Saint Thomas Aquinas

Summa Theologiae

First Part
Question 85

Table of Contents

Catalogue of Titles

Logos Virtual Library


Saint Thomas Aquinas (1225-1274)

Summa Theologiae

Translated by Fathers of the English Dominican Province

First Part

Treatise on Man (Questions 75-102)

Of the Mode and Order of Understanding
(In Eight Articles)

We come now to consider the mode and order of understanding. Under this head there are eight points of inquiry: (1) Whether our intellect understands by abstracting the species from the phantasms? (2) Whether the intelligible species abstracted from the phantasms are what our intellect understands, or that whereby it understands? (3) Whether our intellect naturally first understands the more universal? (4) Whether our intellect can know many things at the same time? (5) Whether our intellect understands by the process of composition and division? (6) Whether the intellect can err? (7) Whether one intellect can understand better than another? (8) Whether our intellect understands the indivisible before the divisible?

Whether Our Intellect Understands Corporeal and Material Things by Abstraction from Phantasms?

We proceed thus to the First Article:—

Objection  1. It would seem that our intellect does not understand corporeal and material things by abstraction from the phantasms. For the intellect is false if it understands an object otherwise than as it really is. Now the forms of material things do not exist as abstracted from the particular things represented by the phantasms. Therefore, if we understand material things by abstraction of the species from the phantasm, there will be error in the intellect.

Obj. 2. Further, material things are those natural things which include matter in their definition. But nothing can be understood apart from that which enters into its definition. Therefore material things cannot be understood apart from matter. Now matter is the principle of individualization. Therefore material things cannot be understood by abstraction of the universal from the particular, which is the process whereby the intelligible species is abstracted from the phantasm.

Obj. 3. Further, the Philosopher says (De Anima iii. 7) that the phantasm is to the intellectual soul what color is to the sight. But seeing is not caused by abstraction of species from color, but by color impressing itself on the sight. Therefore neither does the act of understanding take place by abstraction of something from the phantasm, but by the phantasm impressing itself on the intellect.

Obj. 4. Further, the Philosopher says (De Anima iii. 5) there are two things in the intellectual soul—the passive intellect and the active intellect. But it does not belong to the passive intellect to abstract the intelligible species from the phantasm, but to receive them when abstracted. Neither does it seem to be the function of the active intellect, which is related to the phantasm, as light is to color; since light does not abstract anything from color, but rather streams on to it. Therefore in no way do we understand by abstraction from phantasms.

Obj. 5. Further, the Philosopher (De Anima iii. 7) says that the intellect understands the species in the phantasm; and not, therefore, by abstraction.

On the contrary, The Philosopher says (De Anima iii. 4) that things are intelligible in proportion as they are separate from matter. Therefore material things must needs be understood according as they are abstracted from matter and from material images, namely, phantasms.

I answer that, As stated above (Q. 84, A. 7), the object of knowledge is proportionate to the power of knowledge. Now there are three grades of the cognitive powers. For one cognitive power, namely, the sense, is the act of a corporeal organ. And therefore the object of every sensitive power is a form as existing in corporeal matter. And since such matter is the principle of individuality, therefore every power of the sensitive part can only have knowledge of the individual. There is another grade of cognitive power which is neither the act of a corporeal organ, nor in any way connected with corporeal matter; such is the angelic intellect, the object of whose cognitive power is therefore a form existing apart from matter: for though angels know material things, yet they do not know them save in something immaterial, namely, either in themselves or in God. But the human intellect holds a middle place: for it is not the act of an organ; yet it is a power of the soul which is the form of the body, as is clear from what we have said above (Q. 76, A. 1). And therefore it is proper to it to know a form existing individually in corporeal matter, but not as existing in this individual matter. But to know what is in individual matter, not as existing in such matter, is to abstract the form from individual matter which is represented by the phantasms. Therefore we must needs say that our intellect understands material things by abstracting from the phantasms; and through material things thus considered we acquire some knowledge of immaterial things, just as, on the contrary, angels know material things through the immaterial.

