Summa Theologica, Part I (Prima Pars) From the Complete...

This is, however, manifestly false for two reasons. First, because the things we understand are the objects of science; therefore if what we understand is merely the intelligible species in the soul, it would follow that every science would not be concerned with objects outside the soul, but only with the intelligible species within the soul; thus, according to the teaching of the Platonists all science is about ideas, which they held to be actually understood [*Q. 84, A. 1]]. Secondly, it is untrue, because it would lead to the opinion of the ancients who maintained that "whatever seems, is true" [*Aristotle, Metaph. iii. 5, and that consequently contradictories are true simultaneously. For if the faculty knows its own impression only, it can judge of that only. Now a thing seems according to the impression made on the cognitive faculty. Consequently the cognitive faculty will always judge of its own impression as such; and so every judgment will be true: for instance, if taste perceived only its own impression, when anyone with a healthy taste perceives that honey is sweet, he would judge truly; and if anyone with a corrupt taste perceives that honey is bitter, this would be equally true; for each would judge according to the impression on his taste. Thus every opinion would be equally true; in fact, every sort of apprehension.

Therefore it must be said that the intelligible species is related to the intellect as that by which it understands: which is proved thus. There is a twofold action (Metaph. ix, Did. viii, 8), one which remains in the agent; for instance, to see and to understand; and another which passes into an external object; for instance, to heat and to cut; and each of these actions proceeds in virtue of some form. And as the form from which proceeds an act tending to something external is the likeness of the object of the action, as heat in the heater is a likeness of the thing heated; so the form from which proceeds an action remaining in the agent is the likeness of the object. Hence that by which the sight sees is the likeness of the visible thing; and the likeness of the thing understood, that is, the intelligible species, is the form by which the intellect understands. But since the intellect reflects upon itself, by such reflection it understands both its own act of intelligence, and the species by which it understands. Thus the intelligible species is that which is understood secondarily; but that which is primarily understood is the object, of which the species is the likeness. This also appears from the opinion of the ancient philosophers, who said that "like is known by like." For they said that the soul knows the earth outside itself, by the earth within itself; and so of the rest.

If, therefore, we take the species of the earth instead of the earth, according to Aristotle (De Anima iii, 8), who says "that a stone is not in the soul, but only the likeness of the stone"; it follows that the soul knows external things by means of its intelligible species.

Reply Obj. 1: The thing understood is in the intellect by its own likeness; and it is in this sense that we say that the thing actually understood is the intellect in act, because the likeness of the thing understood is the form of the intellect, as the likeness of a sensible thing is the form of the sense in act. Hence it does not follow that the intelligible species abstracted is what is actually understood; but rather that it is the likeness thereof.

Reply Obj. 2: In these words "the thing actually understood" there is a double implication—the thing which is understood, and the fact that it is understood. In like manner the words "abstract universal" imply two things, the nature of a thing and its abstraction or universality. Therefore the nature itself to which it occurs to be understood, abstracted or considered as universal is only in individuals; but that it is understood, abstracted or considered as universal is in the intellect. We see something similar to this is in the senses. For the sight sees the color of the apple apart from its smell. If therefore it be asked where is the color which is seen apart from the smell, it is quite clear that the color which is seen is only in the apple: but that it be perceived apart from the smell, this is owing to the sight, forasmuch as the faculty of sight receives the likeness of color and not of smell. In like manner humanity understood is only in this or that man; but that humanity be apprehended without conditions of individuality, that is, that it be abstracted and consequently considered as universal, occurs to humanity inasmuch as it is brought under the consideration of the intellect, in which there is a likeness of the specific nature, but not of the principles of individuality.

Reply Obj. 3: There are two operations in the sensitive part. One, in regard of impression only, and thus the operation of the senses takes place by the senses being impressed by the sensible. The other is formation, inasmuch as the imagination forms for itself an image of an absent thing, or even of something never seen. Both of these operations are found in the intellect. For in the first place there is the passion of the passive intellect as informed by the intelligible species; and then the passive intellect thus informed forms a definition, or a division, or a composition, expressed by a word. Wherefore the concept conveyed by a word is its definition; and a proposition conveys the intellect's division or composition. Words do not therefore signify the intelligible species themselves; but that which the intellect forms for itself for the purpose of judging of external things. _______________________

Objection 1: It would seem that the more universal is not first in our intellectual cognition. For what is first and more known in its own nature, is secondarily and less known in relation to ourselves. But universals come first as regards their nature, because "that is first which does not involve the existence of its correlative" (Categor. ix). Therefore the universals are secondarily known as regards our intellect.

