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Thomas Aquinas. Summa Theologica, Part I (Prima Pars) From the Complete American Edition.


Language: English

Table of Contents:


(In Eight Articles)

We now have to consider the acts of the soul in regard to the
intellectual and the appetitive powers: for the other powers of the
soul do not come directly under the consideration of the theologian.
Furthermore, the acts of the appetitive part of the soul come under
the consideration of the science of morals; wherefore we shall treat
of them in the second part of this work, to which the consideration
of moral matters belongs. But of the acts of the intellectual part
we shall treat now.

In treating of these acts we shall proceed in the following order:
First, we shall inquire how the soul understands when united to the
body; secondly, how it understands when separated therefrom.

The former of these inquiries will be threefold:

(1) How the soul understands bodies which are beneath it;

(2) How it understands itself and things contained in itself;

(3) How it understands immaterial substances, which are above it.

In treating of the knowledge of corporeal things there are three
points to be considered:

(1) Through what does the soul know them?

(2) How and in what order does it know them?

(3) What does it know in them?

Under the first head there are eight points of inquiry:

(1) Whether the soul knows bodies through the intellect?

(2) Whether it understands them through its essence, or through any

(3) If through some species, whether the species of all things
intelligible are naturally innate in the soul?

(4) Whether these species are derived by the soul from certain
separate immaterial forms?

(5) Whether our soul sees in the eternal ideas all that it

(6) Whether it acquires intellectual knowledge from the senses?

(7) Whether the intellect can, through the species of which it is
possessed, actually understand, without turning to the phantasms?

(8) Whether the judgment of the intellect is hindered by an obstacle
in the sensitive powers?

FIRST ARTICLE [I, Q. 84, Art. 1]

Whether the Soul Knows Bodies Through the Intellect?

Objection 1: It would seem that the soul does not know bodies through
the intellect. For Augustine says (Soliloq. ii, 4) that "bodies cannot
be understood by the intellect; nor indeed anything corporeal unless
it can be perceived by the senses." He says also (Gen. ad lit. xii,
24) that intellectual vision is of those things that are in the soul
by their essence. But such are not bodies. Therefore the soul cannot
know bodies through the intellect.

Obj. 2: Further, as sense is to the intelligible, so is the intellect
to the sensible. But the soul can by no means, through the senses,
understand spiritual things, which are intelligible. Therefore by no
means can it, through the intellect, know bodies, which are sensible.

Obj. 3: Further, the intellect is concerned with things that are
necessary and unchangeable. But all bodies are mobile and changeable.
Therefore the soul cannot know bodies through the intellect.

_On the contrary,_ Science is in the intellect. If, therefore, the
intellect does not know bodies, it follows that there is no science of
bodies; and thus perishes natural science, which treats of mobile

_I answer that,_ It should be said in order to elucidate this
question, that the early philosophers, who inquired into the natures
of things, thought there was nothing in the world save bodies. And
because they observed that all bodies are mobile, and considered them
to be ever in a state of flux, they were of opinion that we can have
no certain knowledge of the true nature of things. For what is in a
continual state of flux, cannot be grasped with any degree of
certitude, for it passes away ere the mind can form a judgment
thereon: according to the saying of Heraclitus, that "it is not
possible twice to touch a drop of water in a passing torrent," as
the Philosopher relates (Metaph. iv, Did. iii, 5).

After these came Plato, who, wishing to save the certitude of our
knowledge of truth through the intellect, maintained that, besides
these things corporeal, there is another genus of beings, separate
from matter and movement, which beings he called species or
"ideas," by participation of which each one of these singular and
sensible things is said to be either a man, or a horse, or the like.
Wherefore he said that sciences and definitions, and whatever
appertains to the act of the intellect, are not referred to these
sensible bodies, but to those beings immaterial and separate: so
that according to this the soul does not understand these corporeal
things, but the separate species thereof.

Now this may be shown to be false for two reasons. First, because,
since those species are immaterial and immovable, knowledge of
movement and matter would be excluded from science (which knowledge
is proper to natural science), and likewise all demonstration through
moving and material causes. Secondly, because it seems ridiculous,
when we seek for knowledge of things which are to us manifest, to
introduce other beings, which cannot be the substance of those
others, since they differ from them essentially: so that granted that
we have a knowledge of those separate substances, we cannot for that
reason claim to form a judgment concerning these sensible things.

Now it seems that Plato strayed from the truth because, having
observed that all knowledge takes place through some kind of
similitude, he thought that the form of the thing known must of
necessity be in the knower in the same manner as in the thing known.
Then he observed that the form of the thing understood is in the
intellect under conditions of universality, immateriality, and
immobility: which is apparent from the very operation of the
intellect, whose act of understanding has a universal extension, and
is subject to a certain amount of necessity: for the mode of action
corresponds to the mode of the agent's form. Wherefore he concluded
that the things which we understand must have in themselves an
existence under the same conditions of immateriality and immobility.