But Plato, considering only the immateriality of the human intellect, and not its being in a way united to the body, held that the objects of the intellect are separate ideas; and that we understand not by abstraction, but by participating things abstract, as stated above (Q. 84, A. 1).

Reply Obj. 1. Abstraction may occur in two ways: First, by way of composition and division; thus we may understand that one thing does not exist in some other, or that it is separate therefrom. Secondly, by way of simple and absolute consideration; thus we understand one thing without considering the other. Thus for the intellect to abstract one from another things which are not really abstract from one another, does, in the first mode of abstraction, imply falsehood. But, in the second mode of abstraction, for the intellect to abstract things which are not really abstract from one another, does not involve falsehood, as clearly appears in the case of the senses. For if we understood or said that color is not in a colored body, or that it is separate from it, there would be error in this opinion or assertion. But if we consider color and its properties, without reference to the apple which is colored; or if we express in word what we thus understand, there is no error in such an opinion or assertion, because an apple is not essential to color, and therefore color can be understood independently of the apple. Likewise, the things which belong to the species of a material thing, such as a stone, or a man, or a horse, can be thought of apart from the individualizing principles which do not belong to the notion of the species. This is what we mean by abstracting the universal from the particular, or the intelligible species from the phantasm; that is, by considering the nature of the species apart from its individual qualities represented by the phantasms. If, therefore, the intellect is said to be false when it understands a thing otherwise than as it is, that is so, if the word otherwise refers to the thing understood; for the intellect is false when it understands a thing otherwise than as it is; and so the intellect would be false if it abstracted the species of a stone from its matter in such a way as to regard the species as not existing in matter, as Plato held. But it is not so, if the word otherwise be taken as referring to the one who understands. For it is quite true that the mode of understanding, in one who understands, is not the same as the mode of a thing in existing: since the thing understood is immaterially in the one who understands, according to the mode of the intellect, and not materially, according to the mode of a material thing.

Reply Obj. 2. Some have thought that the species of a natural thing is a form only, and that matter is not part of the species. If that were so, matter would not enter into the definition of natural things. Therefore it must be said otherwise, that matter is twofold, common, and signate or individual; common, such as flesh and bone; and individual, as this flesh and these bones. The intellect therefore abstracts the species of a natural thing from the individual sensible matter, but not from the common sensible matter; for example, it abstracts the species of man from this flesh and these bones, which do not belong to the species as such, but to the individual (Metaph. vii, Did. vi. 10), and need not be considered in the species: whereas the species of man cannot be abstracted by the intellect from flesh and bones.

Mathematical species, however, can be abstracted by the intellect from sensible matter, not only from individual, but also from common matter; not from common intelligible matter, but only from individual matter. For sensible matter is corporeal matter as subject to sensible qualities, such as being cold or hot, hard or soft, and the like: while intelligible matter is substance as subject to quantity. Now it is manifest that quantity is in substance before other sensible qualities are. Hence quantities, such as number, dimension, and figures, which are the terminations of quantity, can be considered apart from sensible qualities; and this is to abstract them from sensible matter; but they cannot be considered without understanding the substance which is subject to the quantity; for that would be to abstract them from common intelligible matter. Yet they can be considered apart from this or that substance; for that is to abstract them from individual intelligible matter. But some things can be abstracted even from common intelligible matter, such as being, unity, power, act, and the like; all these can exist without matter, as is plain regarding immaterial things. Because Plato failed to consider the twofold kind of abstraction, as above explained (ad 1), he held that all those things which we have stated to be abstracted by the intellect, are abstract in reality.

Reply Obj. 3. Colors, as being in individual corporeal matter, have the same mode of existence as the power of sight: therefore they can impress their own image on the eye. But phantasms, since they are images of individuals, and exist in corporeal organs, have not the same mode of existence as the human intellect, and therefore have not the power of themselves to make an impression on the passive intellect. This is done by the power of the active intellect which by turning towards the phantasm produces in the passive intellect a certain likeness which represents, as to its specific conditions only, the thing reflected in the phantasm. It is thus that the intelligible species is said to be abstracted from the phantasm; not that the identical form which previously was in the phantasm is subsequently in the passive intellect, as a body transferred from one place to another.

