SECOND ARTICLE [I, Q. 54, Art. 2]

Whether in the Angel to Understand Is to Exist?

Objection 1: It would seem that in the angel to understand is to

exist. For in living things to live is to be, as the Philosopher says

(De Anima ii, text. 37). But to "understand is in a sense to live"

(De Anima ii, text. 37). Therefore in the angel to understand is to

exist.

Obj. 2: Further, cause bears the same relation to cause, as effect to

effect. But the form whereby the angel exists is the same as the form

by which he understands at least himself. Therefore in the angel to

understand is to exist.

_On the contrary,_ The angel's act of understanding is his movement,

as is clear from Dionysius (Div. Nom. iv). But to exist is not

movement. Therefore in the angel to be is not to understand.

_I answer that,_ The action of the angel, as also the action of any

creature, is not his existence. For as it is said (Metaph. ix, text.

16), there is a twofold class of action; one which passes out to

something beyond, and causes passion in it, as burning and cutting;

and another which does not pass outwards, but which remains within the

agent, as to feel, to understand, to will; by such actions nothing

outside is changed, but the whole action takes place within the agent.

It is quite clear regarding the first kind of action that it cannot be

the agent's very existence: because the agent's existence is signified

as within him, while such an action denotes something as issuing from

the agent into the thing done. But the second action of its own nature

has infinity, either simple or relative. As an example of simple

infinity, we have the act "to understand," of which the object is "the

true"; and the act "to will," of which the object is "the good"; each

of which is convertible with being; and so, to understand and to will,

of themselves, bear relation to all things, and each receives its

species from its object. But the act of sensation is relatively

infinite, for it bears relation to all sensible things; as sight does

to all things visible. Now the being of every creature is restricted

to one in genus and species; God's being alone is simply infinite,

comprehending all things in itself, as Dionysius says (Div. Nom. v).

Hence the Divine nature alone is its own act of understanding and its

own act of will.

Reply Obj. 1: Life is sometimes taken for the existence of the living

subject: sometimes also for a vital operation, that is, for one

whereby something is shown to be living. In this way the Philosopher

says that to understand is, in a sense, to live: for there he

distinguishes the various grades of living things according to the

various functions of life.

Reply Obj. 2: The essence of an angel is the reason of his entire

existence, but not the reason of his whole act of understanding,

since he cannot understand everything by his essence. Consequently

in its own specific nature as such an essence, it is compared to the

existence of the angel, whereas to his act of understanding it is

compared as included in the idea of a more universal object, namely,

truth and being. Thus it is evident, that, although the form is the

same, yet it is not the principle of existence and of understanding

according to the same formality. On this account it does not follow

that in the angel "to be" is the same as 'to understand.'

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Summa Theologica, Part I (Prima Pars) From the Complete American Edition · 第 350 / 722 题