But there is no necessity for this. For even in sensible things it is
to be observed that the form is otherwise in one sensible than in
another: for instance, whiteness may be of great intensity in one,
and of a less intensity in another: in one we find whiteness with
sweetness, in another without sweetness. In the same way the sensible
form is conditioned differently in the thing which is external to the
soul, and in the senses which receive the forms of sensible things
without receiving matter, such as the color of gold without receiving
gold. So also the intellect, according to its own mode, receives
under conditions of immateriality and immobility, the species of
material and mobile bodies: for the received is in the receiver
according to the mode of the receiver. We must conclude, therefore,
that through the intellect the soul knows bodies by a knowledge which
is immaterial, universal, and necessary.

Reply Obj. 1: These words of Augustine are to be understood as
referring to the medium of intellectual knowledge, and not to its
object. For the intellect knows bodies by understanding them, not
indeed through bodies, nor through material and corporeal species;
but through immaterial and intelligible species, which can be in the
soul by their own essence.

Reply Obj. 2: As Augustine says (De Civ. Dei xxii, 29), it is not
correct to say that as the sense knows only bodies so the intellect
knows only spiritual things; for it follows that God and the angels
would not know corporeal things. The reason of this diversity is that
the lower power does not extend to those things that belong to the
higher power; whereas the higher power operates in a more excellent
manner those things which belong to the lower power.

Reply Obj. 3: Every movement presupposes something immovable: for
when a change of quality occurs, the substance remains unmoved; and
when there is a change of substantial form, matter remains unmoved.
Moreover the various conditions of mutable things are themselves
immovable; for instance, though Socrates be not always sitting, yet
it is an immovable truth that whenever he does sit he remains in one
place. For this reason there is nothing to hinder our having an
immovable science of movable things.

SECOND ARTICLE [I, Q. 84, Art. 2]

Whether the Soul Understands Corporeal Things Through Its Essence?

Objection 1: It would seem that the soul understands corporeal things
through its essence. For Augustine says (De Trin. x, 5) that the soul
"collects and lays hold of the images of bodies which are formed in
the soul and of the soul: for in forming them it gives them something
of its own substance." But the soul understands bodies by images of
bodies. Therefore the soul knows bodies through its essence, which it
employs for the formation of such images, and from which it forms

Obj. 2: Further, the Philosopher says (De Anima iii, 8) that "the
soul, after a fashion, is everything." Since, therefore, like is known
by like, it seems that the soul knows corporeal things through itself.

Obj. 3: Further, the soul is superior to corporeal creatures. Now
lower things are in higher things in a more eminent way than in
themselves, as Dionysius says (Coel. Hier. xii). Therefore all
corporeal creatures exist in a more excellent way in the soul than in
themselves. Therefore the soul can know corporeal creatures through
its essence.

_On the contrary,_ Augustine says (De Trin. ix, 3) that "the mind
gathers knowledge of corporeal things through the bodily senses." But
the soul itself cannot be known through the bodily senses. Therefore
it does not know corporeal things through itself.

_I answer that,_ The ancient philosophers held that the soul knows
bodies through its essence. For it was universally admitted that
"like is known by like." But they thought that the form of the thing
known is in the knower in the same mode as in the thing known. The
Platonists however were of a contrary opinion. For Plato, having
observed that the intellectual soul has an immaterial nature, and an
immaterial mode of knowledge, held that the forms of things known
subsist immaterially. While the earlier natural philosophers,
observing that things known are corporeal and material, held that
things known must exist materially even in the soul that knows them.
And therefore, in order to ascribe to the soul a knowledge of all
things, they held that it has the same nature in common with all. And
because the nature of a result is determined by its principles, they
ascribed to the soul the nature of a principle; so that those who
thought fire to be the principle of all, held that the soul had the
nature of fire; and in like manner as to air and water. Lastly,
Empedocles, who held the existence of our four material elements and
two principles of movement, said that the soul was composed of these.
Consequently, since they held that things exist in the soul
materially, they maintained that all the soul's knowledge is
material, thus failing to discern intellect from sense.

But this opinion will not hold. First, because in the material
principle of which they spoke, the various results do not exist save
in potentiality. But a thing is not known according as it is in
potentiality, but only according as it is in act, as is shown
_Metaph._ ix (Did. viii, 9): wherefore neither is a power known
except through its act. It is therefore insufficient to ascribe to
the soul the nature of the principles in order to explain the fact
that it knows all, unless we further admit in the soul natures and
forms of each individual result, for instance, of bone, flesh, and
the like; thus does Aristotle argue against Empedocles (De Anima i,
5). Secondly, because if it were necessary for the thing known to
exist materially in the knower, there would be no reason why things
which have a material existence outside the soul should be devoid of
knowledge; why, for instance, if by fire the soul knows fire, that
fire also which is outside the soul should not have knowledge of fire.

We must conclude, therefore, that material things known must needs
exist in the knower, not materially, but immaterially. The reason of
this is, because the act of knowledge extends to things outside the
knower: for we know things even that are external to us. Now by
matter the form of a thing is determined to some one thing. Wherefore
it is clear that knowledge is in inverse ratio of materiality. And
consequently things that are not receptive of forms save materially,
have no power of knowledge whatever--such as plants, as the
Philosopher says (De Anima ii, 12). But the more immaterially a thing
receives the form of the thing known, the more perfect is its
knowledge. Therefore the intellect which abstracts the species not
only from matter, but also from the individuating conditions of
matter, has more perfect knowledge than the senses, which receive the
form of the thing known, without matter indeed, but subject to
material conditions. Moreover, among the senses, sight has the most
perfect knowledge, because it is the least material, as we have
remarked above (Q. 78, A. 3): while among intellects the more perfect
is the more immaterial.

