Aquinas: Different Types of Knowledge


I. Central position of the theory of knowledge.

II. Two irreductible types of knowledge. Knowledge of particular objects and its forms.

III. Abstract and general knowledge.

IV. Several forms of intellectual knowledge. Idea, judgment, reasoning.

V. The wide field of consciousness.

I. Central position of the theory of knowledge.

The Schoolmen of the thirteenth century paid special attention to the functions of knowing and willing. They regarded these as the peculiar and privileged possession of the human race, situated as it is at the boundary where matter and spirit meet. For, the dignity of man results from a certain way of knowing which is peculiar to him, and which is called intelligence. This we must define more closely, in order to understand in what sense scholasticism can be described as an intellectualist system of philosophy.

What is knowing? An object is known when it is present in a certain way in the knowing consciousness. When I see a stone lying in a road, the stone is present in me, but not indeed in the material way in which it is present outside of me in the external world. For it is perfectly clear that “the stone is not in me so far as its own peculiar existence is concerned. In the same way, when I grasp mentally the constituent nature of the molecule of water, and the law which governs its decomposition (H20), the material existence of the molecule does not in any way enter into or form part of me; but there is produced in me a kind of reflection of a non-ego. The privilege of a being which knows consists precisely in this ability of being enriched by something which belongs to something else. “Knowing beings are’ differentiated from non-knowing beings by this characteristic: non-knowing beings have only their own reality, but knowing beings are capable of possessing also the reality of something else. For in the knowing being there is a presence of the thing known produced by this thing.”

In what does this presence or reflection of the object in me consist? The Schoolmen do not pretend to fathom the mystery of knowledge; their explanation is a mere analysis of facts revealed by introspection.

Knowing, they observe, is a particular kind of being, a modification, or a vital action of the knowing subject. “The thing known is present in the knowing subject according to the mode of being of the knowing subject”; it bears its mark. “All knowledge results from a similitude of the thing known in the subject knowing.” These two quotations, which were common sayings, sum up well the views of the thirteenth century psychologists. In consequence, knowledge does not result merely from the thing; but rather, the thing known and the subject knowing cooperate in the production of the phenomenon. This intervention of the knowing subject shows us why scholasticism rejected ‘naive realism,’ which disregards the action of the knowing subject, and considers the object known as projected in our minds like an image in a lifeless and passive mirror. On the other hand, since there is an activity of the thing known upon the knowing subject, our representations of reality will be to some extent faithful and correspond to that reality.

II. Two irreducible types of knowledge. Knowledge of particular objects and its forms.

It is of great importance to note that scholasticism distinguishes between two quite different kinds of knowledge: sense knowledge, and intellectual knowledge. In the case of the first — the perception by sight of an oak tree, for instance — everything that I grasp is particularized or individualized, and intimately bound up with conditions of space and time. What I see is this oak tree, with a trunk of this particular form, with a bark of this degree of roughness, with these particular branches and these leaves, in this particular spot in the forest, and which came from a particular acorn at a particular moment of time. If I touch the tree with my hand, the resistance which I encounter is this resistance, just as the sound which I hear in striking the bark is this sound. Our external senses (sight, hearing, smell, taste, touch) put us in contact either with something which is a proper and peculiar object of one sense and which each sense perceives to the exclusion of all the others (sensibile proprium), for instance, color in the case of sight; or else the common object (sensibile commune) of more than one sense, for instance, shape in the case of sight and touch. But in every case the reality perceived by sense is always endowed with individuality.

The same is true of those sensations which are called internal, and which originate, in the scholastic system of classification, from sense-memory (a), from senseconsciousness (b), from instinct (c), or from imagination (d). These are simply so many labels attached to psychological facts which have been duly observed and noted. A few examples will make this clear.

