cleaves to the
similitudes of the things as to the things themselves. But in this
there is deception. So as a good angel cannot be the cause of
deception, it seems that he cannot cause the imaginative vision, by
changing the imagination.

_On the contrary,_ Those things which are seen in dreams are seen by
imaginative vision. But the angels reveal things in dreams, as
appears from Matt. 1:20; 2:13, 19 in regard to the angel who appeared
to Joseph in dreams. Therefore an angel can move the imagination.

_I answer that,_ Both a good and a bad angel by their own natural
power can move the human imagination. This may be explained as
follows. For it was said above (Q. 110, A. 3), that corporeal nature
obeys the angel as regards local movement, so that whatever can be
caused by the local movement of bodies is subject to the natural
power of the angels. Now it is manifest that imaginative apparitions
are sometimes caused in us by the local movement of animal spirits
and humors. Hence Aristotle says (De Somn. et Vigil.) [*De Insomniis
iii], when assigning the cause of visions in dreams, that "when an
animal sleeps, the blood descends in abundance to the sensitive
principle, and movements descend with it," that is, the impressions
left from the movements are preserved in the animal spirits, "and
move the sensitive principle"; so that a certain appearance ensues,
as if the sensitive principle were being then changed by the external
objects themselves. Indeed, the commotion of the spirits and humors
may be so great that such appearances may even occur to those who are
awake, as is seen in mad people, and the like. So, as this happens by
a natural disturbance of the humors, and sometimes also by the will
of man who voluntarily imagines what he previously experienced, so
also the same may be done by the power of a good or a bad angel,
sometimes with alienation from the bodily senses, sometimes without
such alienation.

Reply Obj. 1: The first principle of the imagination is from the
sense in act. For we cannot imagine what we have never perceived by
the senses, either wholly or partly; as a man born blind cannot
imagine color. Sometimes, however, the imagination is informed in
such a way that the act of the imaginative movement arises from the
impressions preserved within.

Reply Obj. 2: An angel changes the imagination, not indeed by the
impression of an imaginative form in no way previously received from
the senses (for he c