she could not
express, discern betwixt Divine revelations, and the dreams of her
own soul." Now prophecy is a Divine revelation, as stated above (A.
3). Therefore the prophet always distinguishes what he says by the
spirit of prophecy, from what he says by his own spirit.

Obj. 2: Further, God commands nothing impossible, as Jerome
[*Pelagius. Ep. xvi, among the supposititious works of St. Jerome]
says. Now the prophets were commanded (Jer. 23:28): "The prophet that
hath a dream, let him tell a dream; and he that hath My word, let him
speak My word with truth." Therefore the prophet can distinguish what
he has through the spirit of prophecy from what he sees otherwise.

Obj. 3: Further, the certitude resulting from a Divine light is
greater than that which results from the light of natural reason. Now
he that has science, by the light of natural reason knows for certain
that he has it. Therefore he that has prophecy by a Divine light is
much more certain that he has it.

_On the contrary,_ Gregory says (Hom. i super Ezech.): "It must be
observed that sometimes the holy prophets, when consulted, utter
certain things by their own spirit, through being much accustomed to
prophesying, and think they are speaking by the prophetic spirit."

_I answer that,_ The prophet's mind is instructed by God in two ways:
in one way by an express revelation, in another way by a most
mysterious instinct to "which the human mind is subjected without
knowing it," as Augustine says (Gen. ad lit. ii, 17). Accordingly the
prophet has the greatest certitude about those things which he knows
by an express revelation, and he has it for certain that they are
revealed to him by God; wherefore it is written (Jer. 26:15): "In
truth the Lord sent me to you, to speak all these words in your
hearing." Else, were he not certain about this, the faith which
relies on the utterances of the prophet would not be certain. A sign
of the prophet's certitude may be gathered from the fact that Abraham
being admonished in a prophetic vision, prepared to sacrifice his
only-begotten son, which he nowise would have done had he not been
most certain of the Divine revelation.

On the other hand, his position with regard to the things he knows by
instinct is sometimes such that he is unable to distinguish fully
whether his thoughts are conceived of Divine instinct or of his own
spirit. And those things which we know by Divine instinct are not all
manifested with pro