THIRD ARTICLE [I, Q. 87, Art. 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.

Obj. 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.

Obj. 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 understand."

_I answer that,_ As stated above (AA. 1, 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 (Q. 79,

A. 1), 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 Obj. 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 (Q. 84, A. 7), from which it acquires knowledge

of all other things.

Reply Obj. 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 (Q. 86, A. 2).

Reply Obj. 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.

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Summa Theologica, Part I (Prima Pars) From the Complete American Edition · 第 544 / 722 题