Reply Obj. 4. Not only does the active intellect throw light on the phantasm: it does more; by its own power it abstracts the intelligible species from the phantasm. It throws light on the phantasm, because, just as the sensitive part acquires a greater power by its conjunction with the intellectual part, so by the power of the active intellect the phantasms are made more fit for the abstraction therefrom of intelligible intentions. Furthermore, the active intellect abstracts the intelligible species from the phantasm, forasmuch as by the power of the active intellect we are able to disregard the conditions of individuality, and to take into our consideration the specific nature, the image of which informs the passive intellect.

Reply Obj. 5. Our intellect both abstracts the intelligible species from the phantasms, inasmuch as it considers the natures of things in universal, and, nevertheless, understands these natures in the phantasms since it cannot understand even the things of which it abstracts the species, without turning to the phantasms, as we have said above (Q. 84, A. 7).

Whether the Intelligible Species Abstracted from the Phantasm Is Related to Our Intellect As That Which Is Understood?

We proceed thus to the Second Article:—

Objection  1. It would seem that the intelligible species abstracted from the phantasm is related to our intellect as that which is understood. For the understood in act is in the one who understands: since the understood in act is the intellect itself in act. But nothing of what is understood is in the intellect actually understanding, save the abstracted intelligible species. Therefore this species is what is actually understood.

Obj. 2. Further, what is actually understood must be in something; else it would be nothing. But it is not in something outside the soul: for, since what is outside the soul is material, nothing therein can be actually understood. Therefore what is actually understood is in the intellect. Consequently it can be nothing else than the aforesaid intelligible species.

Obj. 3. Further, the Philosopher says (1 Peri Herm. i) that words are signs of the passions in the soul. But words signify the things understood, for we express by word what we understand. Therefore these passions of the soul, viz. the intelligible species, are what is actually understood.

On the contrary, The intelligible species is to the intellect what the sensible image is to the sense. But the sensible image is not what is perceived, but rather that by which sense perceives. Therefore the intelligible species is not what is actually understood, but that by which the intellect understands.

I answer that, Some have asserted that our intellectual faculties know only the impression made on them; as, for example, that sense is cognizant only of the impression made on its own organ. According to this theory, the intellect understands only its own impression, namely, the intelligible species which it has received, so that this species is what is understood.

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.

Whether the More Universal Is First in Our Intellectual Cognition?

We proceed thus to the Third Article:—

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. 2. Further, the composite precedes the simple in relation to us. But universals are the more simple. Therefore they are known secondarily by us.

Obj. 3. Further, the Philosopher says (Physic. 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.

Obj. 4. Further, we know causes and principles by their effects. But universals are principles. Therefore universals are secondarily known by us.

On the contrary, We must proceed from the universal to the singular and individual (Physic. i. ibid.).

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 (Physic. i. ibid.), 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 know 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 (Physic. i. ibid.). 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. Neither is it necessary that, as regards us, knowledge of any cause or principle should be secondary: since at times through sensible causes we become acquainted with unknown effects, and sometimes conversely.

Whether We Can Understand Many Things at the Same Time?

We proceed thus to the Fourth Article:—

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. 3. Further, the intellect understands a whole at the same time, such as a man or a house. But a whole contains many parts. Therefore the intellect understands 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.

On the contrary, It is said (Topic. ii. 10) that understanding is of one thing only, knowledge is of many.

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.

Whether Our Intellect Understands by Composition and Division?

We proceed thus to the Fifth Article:—

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.

On the contrary, Words signify the conceptions of the intellect, as the Philosopher says (Peri Herm. i). But in words we find composition and division, as appears in affirmative and negative propositions. Therefore the intellect acts by composition and division.

