QUESTION 87: HOW THE INTELLECTUAL SOUL KNOWS ITSELF AND ALL WITHIN ITSELF
We have now to consider how the intellectual soul knows itself and all
within itself. Under this head there are four points of inquiry:
(1) Whether the soul knows itself by its own essence?
(2) Whether it knows its own habits?
(3) How does the intellect know its own act?
(4) How does it know the act of the will?
Article 1: Whether the intellectual soul knows itself by its essence?
Objection 1: It would seem that the intellectual soul knows itself by its own
essence. For Augustine says (De Trin. ix, 3), that "the mind knows
itself, because it is incorporeal."
Objection 2: Further, both angels and human souls belong to the genus of
intellectual substance. But an angel understands itself by its own
essence. Therefore likewise does the human soul.
Objection 3: Further, "in things void of matter, the intellect and that which
is understood are the same" (De Anima iii, 4). But the human mind is void
of matter, not being the act of a body as stated above (Question , Article ).
Therefore the intellect and its object are the same in the human mind;
and therefore the human mind understands itself by its own essence.
On the contrary, It is said (De Anima iii, 4) that "the intellect
understands itself in the same way as it understands other things." But
it understands other things, not by their essence, but by their
similitudes. Therefore it does not understand itself by its own essence.
I answer that, Everything is knowable so far as it is in act, and not,
so far as it is in potentiality (Metaph. ix, Did. viii, 9): for a thing
is a being, and is true, and therefore knowable, according as it is
actual. This is quite clear as regards sensible things, for the eye does
not see what is potentially, but what is actually colored. In like manner
it is clear that the intellect, so far as it knows material things, does
not know save what is in act: and hence it does not know primary matter
except as proportionate to form, as is stated Phys. i, 7. Consequently
immaterial substances are intelligible by their own essence according as
each one is actual by its own essence.
Therefore it is that the Essence of God, the pure and perfect act, is
simply and perfectly in itself intelligible; and hence God by His own
Essence knows Himself, and all other things also. The angelic essence
belongs, indeed, to the genus of intelligible things as "act," but not as
a "pure act," nor as a "complete act," and hence the angel's act of
intelligence is not completed by his essence. For although an angel
understands himself by his own essence, still he cannot understand all
other things by his own essence; for he knows things other than himself
by their likenesses. Now the human intellect is only a potentiality in
the genus of intelligible beings, just as primary matter is a
potentiality as regards sensible beings; and hence it is called
"possible" [*Possibilis---elsewhere in this translation rendered
"passive"---Ed.]. Therefore in its essence the human mind is potentially
understanding. Hence it has in itself the power to understand, but not
to be understood, except as it is made actual. For even the Platonists
asserted than an order of intelligible beings existed above the order of
intellects, forasmuch as the intellect understands only by participation
of the intelligible; for they said that the participator is below what it
participates. If, therefore, the human intellect, as the Platonists held,
became actual by participating separate intelligible forms, it would
understand itself by such participation of incorporeal beings. But as in
this life our intellect has material and sensible things for its proper
natural object, as stated above (Question , Article ), it understands itself
according as it is made actual by the species abstracted from sensible
things, through the light of the active intellect, which not only
actuates the intelligible things themselves, but also, by their
instrumentality, actuates the passive intellect. Therefore the intellect
knows itself not by its essence, but by its act. This happens in two
ways: In the first place, singularly, as when Socrates or Plato perceives
that he has an intellectual soul because he perceives that he
understands. In the second place, universally, as when we consider the
nature of the human mind from knowledge of the intellectual act. It is
true, however, that the judgment and force of this knowledge, whereby we
know the nature of the soul, comes to us according to the derivation of
our intellectual light from the Divine Truth which contains the types of
all things as above stated (Question , Article ). Hence Augustine says (De Trin.
ix, 6): "We gaze on the inviolable truth whence we can as perfectly as
possible define, not what each man's mind is, but what it ought to be in
the light of the eternal types." There is, however, a difference between
these two kinds of knowledge, and it consists in this, that the mere
presence of the mind suffices for the first; the mind itself being the
principle of action whereby it perceives itself, and hence it is said to
know itself by its own presence. But as regards the second kind of
knowledge, the mere presence of the mind does not suffice, and there is
further required a careful and subtle inquiry. Hence many are ignorant of
the soul's nature, and many have erred about it. So Augustine says (De
Trin. x, 9), concerning such mental inquiry: "Let the mind strive not to
see itself as if it were absent, but to discern itself as present"---i.e.
