ng to Jer. 17:9: "The heart is perverse above all things, and
unsearchable; who can know it? I am the Lord, Who search the heart."
Therefore angels do not know the secrets of hearts.

_I answer that,_ A secret thought can be known in two ways: first, in
its effect. In this way it can be known not only by an angel, but also
by man; and with so much the greater subtlety according as the effect
is the more hidden. For thought is sometimes discovered not merely by
outward act, but also by change of countenance; and doctors can tell
some passions of the soul by the mere pulse. Much more then can
angels, or even demons, the more deeply they penetrate those occult
bodily modifications. Hence Augustine says (De divin. daemon.) that
demons "sometimes with the greatest faculty learn man's dispositions,
not only when expressed by speech, but even when conceived in thought,
when the soul expresses them by certain signs in the body"; although
(Retract. ii, 30) he says "it cannot be asserted how this is done."

In another way thoughts can be known as they are in the mind, and
affections as they are in the will: and thus God alone can know the
thoughts of hearts and affections of wills. The reason of this is,
because the rational creature is subject to God only, and He alone
can work in it Who is its principal object and last end: this will be
developed later (Q. 63, A. 1; Q. 105, A. 5). Consequently all that is
in the will, and all things that depend only on the will, are known
to God alone. Now it is evident that it depends entirely on the will
for anyone actually to consider anything; because a man who has a
habit of knowledge, or any intelligible species, uses them at will.
Hence the Apostle says (1 Cor. 2:11): "For what man knoweth the
things of a man, but the spirit of a man that is in him?"

Reply Obj. 1: In the present life one man's thought is not known
by another owing to a twofold hindrance; namely, on account of the
grossness of the body, and because the will shuts up its secrets.
The first obstacle will be removed at the Resurrection, and does not
exist at all in the angels; while the second will remain, and is in
the angels now. Nevertheless the brightness of the body will show
forth the quality of the soul; as to its amount of grace and of
glory. In this way one will be able to see the mind of another.

Reply Obj. 2: Although one angel sees the intelligible species of
another, by the fact that the species are proport