It is therefore clear from the foregoing, that if there be an
intellect which knows all things by its essence, then its essence
must needs have all things in itself immaterially; thus the early
philosophers held that the essence of the soul, that it may know all
things, must be actually composed of the principles of all material
things. Now this is proper to God, that His Essence comprise all
things immaterially as effects pre-exist virtually in their cause.
God alone, therefore, understands all things through His Essence:
but neither the human soul nor the angels can do so.

Reply Obj. 1: Augustine in that passage is speaking of an imaginary
vision, which takes place through the image of bodies. To the
formation of such images the soul gives part of its substance, just
as a subject is given in order to be informed by some form. In this
way the soul makes such images from itself; not that the soul or some
part of the soul be turned into this or that image; but just as we
say that a body is made into something colored because of its being
informed with color. That this is the sense, is clear from what
follows. For he says that the soul "keeps something"--namely, not
informed with such image--"which is able freely to judge of the
species of these images": and that this is the "mind" or "intellect."
And he says that the part which is informed with these
images--namely, the imagination--is "common to us and beasts."

Reply Obj. 2: Aristotle did not hold that the soul is actually
composed of all things, as did the earlier philosophers; he said that
the soul is all things, "after a fashion," forasmuch as it is in
potentiality to all--through the senses, to all things
sensible--through the intellect, to all things intelligible.

Reply Obj. 3: Every creature has a finite and determinate essence.
Wherefore although the essence of the higher creature has a certain
likeness to the lower creature, forasmuch as they have something in
common generically, yet it has not a complete likeness thereof,
because it is determined to a certain species other than the species
of the lower creature. But the Divine Essence is a perfect likeness
of all, whatsoever may be found to exist in things created, being the
universal principle of all.

THIRD ARTICLE [I, Q. 84, Art. 3]

Whether the Soul Understands All Things Through Innate Species?

Objection 1: It would seem that the soul understands all things
through innate species. For Gregory says, in a homily for the
Ascension (xxix in Ev.), that "man has understanding in common with
the angels." But angels understand all things through innate species:
wherefore in the book _De Causis_ it is said that "every intelligence
is full of forms." Therefore the soul also has innate species of
things, by means of which it understands corporeal things.

Obj. 2: Further, the intellectual soul is more excellent than
corporeal primary matter. But primary matter was created by God under
the forms to which it has potentiality. Therefore much more is the
intellectual soul created by God under intelligible species. And so
the soul understands corporeal things through innate species.

Obj. 3: Further, no one can answer the truth except concerning what
he knows. But even a person untaught and devoid of acquired
knowledge, answers the truth to every question if put to him in
orderly fashion, as we find related in the Meno (xv seqq.) of Plato,
concerning a certain individual. Therefore we have some knowledge of
things even before we acquire knowledge; which would not be the case
unless we had innate species. Therefore the soul understands
corporeal things through innate species.

_On the contrary,_ The Philosopher, speaking of the intellect, says
(De Anima iii, 4) that it is like "a tablet on which nothing is

_I answer that,_ Since form is the principle of action, a thing must
be related to the form which is the principle of an action, as it is
to that action: for instance, if upward motion is from lightness,
then that which only potentially moves upwards must needs be only
potentially light, but that which actually moves upwards must needs
be actually light. Now we observe that man sometimes is only a
potential knower, both as to sense and as to intellect. And he is
reduced from such potentiality to act--through the action of sensible
objects on his senses, to the act of sensation--by instruction or
discovery, to the act of understanding. Wherefore we must say that
the cognitive soul is in potentiality both to the images which are
the principles of sensing, and to those which are the principles of
understanding. For this reason Aristotle (De Anima iii, 4) held that
the intellect by which the soul understands has no innate species,
but is at first in potentiality to all such species.

But since that which has a form actually, is sometimes unable to act
according to that form on account of some hindrance, as a light thing
may be hindered from moving upwards; for this reason did Plato hold
that naturally man's intellect is filled with all intelligible
species, but that, by being united to the body, it is hindered from
the realization of its act. But this seems to be unreasonable. First,
because, if the soul has a natural knowledge of all things, it seems
impossible for the soul so far to forget the existence of such
knowledge as not to know itself to be possessed thereof: for no man
forgets what he knows naturally; that, for instance, the whole is
larger than the part, and such like. And especially unreasonable does
this seem if we suppose that it is natural to the soul to be united
to the body, as we have established above ([Q. 76] , A. 1): for it is
unreasonable that the natural operation of a thing be totally
hindered by that which belongs to it naturally. Secondly, the
falseness of this opinion is clearly proved from the fact that if a
sense be wanting, the knowledge of what is apprehended through that
sense is wanting also: for instance, a man who is born blind can have
no knowledge of colors. This would not be the case if the soul had
innate images of all intelligible things. We must therefore conclude
that the soul does not know corporeal things through innate species.