to know how it differs from other things; which is to know its essence
Reply to Objection 1: The mind knows itself by means of itself, because at length
it acquires knowledge of itself, though led thereto by its own act:
because it is itself that it knows since it loves itself, as he says in
the same passage. For a thing can be called self-evident in two ways,
either because we can know it by nothing else except itself, as first
principles are called self-evident; or because it is not accidentally
knowable, as color is visible of itself, whereas substance is visible by
Reply to Objection 2: The essence of an angel is an act in the genus of
intelligible things, and therefore it is both intellect and the thing
understood. Hence an angel apprehends his own essence through itself: not
so the human mind, which is either altogether in potentiality to
intelligible things---as is the passive intellect---or is the act of
intelligible things abstracted from the phantasms---as is the active
Reply to Objection 3: This saying of the Philosopher is universally true in every
kind of intellect. For as sense in act is the sensible in act, by reason
of the sensible likeness which is the form of sense in act, so likewise
the intellect in act is the object understood in act, by reason of the
likeness of the thing understood, which is the form of the intellect in
act. So the human intellect, which becomes actual by the species of the
object understood, is itself understood by the same species as by its own
form. Now to say that in "things without matter the intellect and what is
understood are the same," is equal to saying that "as regards things
actually understood the intellect and what is understood are the same."
For a thing is actually understood in that it is immaterial. But a
distinction must be drawn: since the essences of some things are
immaterial---as the separate substances called angels, each of which is
understood and understands, whereas there are other things whose essences
are not wholly immaterial, but only the abstract likenesses thereof.
Hence the Commentator says (De Anima iii) that the proposition quoted is
true only of separate substances; because in a sense it is verified in
their regard, and not in regard of other substances, as already stated
(Reply OBJ 2).
Article 2: Whether our intellect knows the habits of the soul by their essence?
Objection 1: It would seem that our intellect knows the habits of the soul by
their essence. For Augustine says (De Trin. xiii, 1): "Faith is not seen
in the heart wherein it abides, as the soul of a man may be seen by
another from the movement of the body; but we know most certainly that it
is there, and conscience proclaims its existence"; and the same principle
applies to the other habits of the soul. Therefore the habits of the soul
are not known by their acts, but by themselves.
Objection 2: Further, material things outside the soul are known by their
likeness being present in the soul, and are said therefore to be known by
their likenesses. But the soul's habits are present by their essence in
the soul. Therefore the habits of the soul are known by their essence.
Objection 3: Further, "whatever is the cause of a thing being such is still
more so." But habits and intelligible species cause things to be known by
the soul. Therefore they are still more known by the soul in themselves.
On the contrary, Habits like powers are the principles of acts. But as is said (De Anima ii, 4), "acts and operations are logically prior to powers." Therefore in the same way they are prior to habits; and thus habits, like the powers, are known by their acts.
I answer that, A habit is a kind of medium between mere power and mere
act. Now, it has been said (Article ) that nothing is known but as it is
actual: therefore so far as a habit fails in being a perfect act, it
falls short in being of itself knowable, and can be known only by its
act; thus, for example, anyone knows he has a habit from the fact that he
can produce the act proper to that habit; or he may inquire into the
nature and idea of the habit by considering the act. The first kind of
knowledge of the habit arises from its being present, for the very fact
of its presence causes the act whereby it is known. The second kind of
knowledge of the habit arises from a careful inquiry, as is explained
above of the mind (Article ).
Reply to Objection 1: Although faith is not known by external movement of the
body, it is perceived by the subject wherein it resides, by the interior
act of the heart. For no one knows that he has faith unless he knows that
Reply to Objection 2: Habits are present in our intellect, not as its object
since, in the present state of life, our intellect's object is the nature
of a material thing as stated above (Question , Article ), but as that by which
Reply to Objection 3: The axiom, "whatever is the cause of a thing being such, is
still more so," is true of things that are of the same order, for
instance, of the same kind of cause; for example, we may say that health
is desirable on account of life, and therefore life is more desirable
still. But if we take things of different orders the axiom is not true:
for we may say that health is caused by medicine, but it does not follow
that medicine is more desirable than health, for health belongs to the
order of final causes, whereas medicine belongs to the order of efficient
causes. So of two things belonging essentially to the order of the
objects of knowledge, the one which is the cause of the other being
known, is the more known, as principles are more known than conclusions.
But habit as such does not belong to the order of objects of knowledge;
nor are things known on account of the habit, as on account of an object
known, but as on account of a disposition or form whereby the subject
knows: and therefore the argument does not prove.
Article 3: Whether our intellect knows its own act?
Objection 1: It would seem that our intellect does not know its own act. For
what is known is the object of the knowing faculty. But the act differs
from the object. Therefore the intellect does not know its own act.
Objection 2: Further, whatever is known is known by some act. If, then, the intellect knows its own act, it knows it by some act, and again it knows that act by some other act; this is to proceed indefinitely, which seems impossible.
Objection 3: Further, the intellect has the same relation to its act as sense
has to its act. But the proper sense does not feel its own act, for this
belongs to the common sense, as stated De Anima iii, 2. Therefore neither
does the intellect understand its own act.
On the contrary, Augustine says (De Trin. x, 11), "I understand that I
I answer that, As stated above (Articles ,2) a thing is intelligible
according as it is in act. Now the ultimate perfection of the intellect
consists in its own operation: for this is not an act tending to
something else in which lies the perfection of the work accomplished, as
building is the perfection of the thing built; but it remains in the
agent as its perfection and act, as is said Metaph. ix, Did. viii, 8.