I answer that, The human intellect must of necessity understand by composition and division. For since the intellect passes from potentiality to act, it has a likeness to things which are generated, which do not attain to perfection all at once but acquire it by degrees: so likewise the human intellect does not acquire perfect knowledge by the first act of apprehension; but it first apprehends something about its object, such as its quiddity, and this is its first and proper object; and then it understands the properties, accidents, and the various relations of the essence. Thus it necessarily compares one thing with another by composition or division; and from one composition and division it proceeds to another, which is the process of reasoning.

But the angelic and the Divine intellect, like all incorruptible things, have their perfection at once from the beginning. Hence the angelic and the Divine intellect have the entire knowledge of a thing at once and perfectly; and hence also in knowing the quiddity of a thing they know at once whatever we can know by composition, division, and reasoning. Therefore the human intellect knows by composition, division and reasoning. But the Divine intellect and the angelic intellect know, indeed, composition, division, and reasoning, not by the process itself, but by understanding the simple essence.

Reply Obj. 1. Composition and division of the intellect are made by differentiating and comparing. Hence the intellect knows many things by composition and division, as by knowing the difference and comparison of things.

Reply Obj. 2. Although the intellect abstracts from the phantasms, it does not understand actually without turning to the phantasms, as we have said (A. 1; Q. 84, A. 7). And forasmuch as it turns to the phantasms, composition and division of the intellect involve time.

Reply Obj. 3. The likeness of a thing is received into the intellect according to the mode of the intellect, not according to the mode of the thing. Wherefore something on the part of the thing corresponds to the composition and division of the intellect; but it does not exist in the same way in the intellect and in the thing. For the proper object of the human intellect is the quiddity of a material thing, which comes under the action of the senses and the imagination. Now in a material thing there is a twofold composition. First, there is the composition of form with matter; and to this corresponds that composition of the intellect whereby the universal whole is predicated of its part: for the genus is derived from common matter, while the difference that completes the species is derived from the form, and the particular from individual matter. The second comparison is of accident with subject: and to this real composition corresponds that composition of the intellect, whereby accident is predicated of subject, as when we say the man is white. Nevertheless composition of the intellect differs from composition of things; for in the latter the things are diverse, whereas composition of the intellect is a sign of the identity of the components. For the above composition of the intellect does not imply that man and whiteness are identical, but the assertion, the man is white, means that the man is something having whiteness: and the subject, which is a man, is identified with a subject having whiteness. It is the same with the composition of form and matter: for animal signifies that which has a sensitive nature; rational, that which has an intellectual nature; man, that which has both; and Socrates that which has all these things together with individual matter; and according to this kind of identity our intellect predicates the composition of one thing with another.

Whether the Intellect Can Be False?

We proceed thus to the Sixth Article:—

Objection  1. It would seem that the intellect can be false; for the Philosopher says (Metaph. vi, Did. v. 4) that truth and falsehood are in the mind. But the mind and intellect are the same, as is shown above (Q. 79, A. 1). Therefore falsehood may be in the mind.

Obj. 2. Further, opinion and reasoning belong to the intellect. But falsehood exists in both. Therefore falsehood can be in the intellect.

Obj. 3. Further, sin is in the intellectual faculty. But sin involves falsehood: for those err that work evil (Prov. xiv. 22). Therefore falsehood can be in the intellect.

On the contrary, Augustine says (QQ. 83, qu. 32), that everyone who is deceived, does not rightly understand that wherein he is deceived. And the Philosopher says (De Anima iii. 10), that the intellect is always true.