Obj. 3: Further, the Philosopher says (Phys. i, 1), that the object defined comes in our knowledge before the parts of its definition. But the more universal is part of the definition of the less universal, as "animal" is part of the definition of "man." Therefore the universals are secondarily known by us.

I answer that, In our knowledge there are two things to be considered. First, that intellectual knowledge in some degree arises from sensible knowledge: and, because sense has singular and individual things for its object, and intellect has the universal for its object, it follows that our knowledge of the former comes before our knowledge of the latter. Secondly, we must consider that our intellect proceeds from a state of potentiality to a state of actuality; and every power thus proceeding from potentiality to actuality comes first to an incomplete act, which is the medium between potentiality and actuality, before accomplishing the perfect act. The perfect act of the intellect is complete knowledge, when the object is distinctly and determinately known; whereas the incomplete act is imperfect knowledge, when the object is known indistinctly, and as it were confusedly. A thing thus imperfectly known, is known partly in act and partly in potentiality, and hence the Philosopher says (Phys. i, 1), that "what is manifest and certain is known to us at first confusedly; afterwards we know it by distinguishing its principles and elements." Now it is evident that to know an object that comprises many things, without proper knowledge of each thing contained in it, is to know that thing confusedly. In this way we can have knowledge not only of the universal whole, which contains parts potentially, but also of the integral whole; for each whole can be known confusedly, without its parts being known.

But to know distinctly what is contained in the universal whole is to know the less common, as to "animal" indistinctly is to know it as "animal"; whereas to know "animal" distinctly is know it as "rational" or "irrational animal," that is, to know a man or a lion: therefore our intellect knows "animal" before it knows man; and the same reason holds in comparing any more universal idea with the less universal.

Moreover, as sense, like the intellect, proceeds from potentiality to act, the same order of knowledge appears in the senses. For by sense we judge of the more common before the less common, in reference both to place and time; in reference to place, when a thing is seen afar off it is seen to be a body before it is seen to be an animal; and to be an animal before it is seen to be a man, and to be a man before it seen to be Socrates or Plato; and the same is true as regards time, for a child can distinguish man from not man before he distinguishes this man from that, and therefore "children at first call men fathers, and later on distinguish each one from the others" (Phys. i, 1). The reason of this is clear: because he who knows a thing indistinctly is in a state of potentiality as regards its principle of distinction; as he who knows genus is in a state of potentiality as regards "difference." Thus it is evident that indistinct knowledge is midway between potentiality and act.

We must therefore conclude that knowledge of the singular and individual is prior, as regards us, to the knowledge of the universal; as sensible knowledge is prior to intellectual knowledge. But in both sense and intellect the knowledge of the more common precedes the knowledge of the less common.

Reply Obj. 1: The universal can be considered in two ways. First, the universal nature may be considered together with the intention of universality. And since the intention of universality—viz. the relation of one and the same to many—is due to intellectual abstraction, the universal thus considered is a secondary consideration. Hence it is said (De Anima i, 1) that the "universal animal is either nothing or something secondary." But according to Plato, who held that universals are subsistent, the universal considered thus would be prior to the particular, for the latter, according to him, are mere participations of the subsistent universals which he called ideas.

Secondly, the universal can be considered in the nature itself—for instance, animality or humanity as existing in the individual. And thus we must distinguish two orders of nature: one, by way of generation and time; and thus the imperfect and the potential come first. In this way the more common comes first in the order of nature; as appears clearly in the generation of man and animal; for "the animal is generated before man," as the Philosopher says (De Gener. Animal ii, 3). The other order is the order of perfection or of the intention of nature: for instance, act considered absolutely is naturally prior to potentiality, and the perfect to the imperfect: thus the less common comes naturally before the more common; as man comes before animal. For the intention of nature does not stop at the generation of animal but goes on to the generation of man.

Reply Obj. 2: The more common universal may be compared to the less common, as the whole, and as the part. As the whole, considering that in the more universal is potentially contained not only the less universal, but also other things, as in "animal" is contained not only "man" but also "horse." As part, considering that the less common contains in its idea not only the more common, but also more; as "man" contains not only "animal" but also "rational." Therefore "animal" in itself comes into our knowledge before "man"; but "man" comes before "animal" considered as part of the same idea.

