Whether we can understand many things at the same time?
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.
Objection 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.
Objection 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.
Objection 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 to Objection 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 to Objection 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 to Objection 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 to Objection 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?
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.
Objection 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.
Objection 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 to Objection 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 to Objection 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 to Objection 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?
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.
Objection 2: Further, opinion and reasoning belong to the intellect. But falsehood exists in both. Therefore falsehood can be in the intellect.
Objection 3: Further, sin is in the intellectual faculty. But sin involves falsehood: for "those err that work evil" ( Prov. 14:22 ). Therefore falsehood can be in the intellect.