I answer that, The Philosopher (ibid. 6) compares intellect with sense on this point. For sense is not deceived in its proper object, as sight in regard to color; has accidentally through some hindrance occurring to the sensile organ—for example, the taste of a fever-stricken person judges a sweet thing to be bitter, through his tongue being vitiated by ill humors. Sense, however, may be deceived as regards common sensible objects, as size or figure; when, for example, it judges the sun to be only a foot in diameter, whereas in reality it exceeds the earth in size. Much more is sense deceived concerning accidental sensible objects, as when it judges that vinegar is honey by reason of the color being the same. The reason of this is evident; for every faculty, as such, is per se directed to its proper object; and things of this kind are always the same. Hence, as long as the faculty exists, its judgment concerning its own proper object does not fail. Now the proper object of the intellect is the quiddity of a material thing; and hence, properly speaking, the intellect is not at fault concerning this quiddity; whereas it may go astray as regards the surroundings of the thing in its essence or quiddity, in referring one thing to another, as regards composition or division, or also in the process of reasoning. Therefore, also in regard to those propositions, which are understood, the intellect cannot err, as in the case of first principles from which arises infallible truth in the certitude of scientific conclusions.

The intellect, however, may be accidentally deceived in the quiddity of composite things, not by the defect of its organ, for the intellect is a faculty that is independent of an organ; but on the part of the composition affecting the definition, when, for instance, the definition of a thing is false in relation to something else, as the definition of a circle applied to a triangle; or when a definition is false in itself as involving the composition of things incompatible; as, for instance, to describe anything as a rational winged animal. Hence as regards simple objects not subject to composite definitions we cannot be deceived unless, indeed, we understand nothing whatever about them, as is said Metaph. ix. (Did. viii. 10).

Reply Obj. 1. The Philosopher says that falsehood is in the intellect in regard to composition and division. The same answer applies to the second objection concerning opinion and reasoning, and to the third objection, concerning the error of the sinner, who errs in the practical judgment of the appetible object. But in the absolute consideration of the quiddity of a thing, and of those things which are known thereby, the intellect is never deceived. In this sense are to be understood the authorities quoted in proof of the opposite conclusion.

Whether One Person Can Understand One and the Same Thing Better Than Another Can?

We proceed thus to the Seventh Article:—

Objection  1. It would seem that one person cannot understand one and the same thing better than another can. For Augustine says (QQ. 83, qu. 32), Whoever understands a thing otherwise than as it is, does not understand it at all. Hence it is clear that there is a perfect understanding, than which none other is more perfect: and therefore there are not infinite degrees of understanding a thing: nor can one person understand a thing better than another can.

Obj. 2. Further, the intellect is true in its act of understanding. But truth, being a certain equality between thought and thing, is not subject to more or less; for a thing cannot be said to be more or less equal. Therefore a thing cannot be more or less understood.

Obj. 3. Further, the intellect is the most formal of all that is in man. But different forms cause different species. Therefore if one man understands better than another, it would seem that they do not belong to the same species.

On the contrary, Experience shows that some understand more profoundly than do others; as one who carries a conclusion to its first principles and ultimate causes understands it better than the one who reduces it only to its proximate causes.

I answer that, A thing being understood more by one than by another may be taken in two senses. First, so that the word more be taken as determining the act of understanding as regards the thing understood; and thus, one cannot understand the same thing more than another, because to understand it otherwise than as it is, either better or worse, would entail being deceived, and such a one would not understand it, as Augustine argues (QQ. 83, qu. 32). In another sense the word more can be taken as determining the act of understanding on the part of him who understands; and so one may understand the same thing better than someone else, through having a greater power of understanding: just as a man may see a thing better with his bodily sight, whose power is greater, and whose sight is more perfect. The same applies to the intellect in two ways. First, as regards the intellect itself, which is more perfect. For it is plain that the better the disposition of a body, the better the soul allotted to it; which clearly appears in things of different species: and the reason thereof is that act and form are received into matter according to matter’s capacity: thus because some men have bodies of better disposition, their souls have a greater power of understanding, wherefore it is said (De Anima ii. 9), that it is to be observed that those who have soft flesh are of apt mind. Secondly, this occurs in regard to the lower powers of which the intellect has need in its operation: for those in whom the imaginative, cogitative, and memorative powers are of better disposition, are better disposed to understand.