Reply Obj. 3: A part can be known in two ways. First, absolutely considered in itself; and thus nothing prevents the parts being known before the whole, as stones are known before a house is known. Secondly as belonging to a certain whole; and thus we must needs know the whole before its parts. For we know a house vaguely before we know its different parts. So likewise principles of definition are known before the thing defined is known; otherwise the thing defined would not be known at all. But as parts of the definition they are known after. For we know man vaguely as man before we know how to distinguish all that belongs to human nature.

Reply Obj. 4: The universal, as understood with the intention of universality, is, indeed, in a way, a principle of knowledge, in so far as the intention of universality results from the mode of understanding by way of abstraction. But what is a principle of knowledge is not of necessity a principle of existence, as Plato thought: since at times we know a cause through its effect, and substance through accidents. Wherefore the universal thus considered, according to the opinion of Aristotle, is neither a principle of existence, nor a substance, as he makes clear (Metaph. vii, Did. vi, 13). But if we consider the generic or specific nature itself as existing in the singular, thus in a way it is in the nature of a formal principle in regard to the singulars: for the singular is the result of matter, while the idea of species is from the form. But the generic nature is compared to the specific nature rather after the fashion of a material principle, because the generic nature is taken from that which is material in a thing, while the idea of species is taken from that which is formal: thus the notion of animal is taken from the sensitive part, whereas the notion of man is taken from the intellectual part. Thus it is that the ultimate intention of nature is to the species and not to the individual, or the genus: because the form is the end of generation, while matter is for the sake of the form.

Objection 1: It would seem that we can understand many things at the same time. For intellect is above time, whereas the succession of before and after belongs to time. Therefore the intellect does not understand different things in succession, but at the same time.

Obj. 2: Further, there is nothing to prevent different forms not opposed to each other from actually being in the same subject, as, for instance, color and smell are in the apple. But intelligible species are not opposed to each other. Therefore there is nothing to prevent the same intellect being in act as regards different intelligible species, and thus it can understand many things at the same time.

Obj. 4: Further, we cannot know the difference between two things unless we know both at the same time (De Anima iii, 2), and the same is to be said of any other comparison. But our intellect knows the difference and comparison between one thing and another. Therefore it knows many things at the same time.

I answer that, The intellect can, indeed, understand many things as one, but not as many: that is to say by one but not by many intelligible species. For the mode of every action follows the form which is the principle of that action. Therefore whatever things the intellect can understand under one species, it can understand at the same time: hence it is that God sees all things at the same time, because He sees all in one, that is, in His Essence. But whatever things the intellect understands under different species, it does not understand at the same time. The reason of this is that it is impossible for one and the same subject to be perfected at the same time by many forms of one genus and diverse species, just as it is impossible for one and the same body at the same time to have different colors or different shapes. Now all intelligible species belong to one genus, because they are the perfections of one intellectual faculty: although the things which the species represent belong to different genera. Therefore it is impossible for one and the same intellect to be perfected at the same time by different intelligible species so as actually to understand different things.

Reply Obj. 1: The intellect is above that time, which is the measure of the movement of corporeal things. But the multitude itself of intelligible species causes a certain vicissitude of intelligible operations, according as one operation succeeds another. And this vicissitude is called time by Augustine, who says (Gen. ad lit. viii, 20, 22), that "God moves the spiritual creature through time."

Reply Obj. 2: Not only is it impossible for opposite forms to exist at the same time in the same subject, but neither can any forms belonging to the same genus, although they be not opposed to one another, as is clear from the examples of colors and shapes.

Reply Obj. 3: Parts can be understood in two ways. First, in a confused way, as existing in the whole, and thus they are known through the one form of the whole, and so are known together. In another way they are known distinctly: thus each is known by its species; and so they are not understood at the same time.

Reply Obj. 4: If the intellect sees the difference or comparison between one thing and another, it knows both in relation to their difference or comparison; just, as we have said above (ad 3), as it knows the parts in the whole. _______________________

Objection 1: It would seem that our intellect does not understand by composition and division. For composition and division are only of many; whereas the intellect cannot understand many things at the same time. Therefore it cannot understand by composition and division.

Obj. 2: Further, every composition and division implies past, present, or future time. But the intellect abstracts from time, as also from other individual conditions. Therefore the intellect does not understand by composition and division.

Obj. 3: Further, the intellect understands things by a process of assimilation to them. But composition and division are not in things, for nothing is in things but what is signified by the predicate and the subject, and which is one and the same, provided that the composition be true, for "man" is truly what "animal" is. Therefore the intellect does not act by composition and division.