(a) Sense-memory. When I have ceased to look at the oak tree, there remains in me an after-image, which is said to be ‘ preserved ‘ in memory, since I am able to ‘reproduce’ it. We thus possess in ourselves a storehouse of after-images received through the senses, which can be reproduced either spontaneously, or else at the command of the will. It is clear that these vestiges of past sensations, retained and reproduced in this way, are individualized just as the original sensation. If I picture to myself an oak tree, it will always be a picture of one individual oak tree. In the same way, when we realize that a sense perception, or a conscious act of our physiological life, has a certain duration, or takes place after another activity, this realization, which itself involves sense-memory, is once more individual and singular, and presents us with this particular time [It is quite different from the abstract notion of time in general. That belongs to intellectual knowledge.]. The recognition of past time involves reference to particular psychological events, following each other.

(b) Sense-consciousness. Moreover, when I look at an oak tree, something in me tells me that I see. I am aware that I am seeing. My sense perception is followed by ‘ sense-consciousness,’ and the content of this senseconsciousness is particularized. Again, the complex sense cognition of this oak as an object is the result of the coordination of many sense perceptions coming from different senses: the height of the tree, the roughness of its bark, the hollow sound which its trunk gives when struck. There is reason to attribute to the higher animals and to man a central sense [Called sensus communis, which is quite different from what is called to-day common sense. De potentiis animae, ], which combines the external sense perceptions, compares them, and discriminates between them. But in this case also, the result of these operations is individualized, and if we compare for instance two complex sense perceptions of oak trees, each is itself and not the other.

(c) Instinct. We can apply the same to the way in which we recognize that a certain situation is dangerous for us or otherwise. We possess a discriminating power which estimates certain concrete connections between things. We naturally flee from fire, and a shipwrecked man clutches instinctively at a plank, much in the same way as a lamb looks upon a wolf as dangerous, and a bird considers a particular branch of a tree as a suitable resting-place for its nest. This act of sense knowledge always relates to a particular, concrete situation [In the case of the animals, it is the result of a mere instinct by which they appreciate certain things as harmful, and others as suitable (naturalis aestimatio ad cognoscendum nocivum et conveniens). Man, on the other hand, is guided by his reason “which juxtaposes things in order to compare them” (Summa Theol., Ia, q. 78, art. 4)].

(d) Imagination. Again, the constructive imagination, which takes the materials supplied by sensememory and combines them into all sorts of fantastic images — when I imagine, for instance, oak trees as high as mountains, and monstrosities half lion half man — deals with what is particularized. What modern psychologists might call a composite image is to the Schoolmen simply a particular image, made up of characters derived from other particular images.

III. Abstract and general knowledge.

Introspection shows us that we possess another kind of knowledge with characteristics quite different from those we have found in sense knowledge. Intellectual knowledge, instead of being concrete and particularized, is abstract and general. Let us consider this twofold character.

The act of vision of an oak tree, localized in a particular spot, is spontaneously accompanied by notions such as ‘height,’ ‘cylindrical form,’ ‘local motion,’ ‘color,” vital activity,” cell,” matter,” being.’ These notions are indeed derived from this oak tree, but the aspects of reality which we grasp by them are no longer bound up with this particular individual: they reveal to me the whatness or essence (essentia, quidditas) [Quidditas, quod quid est (ta T! ijv that of Aristotle). 1 Object is taken as content of knowledge, as something before the mind: id quod menti objicitur.], or in what height, local motion, life activity, combustion, etc., consist. We confine our attention to certain elements of the thing under consideration, shutting out all the other elements, and stripping them of all particularizing determinations. Abstraction consists precisely in this function and in nothing else. In what height consists is considered apart from everything else, and this selected aspect of reality is no longer related to this oak tree. So that the term abstraction has its etymological meaning (trahere ab, to select from, to draw from; abstraction is sometimes called praecisio mentalis). I possess a treasure-house of abstract notions which relate to all kinds and classes of reality.

It is precisely because this representative content, or object2 of thought (id quod menti objicitur), is no longer bound up entirely with the sight of any particular oak tree, or of a particular human being, etc., that it is seen upon reflection to be applicable to an indefinite number of beings which move, which are cylindrical in form, which manifest vital activities, which are material in nature, etc. This applicability is indefinite — it is ‘universal’ or general, and extends to possible realities as well as existent ones. Universality, therefore, follows upon abstraction, as Thomas remarks.