Reply Obj. 1: Man indeed has intelligence in common with the angels,
but not in the same degree of perfection: just as the lower grades of
bodies, which merely exist, according to Gregory (Homily on
Ascension, xxix In Ev.), have not the same degree of perfection as
the higher bodies. For the matter of the lower bodies is not totally
completed by its form, but is in potentiality to forms which it has
not: whereas the matter of heavenly bodies is totally completed by
its form, so that it is not in potentiality to any other form, as we
have said above (Q. 66, A. 2). In the same way the angelic intellect
is perfected by intelligible species, in accordance with its nature;
whereas the human intellect is in potentiality to such species.

Reply Obj. 2: Primary matter has substantial being through its form,
consequently it had need to be created under some form: else it would
not be in act. But when once it exists under one form it is in
potentiality to others. On the other hand, the intellect does not
receive substantial being through the intelligible species; and
therefore there is no comparison.

Reply Obj. 3: If questions be put in an orderly fashion they proceed
from universal self-evident principles to what is particular. Now by
such a process knowledge is produced in the mind of the learner.
Wherefore when he answers the truth to a subsequent question, this is
not because he had knowledge previously, but because he thus learns
for the first time. For it matters not whether the teacher proceed
from universal principles to conclusions by questioning or by
asserting; for in either case the mind of the listener is assured of
what follows by that which preceded.

FOURTH ARTICLE [I, Q. 84, Art. 4]

Whether the Intelligible Species Are Derived by the Soul from Certain
Separate Forms?

Objection 1: It would seem that the intelligible species are derived
by the soul from some separate forms. For whatever is such by
participation is caused by what is such essentially; for instance,
that which is on fire is reduced to fire as the cause thereof. But
the intellectual soul forasmuch as it is actually understanding,
participates the thing understood: for, in a way, the intellect in
act is the thing understood in act. Therefore what in itself and in
its essence is understood in act, is the cause that the intellectual
soul actually understands. Now that which in its essence is actually
understood is a form existing without matter. Therefore the
intelligible species, by which the soul understands, are caused by
some separate forms.

Obj. 2: Further, the intelligible is to the intellect, as the
sensible is to the sense. But the sensible species which are in the
senses, and by which we sense, are caused by the sensible object
which exists actually outside the soul. Therefore the intelligible
species, by which our intellect understands, are caused by some
things actually intelligible, existing outside the soul. But these
can be nothing else than forms separate from matter. Therefore the
intelligible forms of our intellect are derived from some separate

Obj. 3: Further, whatever is in potentiality is reduced to act by
something actual. If, therefore, our intellect, previously in
potentiality, afterwards actually understands, this must needs be
caused by some intellect which is always in act. But this is a
separate intellect. Therefore the intelligible species, by which we
actually understand, are caused by some separate substances.

_On the contrary,_ If this were true we should not need the senses in
order to understand. And this is proved to be false especially from
the fact that if a man be wanting in a sense, he cannot have any
knowledge of the sensibles corresponding to that sense.

_I answer that,_ Some have held that the intelligible species of our
intellect are derived from certain separate forms or substances. And
this in two ways. For Plato, as we have said (A. 1), held that the
forms of sensible things subsist by themselves without matter; for
instance, the form of a man which he called _per se_ man, and the
form or idea of a horse which is called _per se_ horse, and so forth.
He said therefore that these forms are participated both by our soul
and by corporeal matter; by our soul, to the effect of knowledge
thereof, and by corporeal matter to the effect of existence: so that,
just as corporeal matter by participating the idea of a stone,
becomes an individuating stone, so our intellect, by participating
the idea of a stone, is made to understand a stone. Now participation
of an idea takes place by some image of the idea in the participator,
just as a model is participated by a copy. So just as he held that
the sensible forms, which are in corporeal matter, are derived from
the ideas as certain images thereof: so he held that the intelligible
species of our intellect are images of the ideas, derived therefrom.
And for this reason, as we have said above (A. 1), he referred
sciences and definitions to those ideas.

But since it is contrary to the nature of sensible things that their
forms should subsist without matter, as Aristotle proves in many ways
(Metaph. vi), Avicenna (De Anima v) setting this opinion aside, held
that the intelligible species of all sensible things, instead of
subsisting in themselves without matter, pre-exist immaterially in the
separate intellects: from the first of which, said he, such species
are derived by a second, and so on to the last separate intellect
which he called the "active intelligence," from which, according to
him, intelligible species flow into our souls, and sensible species
into corporeal matter. And so Avicenna agrees with Plato in this, that
the intelligible species of our intellect are derived from certain
separate forms; but these Plato held to subsist of themselves, while
Avicenna placed them in the "active intelligence." They differ, too,
in this respect, that Avicenna held that the intelligible species do
not remain in our intellect after it has ceased actually to
understand, and that it needs to turn (to the active intellect) in
order to receive them anew. Consequently he does not hold that the
soul has innate knowledge, as Plato, who held that the participated
ideas remain immovably in the soul.

But in this opinion no sufficient reason can be assigned for the soul
being united to the body. For it cannot be said that the intellectual
soul is united to the body for the sake of the body: for neither is
form for the sake of matter, nor is the mover for the sake of the
moved, but rather the reverse. Especially does the body seem necessary
to the intellectual soul, for the latter's proper operation which is
to understand: since as to its being the soul does not depend on the
body. But if the soul by its very nature had an inborn aptitude for
receiving intelligible species through the influence of only certain
separate principles, and were not to receive them from the senses, it
would not need the body in order to understand: wherefore to no
purpose would it be united to the body.

