Being, is, or exists, as any demonstration of geometry can be.

But the reason which leads many to persuade them selves that there is a
difficulty in knowing this truth, and even also in knowing what their mind
really is, is that they never raise their thoughts above sensible objects,
and are so accustomed to consider nothing except by way of imagination,
which is a mode of thinking limited to material objects, that all that is
not imaginable seems to them not intelligible.  The truth of this is
sufficiently manifest from the single circumstance, that the philosophers
of the schools accept as a maxim that there is nothing in the
understanding which was not previously in the senses, in which however it
is certain that the ideas of God and of the soul have never been; and it
appears to me that they who make use of their imagination to comprehend
these ideas do exactly the some thing as if, in order to hear sounds or
smell odors, they strove to avail themselves of their eyes; unless indeed
that there is this difference, that the sense of sight does not afford us
an inferior assurance to those of smell or hearing; in place of which,
neither our imagination nor our senses can give us assurance of anything
unless our understanding intervene.

Finally, if there be still persons who are not sufficiently persuaded of
the existence of God and of the soul, by the reasons I have adduced, I am
desirous that they should know that all the other propositions, of the
truth of which they deem themselves perhaps more assured, as that we have
a body, and that there exist stars and an earth, and such like, are less
certain; for, although we have a moral assurance of these things, which is
so strong that there is an appearance of extravagance in doubting of their
existence, yet at the same time no one, unless his intellect is impaired,
can deny, when the question relates to a metaphysical certitude, that
there is sufficient reason to exclude entire assurance, in the observation
that when asleep we can in the same way imagine ourselves possessed of
another body and that we see other stars and another earth, when there is
nothing of the kind.  For how do we know that the thoughts which occur in
dreaming are false rather than those other which we experience when awake,
since the former are often not less vivid and distinct than the latter?
And though men of the highest genius study this question as long as they
please, I do not believe that they will be able to give any reason which
can be sufficient to remove this doubt, unless they presuppose the
existence of God.  For, in the first place even the principle which I have
already taken as a rule, viz., that all the things which we clearly and
distinctly conceive are true, is certain only because God is or exists and
because he is a Perfect Being, and because all that we possess is derived
from him:  whence it follows that our ideas or notions, which to the extent
of their clearness and distinctness are real, and proceed from God, must
to that extent be true.  Accordingly, whereas we not infrequently have ideas
or notions in which some falsity is contained, this can only be the case with
such as are to some extent confused and obscure, and in this proceed from
nothing (participate of negation), that is, exist in us thus confused because
we are not wholly perfect.  And it is evident that it is not less repugnant
that falsity or imperfection, in so far as it is imperfection, should proceed
from God, than that truth or perfection should proceed from nothing.  But if
we did not know that all which we possess of real and true proceeds from a
Perfect and Infinite Being, however clear and distinct our ideas might be,
we should have no ground on that account for the assurance that they possessed
the perfection of being true.

But after the knowledge of God and of the soul has rendered us certain of
this rule, we can easily understand that the truth of the thoughts we
experience when awake, ought not in the slightest degree to be called in
question on account of the illusions of our dreams.  For if it happened
that an individual, even when asleep, had some very distinct idea, as, for
example, if a geometer should discover some new demonstration, the
circumstance of his being asleep would not militate against its truth; and
as for the most ordinary error of our dreams, which consists in their
representing to us various objects in the same way as our external senses,
this is not prejudicial, since it leads us very properly to suspect the
truth of the ideas of sense; for we are not infrequently deceived in the
same manner when awake; as when persons in the jaundice see all objects
yellow, or when the stars or bodies at a great distance appear to us much
smaller than they are.  For, in fine, whether awake or asleep, we ought
never to allow ourselves to be persuaded of the truth of anything unless
on the evidence of our reason.  And it must be noted that I say of our
reason, and not of our imagination or of our senses:  thus, for example,
although we very clearly see the sun, we ought not therefore to determine
that it is only of the size which our sense of sight presents; and we may
very distinctly imagine the head of a lion joined to the body of a goat,
without being therefore shut up to the conclusion that a chimaera exists;
for it is not a dictate of reason that what we thus see or imagine is in
reality existent; but it plainly tells us that all our ideas or notions
contain in them some truth; for otherwise it could not be that God, who is
wholly perfect and veracious, should have placed them in us.  And because
our reasonings are never so clear or so complete during sleep as when we
are awake, although sometimes the acts of our imagination are then as
lively and distinct, if not more so than in our waking moments, reason
further dictates that, since all our thoughts cannot be true because of
our partial imperfection, those possessing truth must infallibly be found
in the experience of our waking moments rather than in that of our dreams.

PART V

I would here willingly have proceeded to exhibit the whole chain of truths
which I deduced from these primary but as with a view to this it would
have been necessary now to treat of many questions in dispute among the
earned, with whom I do not wish to be embroiled, I believe that it will be
better for me to refrain from this exposition, and only mention in general
what these truths are, that the more judicious may be able to determine
whether a more special account of them would conduce to the public
advantage.  I have ever remained firm in my original resolution to suppose
no other principle than that of which I have recently availed myself in
demonstrating the existence of God and of the soul, and to accept as true