ed. I distinguish between truths of fact and truths of
reason. Truths of fact can only be verified by confronting them with truths
of reason, and by tracing them back to immediate perceptions within us,
such as St. Augustine and M. Descartes very promptly acknowledged to be
indubitable; that is to say, we cannot doubt that we think, nor indeed that
we think this thing or that. But in order to judge whether our inward
notions have any reality in things, and to pass from thoughts to objects,
my opinion is that it is necessary to consider whether our perceptions are
firmly connected among themselves and with others that we have had, in such
fashion as to manifest the rules of mathematics and other truths of [410]
reason. In this case one must regard them as real; and I think that it is
the only means of distinguishing them from imaginations, dreams and
visions. Thus the truth of things outside us can be recognized only through
the connexion of phenomena. The criterion of the truths of reason, or those
which spring from conceptions, is found in an exact use of the rules of
logic. As for ideas or notions, I call _real_ all those the possibility of
which is certain; and the _definitions_ which do not mark this possibility
are only _nominal_. Geometricians well versed in analysis are aware what
difference there is in this respect between several properties by which
some line or figure might be defined. Our gifted author has not gone so
far, perhaps; one may see, however, from the account I have given of him
already, and from what follows, that he is by no means lacking in
profundity or reflexion.

6. Thereafter he proceeds to examine whether motion, matter and space
spring from themselves; and to that end he considers whether it is possible
to conceive that they do not exist. He remarks upon this privilege of God,
that as soon as it is assumed that he exists it must be admitted that he
exists of necessity. This is a corollary to a remark which I made in the
little discourse mentioned above, namely that as soon as one admits that
God is possible, one must admit that he exists of necessity. Now, as soon
as one admits that God exists, one admits that he is possible. Therefore as
soon as one admits that God exists, one must admit that he exists of
necessity. Now this privilege does not belong to the three things of which
we have just spoken. The author believes also especially concerning motion,
that it is not sufficient to say, w