But if it be said that our soul needs the senses in order to
understand, through being in some way awakened by them to the
consideration of those things, the intelligible species of which it
receives from the separate principles: even this seems an insufficient
explanation. For this awakening does not seem necessary to the soul,
except in as far as it is overcome by sluggishness, as the Platonists
expressed it, and by forgetfulness, through its union with the body:
and thus the senses would be of no use to the intellectual soul except
for the purpose of removing the obstacle which the soul encounters
through its union with the body. Consequently the reason of the union
of the soul with the body still remains to be sought.

And if it be said with Avicenna, that the senses are necessary to
the soul, because by them it is aroused to turn to the "active
intelligence" from which it receives the species: neither is this
a sufficient explanation. Because if it is natural for the soul to
understand through species derived from the "active intelligence,"
it follows that at times the soul of an individual wanting in one
of the senses can turn to the active intelligence, either from the
inclination of its very nature, or through being roused by another
sense, to the effect of receiving the intelligible species of which
the corresponding sensible species are wanting. And thus a man born
blind could have knowledge of colors; which is clearly untrue. We
must therefore conclude that the intelligible species, by which our
soul understands, are not derived from separate forms.

Reply Obj. 1: The intelligible species which are participated by our
intellect are reduced, as to their first cause, to a first principle
which is by its essence intelligible--namely, God. But they proceed
from that principle by means of the sensible forms and material
things, from which we gather knowledge, as Dionysius says (Div. Nom.

Reply Obj. 2: Material things, as to the being which they have
outside the soul, may be actually sensible, but not actually
intelligible. Wherefore there is no comparison between sense and

Reply Obj. 3: Our passive intellect is reduced from potentiality to
act by some being in act, that is, by the active intellect, which is
a power of the soul, as we have said (Q. 79, A. 4); and not by a
separate intelligence, as proximate cause, although perchance as
remote cause.

FIFTH ARTICLE [I, Q. 84, Art. 5]

Whether the Intellectual Soul Knows Material Things in the Eternal

Objection 1: It would seem that the intellectual soul does not know
material things in the eternal types. For that in which anything is
known must itself be known more and previously. But the intellectual
soul of man, in the present state of life, does not know the eternal
types: for it does not know God in Whom the eternal types exist, but
is "united to God as to the unknown," as Dionysius says (Myst.
Theolog. i). Therefore the soul does not know all in the eternal

Obj. 2: Further, it is written (Rom. 1:20) that "the invisible things
of God are clearly seen . . . by the things that are made." But among
the invisible things of God are the eternal types. Therefore the
eternal types are known through creatures and not the converse.

Obj. 3: Further, the eternal types are nothing else but ideas, for
Augustine says (QQ. 83, qu. 46) that "ideas are permanent types
existing in the Divine mind." If therefore we say that the
intellectual soul knows all things in the eternal types, we come back
to the opinion of Plato who said that all knowledge is derived from

_On the contrary,_ Augustine says (Confess. xii, 25): "If we both see
that what you say is true, and if we both see that what I say is
true, where do we see this, I pray? Neither do I see it in you, nor
do you see it in me: but we both see it in the unchangeable truth
which is above our minds." Now the unchangeable truth is contained in
the eternal types. Therefore the intellectual soul knows all true
things in the eternal types.

_I answer that,_ As Augustine says (De Doctr. Christ. ii, 11): "If
those who are called philosophers said by chance anything that was
true and consistent with our faith, we must claim it from them as
from unjust possessors. For some of the doctrines of the heathens are
spurious imitations or superstitious inventions, which we must be
careful to avoid when we renounce the society of the heathens."
Consequently whenever Augustine, who was imbued with the doctrines of
the Platonists, found in their teaching anything consistent with
faith, he adopted it: and those thing which he found contrary to
faith he amended. Now Plato held, as we have said above (A. 4), that
the forms of things subsist of themselves apart from matter; and
these he called ideas, by participation of which he said that our
intellect knows all things: so that just as corporeal matter by
participating the idea of a stone becomes a stone, so our intellect,
by participating the same idea, has knowledge of a stone. But since
it seems contrary to faith that forms of things themselves, outside
the things themselves and apart from matter, as the Platonists held,
asserting that _per se_ life or _per se_ wisdom are creative
substances, as Dionysius relates (Div. Nom. xi); therefore Augustine
(QQ. 83, qu. 46), for the ideas defended by Plato, substituted the
types of all creatures existing in the Divine mind, according to
which types all things are made in themselves, and are known to the
human soul.

When, therefore, the question is asked: Does the human soul know all
things in the eternal types? we must reply that one thing is said to
be known in another in two ways. First, as in an object itself known;
as one may see in a mirror the images of things reflected therein. In
this way the soul, in the present state of life, cannot see all
things in the eternal types; but the blessed who see God, and all
things in Him, thus know all things in the eternal types. Secondly,
one thing is said to be known in another as in a principle of
knowledge: thus we might say that we see in the sun what we see by
the sun. And thus we must needs say that the human soul knows all
things in the eternal types, since by participation of these types we
know all things. For the intellectual light itself which is in us, is
nothing else than a participated likeness of the uncreated light, in
which are contained the eternal types. Whence it is written (Ps. 4:6,
7), "Many say: Who showeth us good things?" which question the
Psalmist answers, "The light of Thy countenance, O Lord, is signed
upon us," as though he were to say: By the seal of the Divine light
in us, all things are made known to us.

