that modern psychologists call instinct, or instinctive. As understood in the older psychology, however, the estimative or cogitative power corresponds only to the cognitional element of modern instinct, which also includes appetitive and locomotive factors. Considered in the light of the older view, instinct would bear a stronger intellectual or imaginational reference, but it would not on that account exclude the possibility of reflex activity that is absolutely independent of knowledge.
4. Sense Memory
The last of the internal senses, memory, has a limited and precise function. The mere conservation and reproduction of sensory impressions is, as said earlier, the work of the imagination. What the memory does is to store up the nonsensed species or intentions known by the estimative and cogitative powers. Thus it is able to revive these experiences in consciousness through recall of the appropriate species. But this is not all. The really distinctive characteristic of memory as understood by Aristotle is its power to represent past things as past: sub ratione praeteriti. Is it not, in fact, true that we say we remember a thing when we can relate the presently revived awareness of it to its moment in the past? Yesterday, for example, I met someone. Today I have a sensory image of this experience in my consciousness, together with its temporal circumstance; today, then, I remember it.
It is an interesting question, and not at all self-evident, how the revived image of a sensory experience is actually brought into association with a determined moment in time. Certainly, it cannot in the first instance be the intellect that performs this function, because the intellect knows its object in the state of abstraction, thus prescinding from the course of time and motion. For this reason, also, purely intellectual memory does not exist in man. The answer must be sought elsewhere. The clue to the problem lies in the fact that time and motion go together. The immediate perception of movement is a sensory process, and this perception forms the basis for the perception of time. Accordingly, the temporal sequence of sensory experiences of movement is somehow inscribed in memory, and can therefore be reproduced by it. Any such experience has only to be presented anew to memory, either in fact or imagination, and it will be able to determine its temporal relation to other experiences.
In animals the recalling of the past takes place automatically, which is to say instinctively; but in man it may also come about through a studied search of the background of experiences that resembles intellectual inquiry. Therefore, even as man's estimative power is more perfect than the animal's and is called the cogitative power and the particular reason, so, for similar reasons, is man's memory more perfect and is called reminiscence.
Here again, in the study of memory, modem psychology, it may be observed, has added much of real value to the knowledge of former times, particularly in the matter of determining more exactly the conditions governing the revival of past experiences and their temporal sequence, such as the laws of learning, retention, and recall. But nothing has been found to change the basic definition of memory or to recast its proper object, which is the ratio praeteriti, the recognition of things as past, something that already Aristotle, with customary insight, so clearly defined. Speaking more generally, one of the great achievements of his philosophy is its contribution to the psychology of the internal senses, displaying as it does such notable success in discerning and determining the precise object not only of memory but of the other internal senses as well.