QUESTION 85: OF THE MODE AND ORDER OF UNDERSTANDING
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
(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
(6) Whether the intellect can err?
(7) Whether one intellect can understand better than another?
(8) Whether our intellect understands the indivisible before the
Article 1: Whether our intellect understands corporeal and material things by abstraction from phantasms?
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.
Objection 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.
Objection 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.
Objection 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.
Objection 5: Further, the Philosopher (De Anima iii, 7) says that "the
intellect understands the species in the phantasm"; and not, therefore,
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 (Question , Article ), 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 the body, as is
clear from what we have said above (Question , Article ). 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 (Question , Article ).
Reply to Objection 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 to Objection 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 form "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 to Objection 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 to Objection 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 to Objection 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 (Question , Article ).
Article 2: Whether the intelligible species abstracted from the phantasm is related to our intellect as that which is understood?
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.
Objection 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
Objection 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
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
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 [*Question , Article ]. 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 to Objection 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 to Objection 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 to Objection 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.
Article 3: Whether the more universal is first in our intellectual cognition?
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.
Objection 2: Further, the composition precedes the simple in relation to us.
But universals are the more simple. Therefore they are known secondarily
Objection 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.
Objection 4: Further, we know causes and principles by their effects. But
universals are principles. Therefore universals are secondarily known by
On the contrary, "We must proceed from the universal to the singular and
individual" (Phys. i, 1)
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
Reply to Objection 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 to Objection 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 to Objection 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 to Objection 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.
Article 4: 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
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
Article 5: 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
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 (Article ; Question , Article ). 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.
Article 6: 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
(Question , Article ). 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.
On the contrary, Augustine says (Questions. 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
I answer that, The Philosopher (De Anima iii, 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 to Objection 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.
Article 7: Whether one person can understand one and the same thing better than another can?
Objection 1: It would seem that one person cannot understand one and the same
thing better than another can. For Augustine says (Questions. 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."
Objection 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.
Objection 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 (Questions. 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 to Objection 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.
Article 8: Whether the intellect understands the indivisible before the divisible?
Objection 1: It would seem that the intellect understands the indivisible
before the divisible. For the Philosopher says (Phys. 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.
Objection 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.
Objection 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
On the contrary, It is said (De Anima iii, 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 (Question , Article ). 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
(Article ). 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
(De Anima iii, 6); 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 to Objection 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 to Objection 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 to Objection 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.