But since besides the intellectual light which is in us, intelligible
species, which are derived from things, are required in order for us
to have knowledge of material things; therefore this same knowledge
is not due merely to a participation of the eternal types, as the
Platonists held, maintaining that the mere participation of ideas
sufficed for knowledge. Wherefore Augustine says (De Trin. iv, 16):
"Although the philosophers prove by convincing arguments that all
things occur in time according to the eternal types, were they able
to see in the eternal types, or to find out from them how many kinds
of animals there are and the origin of each? Did they not seek for
this information from the story of times and places?"

But that Augustine did not understand all things to be known in their
"eternal types" or in the "unchangeable truth," as though the eternal
types themselves were seen, is clear from what he says (QQ. 83, qu.
46)--viz. that "not each and every rational soul can be said to be
worthy of that vision," namely, of the eternal types, "but only those
that are holy and pure," such as the souls of the blessed.

From what has been said the objections are easily solved.

SIXTH ARTICLE [I, Q. 84, Art. 6]

Whether Intellectual Knowledge Is Derived from Sensible Things?

Objection 1: It would seem that intellectual knowledge is not derived
from sensible things. For Augustine says (QQ. 83, qu. 9) that "we
cannot expect to learn the fulness of truth from the senses of the
body." This he proves in two ways. First, because "whatever the
bodily senses reach, is continually being changed; and what is never
the same cannot be perceived." Secondly, because, "whatever we
perceive by the body, even when not present to the senses, may be
present to the imagination, as when we are asleep or angry: yet we
cannot discern by the senses, whether what we perceive be the
sensible object or the deceptive image thereof. Now nothing can be
perceived which cannot be distinguished from its counterfeit." And so
he concludes that we cannot expect to learn the truth from the
senses. But intellectual knowledge apprehends the truth. Therefore
intellectual knowledge cannot be conveyed by the senses.

Obj. 2: Further, Augustine says (Gen. ad lit. xii, 16): "We must not
think that the body can make any impression on the spirit, as though
the spirit were to supply the place of matter in regard to the body's
action; for that which acts is in every way more excellent than that
which it acts on." Whence he concludes that "the body does not cause
its image in the spirit, but the spirit causes it in itself."
Therefore intellectual knowledge is not derived from sensible things.

Obj. 3: Further, an effect does not surpass the power of its cause.
But intellectual knowledge extends beyond sensible things: for we
understand some things which cannot be perceived by the senses.
Therefore intellectual knowledge is not derived from sensible things.

_On the contrary,_ The Philosopher says (Metaph. i, 1; Poster. ii,
15) that the principle of knowledge is in the senses.

_I answer that,_ On this point the philosophers held three opinions.
For Democritus held that "all knowledge is caused by images issuing
from the bodies we think of and entering into our souls," as
Augustine says in his letter to Dioscorus (cxviii, 4). And Aristotle
says (De Somn. et Vigil.) that Democritus held that knowledge is
caused by a "discharge of images." And the reason for this opinion
was that both Democritus and the other early philosophers did not
distinguish between intellect and sense, as Aristotle relates (De
Anima iii, 3). Consequently, since the sense is affected by the
sensible, they thought that all our knowledge is affected by this
mere impression brought about by sensible things. Which impression
Democritus held to be caused by a discharge of images.

Plato, on the other hand, held that the intellect is distinct from
the senses: and that it is an immaterial power not making use of a
corporeal organ for its action. And since the incorporeal cannot be
affected by the corporeal, he held that intellectual knowledge is not
brought about by sensible things affecting the intellect, but by
separate intelligible forms being participated by the intellect, as
we have said above (AA. 4 ,5). Moreover he held that sense is a power
operating of itself. Consequently neither is sense, since it is a
spiritual power, affected by the sensible: but the sensible organs
are affected by the sensible, the result being that the soul is in a
way roused to form within itself the species of the sensible.
Augustine seems to touch on this opinion (Gen. ad lit. xii, 24) where
he says that the "body feels not, but the soul through the body,
which it makes use of as a kind of messenger, for reproducing within
itself what is announced from without." Thus according to Plato,
neither does intellectual knowledge proceed from sensible knowledge,
nor sensible knowledge exclusively from sensible things; but these
rouse the sensible soul to the sentient act, while the senses rouse
the intellect to the act of understanding.