Therefore the first thing understood of the intellect is its own act of
understanding. This occurs in different ways with different intellects.
For there is an intellect, namely, the Divine, which is Its own act of
intelligence, so that in God the understanding of His intelligence, and
the understanding of His Essence, are one and the same act, because His
Essence is His act of understanding. But there is another intellect, the
angelic, which is not its own act of understanding, as we have said above
(Question , Article ), and yet the first object of that act is the angelic
essence. Wherefore although there is a logical distinction between the
act whereby he understands that he understands, and that whereby he
understands his essence, yet he understands both by one and the same act;
because to understand his own essence is the proper perfection of his
essence, and by one and the same act is a thing, together with its
perfection, understood. And there is yet another, namely, the human
intellect, which neither is its own act of understanding, nor is its own
essence the first object of its act of understanding, for this object is
the nature of a material thing. And therefore that which is first known
by the human intellect is an object of this kind, and that which is known
secondarily is the act by which that object is known; and through the act
the intellect itself is known, the perfection of which is this act of
understanding. For this reason did the Philosopher assert that objects
are known before acts, and acts before powers (De Anima ii, 4).
Reply to Objection 1: The object of the intellect is something universal, namely,
"being" and "the true," in which the act also of understanding is
comprised. Wherefore the intellect can understand its own act. But not
primarily, since the first object of our intellect, in this state of
life, is not every being and everything true, but "being" and "true," as
considered in material things, as we have said above (Question , Article ), from
which it acquires knowledge of all other things.
Reply to Objection 2: The intelligent act of the human intellect is not the act
and perfection of the material nature understood, as if the nature of the
material thing and intelligent act could be understood by one act; just
as a thing and its perfection are understood by one act. Hence the act
whereby the intellect understands a stone is distinct from the act
whereby it understands that it understands a stone; and so on. Nor is
there any difficulty in the intellect being thus potentially infinite, as
explained above (Question , Article ).
Reply to Objection 3: The proper sense feels by reason of the immutation in the
material organ caused by the external sensible. A material object,
however, cannot immute itself; but one is immuted by another, and
therefore the act of the proper sense is perceived by the common sense.
The intellect, on the contrary, does not perform the act of understanding
by the material immutation of an organ; and so there is no comparison.
Article 4: Whether the intellect understands the act of the will?
Objection 1: It would seem that the intellect does not understand the act of
the will. For nothing is known by the intellect, unless it be in some way
present in the intellect. But the act of the will is not in the
intellect; since the will and the intellect are distinct. Therefore the
act of the will is not known by the intellect.
Objection 2: Further, the act is specified by the object. But the object of
the will is not the same as the object of the intellect. Therefore the
act of the will is specifically distinct from the object of the
intellect, and therefore the act of the will is not known by the
Objection 3: Augustine (Confess. x, 17) says of the soul's affections that
"they are known neither by images as bodies are known; nor by their
presence, like the arts; but by certain notions." Now it does not seem
that there can be in the soul any other notions of things but either the
essences of things known or the likenesses thereof. Therefore it seems
impossible for the intellect to known such affections of the soul as the
acts of the will.
On the contrary, Augustine says (De Trin. x, 11), "I understand that I
I answer that, As stated above (Question , Article ), the act of the will is
nothing but an inclination consequent on the form understood; just as the
natural appetite is an inclination consequent on the natural form. Now
the inclination of a thing resides in it according to its mode of
existence; and hence the natural inclination resides in a natural thing
naturally, and the inclination called the sensible appetite is in the
sensible thing sensibly; and likewise the intelligible inclination, which
is the act of the will, is in the intelligent subject intelligibly as in
its principle and proper subject. Hence the Philosopher expresses himself
thus (De Anima iii, 9)---that "the will is in the reason." Now whatever
is intelligibly in an intelligent subject, is understood by that
subject. Therefore the act of the will is understood by the intellect,
both inasmuch as one knows that one wills; and inasmuch as one knows the
nature of this act, and consequently, the nature of its principle which
is the habit or power.
Reply to Objection 1: This argument would hold good if the will and the intellect
were in different subjects, as they are distinct powers; for then
whatever was in the will would not be in the intellect. But as both are
rooted in the same substance of the soul, and since one is in a certain
way the principle of the other, consequently what is in the will is, in a
certain way, also in the intellect.
Reply to Objection 2: The "good" and the "true" which are the objects of the will
and of the intellect, differ logically, but one is contained in the
other, as we have said above (Question , Article , ad 1; Question , Article , ad 1); for
the true is good and the good is true. Therefore the objects of the will
fall under the intellect, and those of the intellect can fall under the
Reply to Objection 3: The affections of the soul are in the intellect not by
similitude only, like bodies; nor by being present in their subject, as
the arts; but as the thing caused is in its principle, which contains
some notion of the thing caused. And so Augustine says that the soul's
affections are in the memory by certain notions.