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Objection 1: It would seem that the human soul in the present state
of life can understand immaterial substances in themselves. For
Augustine (De Trin. ix, 3) says: "As the mind itself acquires
the knowledge of corporeal things by means of the corporeal senses, so
it gains from itself the knowledge of incorporeal things." But these
are the immaterial substances. Therefore the human mind understands
immaterial substances.
Objection 2: Further, like is known by like. But the human mind
is more akin to immaterial than to material things; since its own
nature is immaterial, as is clear from what we have said above
(Question 76, Article 1). Since then our mind understands
material things, much more is it able to understand immaterial things.
Objection 3: Further, the fact that objects which are in themselves
most sensible are not most felt by us, comes from sense being corrupted
by their very excellence. But the intellect is not subject to such a
corrupting influence from its object, as is stated De Anima iii,
4. Therefore things which are in themselves in the highest degree of
intelligibility, are likewise to us most intelligible. As material
things, however, are intelligible only so far as we make them actually
so by abstracting them from material conditions, it is clear that those
substances are more intelligible in themselves whose nature is
immaterial. Therefore they are much more known to us than are material
things.
Objection 4: Further, the Commentator says (Metaph. ii) that
"nature would be frustrated in its end" were we unable to understand
abstract substances, "because it would have made what in itself is
naturally intelligible not to be understood at all." But in nature
nothing is idle or purposeless. Therefore immaterial substances can be
understood by us.
Objection 5: Further, as sense is to the sensible, so is intellect
to the intelligible. But our sight can see all things corporeal,
whether superior and incorruptible; or lower and corruptible.
Therefore our intellect can understand all intelligible substances,
even the superior and immaterial.
On the contrary, It is written (Wis. 9:16): "The things
that are in heaven, who shall search out?" But these substances are
said to be in heaven, according to Mt. 18:10, "Their angels
in heaven," etc. Therefore immaterial substances cannot be known by
human investigation.
I answer that, In the opinion of Plato, immaterial substances are
not only understood by us, but are the objects we understand first of
all. For Plato taught that immaterial subsisting forms, which he
called "Ideas," are the proper objects of our intellect, and thus
first and "per se" understood by us; and, further, that material
objects are known by the soul inasmuch as phantasy and sense are mixed
up with the mind. Hence the purer the intellect is, so much the more
clearly does it perceive the intelligible truth of immaterial things.
But in Aristotle's opinion, which experience corroborates, our
intellect in its present state of life has a natural relationship to the
natures of material things; and therefore it can only understand by
turning to the phantasms, as we have said above (Question 84,
Article 7). Thus it clearly appears that immaterial substances
which do not fall under sense and imagination, cannot first and "per
se" be known by us, according to the mode of knowledge which
experience proves us to have.
Nevertheless Averroes (Comment. De Anima iii) teaches that in
this present life man can in the end arrive at the knowledge of separate
substances by being coupled or united to some separate substance, which
he calls the "active intellect," and which, being a separate
substance itself, can naturally understand separate substances.
Hence, when it is perfectly united to us so that by its means we are
able to understand perfectly, we also shall be able to understand
separate substances, as in the present life through the medium of the
passive intellect united to us, we can understand material things.
Now he said that the active intellect is united to us, thus. For
since we understand by means of both the active intellect and
intelligible objects, as, for instance, we understand conclusions by
principles understood; it is clear that the active intellect must be
compared to the objects understood, either as the principal agent is to
the instrument, or as form to matter. For an action is ascribed to
two principles in one of these two ways; to a principal agent and to an
instrument, as cutting to the workman and the saw; to a form and its
subject, as heating to heat and fire. In both these ways the active
intellect can be compared to the intelligible object as perfection is to
the perfectible, and as act is to potentiality. Now a subject is made
perfect and receives its perfection at one and the same time, as the
reception of what is actually visible synchronizes with the reception of
light in the eye. Therefore the passive intellect receives the
intelligible object and the active intellect together; and the more
numerous the intelligible objects received, so much the nearer do we
come to the point of perfect union between ourselves and the active
intellect; so much so that when we understand all the intelligible
objects, the active intellect becomes one with us, and by its
instrumentality we can understand all things material and immaterial.
In this he makes the ultimate happiness of man to consist. Nor, as
regards the present inquiry, does it matter whether the passive
intellect in that state of happiness understands separate substances by
the instrumentality of the active intellect, as he himself maintains,
or whether (as he says Alexander holds) the passive intellect can
never understand separate substances (because according to him it is
corruptible), but man understands separate substances by means of the
active intellect.
