Benedict de Spinoza, THE ETHICS
Page: 46

exclude the existence of the horse, he will necessarily regard
the horse as present: he will not be able to doubt of its
existence, although he be not certain thereof. We have daily
experience of such a state of things in dreams; and I do not
suppose that there is anyone, who would maintain that, while he
is dreaming, he has the free power of suspending his judgment
concerning the things in his dream, and bringing it about that
he should not dream those things, which he dreams that he sees;
yet it happens, notwithstanding, that even in dreams we suspend
our judgment, namely, when we dream that we are dreaming.

Further, I grant that no one can be deceived, so far as actual
perception extends--that is, I grant that the mind's
imaginations, regarded in themselves, do not involve error (II.
xvii. note); but I deny, that a man does not, in the act of
perception, make any affirmation. For what is the perception of
a winged horse, save affirming that a horse has wings? If the
mind could perceive nothing else but the winged horse, it would
regard the same as present to itself: it would have no reasons
for doubting its existence, nor any faculty of dissent, unless
the imagination of a winged horse be joined to an idea which
precludes the existence of the said horse, or unless the mind
perceives that the idea which it possess of a winged horse is
inadequate, in which case it will either necessarily deny the
existence of such a horse, or will necessarily be in doubt on
the subject.

I think that I have anticipated my answer to the third objection,
namely, that the will is something universal which is predicated
of all ideas, and that it only signifies that which is common to
all ideas, namely, an affirmation, whose adequate essence must,
therefore, in so far as it is thus conceived in the abstract, be
in every idea, and be, in this respect alone, the same in all,
not in so far as it is considered as constituting the idea's
essence: for, in this respect, particular affirmations differ
one from the other, as much as do ideas. For instance, the
affirmation which involves the idea of a circle, differs from