n or other.

The reason of this is, that as stated in the First Part (Q. 110, A.
3), the corporeal nature has a natural aptitude to be moved locally
by the spiritual nature: so that the devil can produce all those
effects which can result from the local movement of bodies here
below, except he be restrained by the Divine power. Now the
representation of forms to the imagination is due, sometimes, to
local movement: for the Philosopher says (De Somno et Vigil.) [*De
Insomn. iii, iv.] that "when an animal sleeps, the blood descends in
abundance to the sensitive principle, and the movements descend with
it, viz. the impressions left by the action of sensible objects,
which impressions are preserved by means of sensible species, and
continue to move the apprehensive principle, so that they appear just
as though the sensitive principles were being affected by them at the
time." Hence such a local movement of the vital spirits or humors can
be procured by the demons, whether man sleep or wake: and so it
happens that man's imagination is brought into play.

In like manner, the sensitive appetite is incited to certain passions
according to certain fixed movements of the heart and the vital
spirits: wherefore the devil can cooperate in this also. And through
certain passions being aroused in the sensitive appetite, the result
is that man more easily perceives the movement or sensible image
which is brought in the manner explained, before the apprehensive
principle, since, as the Philosopher observes (De Somno et Virgil.:
De Insomn. iii, iv), "lovers are moved, by even a slight likeness, to
an apprehension of the beloved." It also happens, through the rousing
of a passion, that what is put before the imagination, is judged, as
being something to be pursued, because, to him who is held by a
passion, whatever the passion inclines him to, seems good. In this
way the devil induces man inwardly to sin.

Reply Obj. 1: Although vital functions are always from an intrinsic
principle, yet an extrinsic agent can cooperate with them, even as
external heat cooperates with the functions of the vegetal soul, that
food may be more easily digested.

Reply Obj. 2: This apparition of imaginary forms is not altogether
outside the order of nature, nor is it due to a command alone, but
according to local movement, as explained above.

Consequently the Reply to the Third Objection is clear, because these
forms are received originally from the se