An abstract notion of mankind seizes what mankind is, as distinct from the whatness of an elephant or a particle of radium. A universal or general notion of mankind implies that such a reality is represented as being able to belong to an endless multitude of men. An abstract notion is thus not necessarily universal, but it may become so. If we bear this in mind, we shall be able to understand better the scholastic solution of the problem of Universals.

We said above that there is no such thing as a general image. Here we say that there is such a thing as a general idea — in fact, that all ideas are general. There is no contradiction here. But those who are unaccustomed to introspection are often unconscious of the vital distinction between image and idea which underlies our two statements. The average man labels his mental content as ‘ images ‘ and ‘ ideas ‘ indiscriminately. Yet reflection will show that they are quite different, and that the one is general while the other is not. This will be made clear from the example of a geometrical theorem— for instance, that the angles of a triangle are together equal to two right angles. We go on at once to picture a triangle, and we say, “Let ABC be a triangle,” and so on. But this image of a triangle is a particular one, whereas our reasoning applies to any and all triangles, existent or only possible. It is thus obvious that the idea or concept triangle is abstract and general, whereas the image is not. The image is here simply a help to our mental consideration and reflection.

The knowledge of reality by means of abstract and universal notions is quite distinct from the particular, individualized knowledge of the external and internal senses. The Schoolmen emphasize this difference by attributing abstract knowledge to the intelligence (intellectus) or reason (ratio). The prominent place occupied in scholasticism by this doctrine of abstract and general knowledge, which we may describe as ‘Psychological Spiritualism’ or better still as Intellectualism, gives the system a definite place in the brilliant group to which belong Plato, Aristotle, Augustine, Plotinus, and in later times, Descartes, Leibnitz, Kant.

Abstraction is the privilege and the distinctive act of man. It is likewise the central activity of our conscious life. The intellectualism, which results from this theory, has an influence over all the branches of philosophy, and we shall see that the rights of human reason are proclaimed and defended at every stage of thought.

IV. Several forms of intellectual knowledge. Idea, judgment, reasoning.

Just as the sense knowledge of particular things has many forms, so also intellectual or abstract knowledge presents several stages — simple apprehension, judgment, and reasoning. They all are fundamentally abstract knowledge, i. e., an understanding of what something is, apart from the particularizing conditions in which it exists, or is capable of existing, outside the mind. Which are the psychological features of these three forms of thought?

In simple apprehension or concept or idea, the mind considers what a thing is, without affirming or denying anything about it. Example: triangle, square, whole, part.

The act of judgment consists in realizing that the content of two ideas — or two objects present to the mind— are in mutual agreement or disagreement. Example: the triangle is a surface; the triangle is not a sphere.

The abstract character which belongs to all our thoughts explains why the mind must make judgments, i. e., affirm this mutual agreement or disagreement. Why is it that we say, “the sum of the angles of a triangle is equal to two right angles,” “wine is changing into vinegar when exposed to the air”? Why are we not content simply to form the ideas’triangle’,’wine’? The answer lies in the richness of reality [By reality we mean something which is not a mere product of the mind, — as opposed to the unreal or fictitious. The real is either existent, e. g., the sun, or else a possible thing, e. g., a triangle. The object of the idea ‘darkness’ is on the contrary unreal.], and in the weakness of our minds. We are incapable of grasping by one single insight, or by one adequate intuition, all that there is in a real being. Only the penetrating eyes of God can exhaust the intelligibility of things by a single intuition, as Leibnitz says, and read in a blade of grass the network of relations which constitutes the history of the universe. Only God is able

To see a World in a grain of sand,
And a Heaven in a wild flower,
Hold Infinity in the palm of your hand,
And Eternity in an hour.

(William Blake, “Auguries of Innocence,” Works, Oxford Edition, 1914, p. 171.)

