seek to know the nature of a stone and
of a horse, save for the purpose of knowing the essential properties
of those things which he perceives with his senses. Now it is clear
that a smith cannot judge perfectly of a knife unless he knows the
action of the knife: and in like manner the natural philosopher
cannot judge perfectly of natural things, unless he knows sensible
things. But in the present state of life whatever we understand, we
know by comparison to natural sensible things. Consequently it is not
possible for our intellect to form a perfect judgment, while the
senses are suspended, through which sensible things are known to us.

Reply Obj. 1: Although the intellect is superior to the senses,
nevertheless in a manner it receives from the senses, and its first
and principal objects are founded in sensible things. And therefore
suspension of the senses necessarily involves a hindrance to the
judgment of the intellect.

Reply Obj. 2: The senses are suspended in the sleeper through certain
evaporations and the escape of certain exhalations, as we read in _De
Somn. et Vigil._ iii. And, therefore, according to the amount of such
evaporation, the senses are more or less suspended. For when the
amount is considerable, not only are the senses suspended, but also
the imagination, so that there are no phantasms; thus does it happen,
especially when a man falls asleep after eating and drinking
copiously. If, however, the evaporation be somewhat less, phantasms
appear, but distorted and without sequence; thus it happens in a case
of fever. And if the evaporation be still more attenuated, the
phantasms will have a certain sequence: thus especially does it
happen towards the end of sleep in sober men and those who are gifted
with a strong imagination. If the evaporation be very slight, not
only does the imagination retain its freedom, but also the common
sense is partly freed; so that sometimes while asleep a man may judge
that what he sees is a dream, discerning, as it were, between things,
and their images. Nevertheless, the common sense remains partly
suspended; and therefore, although it discriminates some images from
the reality, yet is it always deceived in some particular. Therefore,
while man is asleep, according as sense and imagination are free, so
is the judgment of his intellect unfettered, though not entirely.
Consequently, if a man syllogizes while asleep, when he wakes up he
invariably recognizes a flaw in so