This opinion, however, is untrue. First, because, supposing the
active intellect to be a separate substance, we could not formally
understand by its instrumentality, for the medium of an agent's formal
action consists in its form and act, since every agent acts according
to its actuality, as was said of the passive intellect (Question
70, Article 1). Secondly, this opinion is untrue, because in
the above explanation, the active intellect, supposing it to be a
separate substance, would not be joined to us in its substance, but
only in its light, as participated in things understood; and would not
extend to the other acts of the active intellect so as to enable us to
understand immaterial substances; just as when we see colors set off by
the sun, we are not united to the substance of the sun so as to act
like the sun, but its light only is united to us, that we may see the
colors. Thirdly, this opinion is untrue, because granted that, as
above explained, the active intellect were united to us in substance,
still it is not said that it is wholly so united in regard to one
intelligible object, or two; but rather in regard to all intelligible
objects. But all such objects together do not equal the force of the
active intellect, as it is a much greater thing to understand separate
substances than to understand all material things. Hence it clearly
follows that the knowledge of all material things would not make the
active intellect to be so united to us as to enable us by its
instrumentality to understand separate substances.
Fourthly, this opinion is untrue, because it is hardly possible for
anyone in this world to understand all material things: and thus no
one, or very few, could reach to perfect felicity; which is against
what the Philosopher says (Ethic. i, 9), that happiness is a
"kind of common good, communicable to all capable of virtue."
Further, it is unreasonable that only the few of any species attain to
the end of the species.
Fifthly, the Philosopher expressly says (Ethic. i, 10), that
happiness is "an operation according to perfect virtue"; and after
enumerating many virtues in the tenth book, he concludes (Ethic. i,
7) that ultimate happiness consisting in the knowledge of the highest
things intelligible is attained through the virtue of wisdom, which in
the sixth chapter he had named as the chief of speculative sciences.
Hence Aristotle clearly places the ultimate felicity of man in the
knowledge of separate substances, obtainable by speculative science;
and not by being united to the active intellect as some imagined.
Sixthly, as was shown above (Question 79, Article 4), the
active intellect is not a separate substance; but a faculty of the
soul, extending itself actively to the same objects to which the
passive intellect extends receptively; because, as is stated (De
Anima iii, 5), the passive intellect is "all things
potentially," and the active intellect is "all things in act."
Therefore both intellects, according to the present state of life,
extend to material things only, which are made actually intelligible by
the active intellect, and are received in the passive intellect.
Hence in the present state of life we cannot understand separate
immaterial substances in themselves, either by the passive or by the
active intellect.
Reply to Objection 1: Augustine may be taken to mean that the
knowledge of incorporeal things in the mind can be gained by the mind
itself. This is so true that philosophers also say that the knowledge
concerning the soul is a principle for the knowledge of separate
substances. For by knowing itself, it attains to some knowledge of
incorporeal substances, such as is within its compass; not that the
knowledge of itself gives it a perfect and absolute knowledge of them.
Reply to Objection 2: The likeness of nature is not a sufficient
cause of knowledge; otherwise what Empedocles said would be true
---that the soul needs to have the nature of all in order to know
all. But knowledge requires that the likeness of the thing known be in
the knower, as a kind of form thereof. Now our passive intellect, in
the present state of life, is such that it can be informed with
similitudes abstracted from phantasms: and therefore it knows material
things rather than immaterial substances.
Reply to Objection 3: There must needs be some proportion between
the object and the faculty of knowledge; such as of the active to the
passive, and of perfection to the perfectible. Hence that sensible
objects of great power are not grasped by the senses, is due not merely
to the fact that they corrupt the organ, but also to their being
improportionate to the sensitive power. And thus it is that immaterial
substances are improportionate to our intellect, in our present state
of life, so that it cannot understand them.
Reply to Objection 4: This argument of the Commentator fails in
several ways. First, because if separate substances are not
understood by us, it does not follow that they are not understood by
any intellect; for they are understood by themselves, and by one
another.
Secondly, to be understood by us is not the end of separate
substances: while only that is vain and purposeless, which fails to
attain its end. It does not follow, therefore, that immaterial
substances are purposeless, even if they are not understood by us at
all.
Reply to Objection 5: Sense knows bodies, whether superior or
inferior, in the same way, that is, by the sensible acting on the
organ. But we do not understand material and immaterial substances in
the same way. The former we understand by a process of abstraction,
which is impossible in the case of the latter, for there are no
phantasms of what is immaterial.
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