Aristotle chose a middle course. For with Plato he agreed that
intellect and sense are different. But he held that the sense has not
its proper operation without the cooperation of the body; so that to
feel is not an act of the soul alone, but of the "composite." And he
held the same in regard to all the operations of the sensitive part.
Since, therefore, it is not unreasonable that the sensible objects
which are outside the soul should produce some effect in the
"composite," Aristotle agreed with Democritus in this, that the
operations of the sensitive part are caused by the impression of the
sensible on the sense: not by a discharge, as Democritus said, but by
some kind of operation. For Democritus maintained that every
operation is by way of a discharge of atoms, as we gather from _De
Gener._ i, 8. But Aristotle held that the intellect has an operation
which is independent of the body's cooperation. Now nothing corporeal
can make an impression on the incorporeal. And therefore in order to
cause the intellectual operation according to Aristotle, the
impression caused by the sensible does not suffice, but something
more noble is required, for "the agent is more noble than the
patient," as he says (De Gener. i, 5). Not, indeed, in the sense that
the intellectual operation is effected in us by the mere impression
of some superior beings, as Plato held; but that the higher and more
noble agent which he calls the active intellect, of which we have
spoken above (Q. 79, AA. 3, 4) causes the phantasms received from the
senses to be actually intelligible, by a process of abstraction.

According to this opinion, then, on the part of the phantasms,
intellectual knowledge is caused by the senses. But since the
phantasms cannot of themselves affect the passive intellect, and
require to be made actually intelligible by the active intellect, it
cannot be said that sensible knowledge is the total and perfect cause
of intellectual knowledge, but rather that it is in a way the
material cause.

Reply Obj. 1: Those words of Augustine mean that we must not expect
the entire truth from the senses. For the light of the active
intellect is needed, through which we achieve the unchangeable truth
of changeable things, and discern things themselves from their

Reply Obj. 2: In this passage Augustine speaks not of intellectual
but of imaginary knowledge. And since, according to the opinion of
Plato, the imagination has an operation which belongs to the soul
only, Augustine, in order to show that corporeal images are impressed
on the imagination, not by bodies but by the soul, uses the same
argument as Aristotle does in proving that the active intellect must
be separate, namely, because "the agent is more noble than the
patient." And without doubt, according to the above opinion, in the
imagination there must needs be not only a passive but also an active
power. But if we hold, according to the opinion of Aristotle, that
the action of the imagination is an action of the "composite," there
is no difficulty; because the sensible body is more noble than the
organ of the animal, in so far as it is compared to it as a being in
act to a being in potentiality; even as the object actually colored
is compared to the pupil which is potentially colored. It may,
however, be said, although the first impression of the imagination is
through the agency of the sensible, since "fancy is movement produced
in accordance with sensation" (De Anima iii, 3), that nevertheless
there is in man an operation which by synthesis and analysis forms
images of various things, even of things not perceived by the senses.
And Augustine's words may be taken in this sense.

Reply Obj. 3: Sensitive knowledge is not the entire cause of
intellectual knowledge. And therefore it is not strange that
intellectual knowledge should extend further than sensitive knowledge.

SEVENTH ARTICLE [I, Q. 84, Art. 7]

Whether the Intellect Can Actually Understand Through the
Intelligible Species of Which It Is Possessed, Without Turning to
the Phantasms?

Objection 1: It would seem that the intellect can actually understand
through the intelligible species of which it is possessed, without
turning to the phantasms. For the intellect is made actual by the
intelligible species by which it is informed. But if the intellect is
in act, it understands. Therefore the intelligible species suffices
for the intellect to understand actually, without turning to the

Obj. 2: Further, the imagination is more dependent on the senses
than the intellect on the imagination. But the imagination can
actually imagine in the absence of the sensible. Therefore much more
can the intellect understand without turning to the phantasms.

Obj. 3: There are no phantasms of incorporeal things: for the
imagination does not transcend time and space. If, therefore, our
intellect cannot understand anything actually without turning to the
phantasms, it follows that it cannot understand anything incorporeal.
Which is clearly false: for we understand truth, and God, and the

_On the contrary,_ The Philosopher says (De Anima iii, 7) that "the
soul understands nothing without a phantasm."

_I answer that,_ In the present state of life in which the soul is
united to a passible body, it is impossible for our intellect to
understand anything actually, except by turning to the phantasms.
First of all because the intellect, being a power that does not make
use of a corporeal organ, would in no way be hindered in its act
through the lesion of a corporeal organ, if for its act there were
not required the act of some power that does make use of a corporeal
organ. Now sense, imagination and the other powers belonging to the
sensitive part, make use of a corporeal organ. Wherefore it is clear
that for the intellect to understand actually, not only when it
acquires fresh knowledge, but also when it applies knowledge already
acquired, there is need for the act of the imagination and of the
other powers. For when the act of the imagination is hindered by a
lesion of the corporeal organ, for instance in a case of frenzy; or
when the act of the memory is hindered, as in the case of lethargy, we
see that a man is hindered from actually understanding things of which
he had a previous knowledge. Secondly, anyone can experience this of
himself, that when he tries to understand something, he forms certain
phantasms to serve him by way of examples, in which as it were he
examines what he is desirous of understanding. For this reason it is
that when we wish to help someone to understand something, we lay
examples before him, from which he forms phantasms for the purpose of

Now the reason of this is that the power of knowledge is proportioned
to the thing known. Wherefore the proper object of the angelic
intellect, which is entirely separate from a body, is an intelligible
substance separate from a body. Whereas the proper object of the human
intellect, which is united to a body, is a quiddity or nature existing
in corporeal matter; and through such natures of visible things it
rises to a certain knowledge of things invisible. Now it belongs to
such a nature to exist in an individual, and this cannot be apart from
corporeal matter: for instance, it belongs to the nature of a stone to
be in an individual stone, and to the nature of a horse to be in an
individual horse, and so forth. Wherefore the nature of a stone or any
material thing cannot be known completely and truly, except in as much
as it is known as existing in the individual. Now we apprehend the
individual through the senses and the imagination. And, therefore, for
the intellect to understand actually its proper object, it must of
necessity turn to the phantasms in order to perceive the universal
nature existing in the individual. But if the proper object of our
intellect were a separate form; or if, as the Platonists say, the
natures of sensible things subsisted apart from the individual; there
would be no need for the intellect to turn to the phantasms whenever
it understands.