The reply to the first objection is clear from the above; likewise the reply to the second, for the truth of the intellect consists in the intellect understanding a thing as it is.

Reply Obj. 3. The difference of form which is due only to the different disposition of matter, causes not a specific but only a numerical difference: for different individuals have different forms, diversified according to the difference of matter.

Whether the Intellect Understands the Indivisible before the Divisible?

We proceed thus to the Eighth Article:—

Objection  1. It would seem that the intellect understands the indivisible before the divisible. For the Philosopher says (Physic. i. 1) that we understand and know from the knowledge of principles and elements. But principles are indivisible, and elements are of divisible things. Therefore the indivisible is known to us before the divisible.

Obj. 2. Further, the definition of a thing contains what is known previously, for a definition proceeds from the first and more known, as is said Topic. vi. 4. But the indivisible is part of the definition of the divisible; as a point comes into the definition of a line; for as Euclid says, a line is length without breadth, the extremities of which are points; also unity comes into the definition of number, for number is multitude measured by one, as is said Metaph. x. (Did. ix. 6). Therefore our intellect understands the indivisible before the divisible.

Obj. 3. Further, Like is known by like. But the indivisible is more like to the intellect than is the divisible; because the intellect is simple (De Anima iii. 4). Therefore our intellect first knows the indivisible.

On the contrary, It is said (ibid. 6) that the indivisible is expressed as a privation. But privation is known secondarily. Therefore likewise is the indivisible.

I answer that, The object of our intellect in its present state is the quiddity of a material thing, which it abstracts from the phantasms, as above stated (Q. 84, A. 7). And since that which is known first and of itself by our cognitive power is its proper object, we must consider its relationship to that quiddity in order to discover in what order the indivisible is known. Now the indivisible is threefold, as is said De Anima iii. 6. First, the continuous is indivisible, since actually it is undivided, although potentially divisible: and this indivisible is known to us before its division, which is a division into parts: because confused knowledge is prior to distinct knowledge, as we have said above (A. 3). Secondly, the indivisible is so called in relation to species, as man’s reason is something indivisible. This way, also, the indivisible is understood before its division into logical parts, as we have said above (ibid.); and again before the intellect disposes and divides by affirmation and negation. The reason of this is that both these kinds of indivisible are understood by the intellect of itself, as being its proper object. The third kind of indivisible is what is altogether indivisible, as a point and unity, which cannot be divided either actually or potentially. And this indivisible is known secondarily, through the privation of divisibility. Wherefore a point is defined by way of privation as that which has no parts; and in like manner the notion of one is that is indivisible, as stated in Metaph. x. (Did. ix. 1). And the reason of this is that this indivisible has a certain opposition to a corporeal being, the quiddity of which is the primary and proper object of the intellect.

But if our intellect understood by participation of certain separate indivisible (forms), as the Platonists maintained, it would follow that a like indivisible is understood primarily; for according to the Platonists what is first is first participated by things.

Reply Obj. 1. In the acquisition of knowledge, principles and elements are not always (known) first: for sometimes from sensible effects we arrive at the knowledge of principles and intelligible causes. But in perfect knowledge, the knowledge of effects always depends on the knowledge of principles and elements: for as the Philosopher says in the same passage: Then do we consider that we know, when we can resolve principles into their causes.

Reply Obj. 2. A point is not included in the definition of a line in general: for it is manifest that in a line of indefinite length, and in a circular line, there is no point, save potentially. Euclid defines a finite straight line: and therefore he mentions a point in the definition, as the limit in the definition of that which is limited. Unity is the measure of number: wherefore it is included in the definition of a measured number. But it is not included in the definition of the divisible, but rather conversely.

Reply Obj. 3. The likeness through which we understand is the species of the known in the knower; therefore a thing is known first, not on account of its natural likeness to the cognitive power, but on account of the power’s aptitude for the object: otherwise sight would perceive hearing rather than color.

First Part
Question 84

First Part
Question 86