Our human mind, on the contrary, has to grasp reality piecemeal, and by partial aspects, or partial abstractions. We hunt and stalk reality, in the expressive language of the Schoolmen (venari), but never completely capture it. We discover in a triangle its properties and relations, we seize the activities, reactions of water. Then, after this mental dissection, we refer back to the thing we are studying — now become the subject of a judgment — each and all of the aspects discovered during our patient investigations. These several aspects correspond to several predicates of our judgments. Thus we say S is P, ” water freezes at 0°C, it is composed of H20, it boils at 100°C, etc.” The mind unites things, after it has decomposed them, it makes a synthesis, and thus presents us with a complex object of knowledge. This explains why the notion which a chemist has of water is much richer in content than that of an ordinary person. Likewise, in a fragment of a Greek statue, the common man only knows superficial realities: marble, hardness, whiteness, etc., whilst the archaeologist places the whole statue in the history of art and as a part of an entire civilization. Judgment, then, which unites or separates (compositio, divisio are the scholastic terms), begins and ends with abstraction. It follows from this that any of the aspects of an object (S) may become the predicate (P) of a judgment — not only those aspects which are qualities or attributes, but also activities displayed, state of existence, a relation, a situation in time or space. For example, the horse (S) is drawing a carriage, is sick, has more endurance than a mule, appeared in prehistoric time, in Northern Europe (P). Each of these aspects, which plays a part in making up the richness of the real object S is referred back to S by the mechanism of judgment through the use of the copula is. The verb is does not indicate an inherence in the subject of any of those aspects, but the mental agreement of the subject and the predicate [ Russell has on this point misunderstood the ‘ traditional’ logic. Our Knowledge of the External World, p. 45 (London, 1914).].

The same remarks apply to the process of reasoning, which is simply the production of a new judgment by means of two others, and whose final aim is to enrich the store of abstract knowledge about the special material (such as plants, human acts, numbers, etc.) upon which a special science turns its attention.

V. The wide field of consciousness.

Just as we become witnesses of our sense perceptions, so also consciousness accompanies the exercise of our ideas, our judgments, our reasonings.

Not only is it the case that each act of thought is spontaneously accompanied by a sort of intuition of what is happening in us, but in addition, by an effort of will, we can turn back to this act of thought and investigate either the operation itself as a modification of the ego (psychological consciousness), or else as a mental content, a representation of something (objective consciousness). This is brought about by a sort of twisting or turning back upon ourselves, which we cannot better describe than as reflection (re-flect: to bend back). When I reflect upon the idea of local displacement, of life, or on any other object of thought, it is this object itself which I encounter in the first place, and which I make the material of my inquiries (objective consciousness). The subjective operation which this inquiry involves, the relation of the object to myself, or the internal mechanism of my operation (subjective consciousness) all call for a further concentration, which is much more complicated and difficult. This agrees with and confirms the Thomistic doctrine that knowledge, whether spontaneous or reflective, puts us in presence of something’ which is not merely my own activity, as idealists maintain.

Man alone possesses this privilege of reflecting, or of bending his consciousness upon itself, for reflection is peculiar to spiritual beings. Animals do not reflect; even the human senses cannot do so, and that is the reason why our senses are incapable of correcting by themselves alone the illusions or errors of which they may be victims. Without reflection, I should have no means of knowing that a stick plunged in the water is really straight, in spite of appearances to the contrary. I should remain forever the dupe of sense appearances, for these continue to exist even while reflection is correcting them (VI, 5).

Consciousness accompanies not only our sense perceptions and thoughts, but also certain functions of our physiological life, our appetites, volitions, and sentiments or affections. Further, not only does it accompany the exercise of our activities, but it attains in a more obscure way the ego, which exists in these activities. “I think, therefore I exist,” is an intuition, which St. Augustine and Thomas Aquinas formulated long before Descartes.

Maurice de Wulf’s The System of Thomas Aquinas has been edited and prepared for easier Internet reading by The Moral Liberal, Editor In Chief, Steve Farrell. Footnotes were eliminated in this addition with their information bracketed in the appropriate spots within the text. The original formatting has been improved as well. The original copyright of Maurice de Wulf’s work is held in the Public Domain.

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