Reply Obj. 1: The species preserved in the passive intellect exist
there habitually when it does not understand them actually, as we
have said above (Q. 79, A. 6). Wherefore for us to understand
actually, the fact that the species are preserved does not suffice;
we need further to make use of them in a manner befitting the things
of which they are the species, which things are natures existing in

Reply Obj. 2: Even the phantasm is the likeness of an individual
thing; wherefore the imagination does not need any further likeness
of the individual, whereas the intellect does.

Reply Obj. 3: Incorporeal things, of which there are no phantasms,
are known to us by comparison with sensible bodies of which there are
phantasms. Thus we understand truth by considering a thing of which
we possess the truth; and God, as Dionysius says (Div. Nom. i), we
know as cause, by way of excess and by way of remotion. Other
incorporeal substances we know, in the present state of life, only by
way of remotion or by some comparison to corporeal things. And,
therefore, when we understand something about these things, we need
to turn to phantasms of bodies, although there are no phantasms of
the things themselves.

EIGHTH ARTICLE [I, Q. 84, Art. 8]

Whether the Judgment of the Intellect Is Hindered Through Suspension
of the Sensitive Powers?

Objection 1: It would seem that the judgment of the intellect is not
hindered by suspension of the sensitive powers. For the superior does
not depend on the inferior. But the judgment of the intellect is
higher than the senses. Therefore the judgment of the intellect is
not hindered through suspension of the senses.

Obj. 2: Further, to syllogize is an act of the intellect. But during
sleep the senses are suspended, as is said in _De Somn. et Vigil._ i
and yet it sometimes happens to us to syllogize while asleep.
Therefore the judgment of the intellect is not hindered through
suspension of the senses.

_On the contrary,_ What a man does while asleep, against the moral
law, is not imputed to him as a sin; as Augustine says (Gen. ad lit.
xii, 15). But this would not be the case if man, while asleep, had
free use of his reason and intellect. Therefore the judgment of the
intellect is hindered by suspension of the senses.

_I answer that,_ As we have said above (A. 7), our intellect's proper
and proportionate object is the nature of a sensible thing. Now a
perfect judgment concerning anything cannot be formed, unless all
that pertains to that thing's nature be known; especially if that be
ignored which is the term and end of judgment. Now the Philosopher
says (De Coel. iii), that "as the end of a practical science is
action, so the end of natural science is that which is perceived
principally through the senses"; for the smith does not seek
knowledge of a knife except for the purpose of action, in order that
he may produce a certain individual knife; and in like manner the
natural philosopher does not seek to know the nature of a stone and
of a horse, save for the purpose of knowing the essential properties
of those things which he perceives with his senses. Now it is clear
that a smith cannot judge perfectly of a knife unless he knows the
action of the knife: and in like manner the natural philosopher
cannot judge perfectly of natural things, unless he knows sensible
things. But in the present state of life whatever we understand, we
know by comparison to natural sensible things. Consequently it is not
possible for our intellect to form a perfect judgment, while the
senses are suspended, through which sensible things are known to us.

Reply Obj. 1: Although the intellect is superior to the senses,
nevertheless in a manner it receives from the senses, and its first
and principal objects are founded in sensible things. And therefore
suspension of the senses necessarily involves a hindrance to the
judgment of the intellect.

Reply Obj. 2: The senses are suspended in the sleeper through certain
evaporations and the escape of certain exhalations, as we read in _De
Somn. et Vigil._ iii. And, therefore, according to the amount of such
evaporation, the senses are more or less suspended. For when the
amount is considerable, not only are the senses suspended, but also
the imagination, so that there are no phantasms; thus does it happen,
especially when a man falls asleep after eating and drinking
copiously. If, however, the evaporation be somewhat less, phantasms
appear, but distorted and without sequence; thus it happens in a case
of fever. And if the evaporation be still more attenuated, the
phantasms will have a certain sequence: thus especially does it
happen towards the end of sleep in sober men and those who are gifted
with a strong imagination. If the evaporation be very slight, not
only does the imagination retain its freedom, but also the common
sense is partly freed; so that sometimes while asleep a man may judge
that what he sees is a dream, discerning, as it were, between things,
and their images. Nevertheless, the common sense remains partly
suspended; and therefore, although it discriminates some images from
the reality, yet is it always deceived in some particular. Therefore,
while man is asleep, according as sense and imagination are free, so
is the judgment of his intellect unfettered, though not entirely.
Consequently, if a man syllogizes while asleep, when he wakes up he
invariably recognizes a flaw in some respect.