ld be numbered among
common notions. For by substance they would understand that which exists
in itself, and is concerned through itself--_i.e._, the knowledge of
which does not require the knowledge of anything as antecedent to it.
But by modification they would understand that which is in another
thing, the conception of which is formed by the conception of the thing
in which it is, or to which it belongs. We can have, therefore, correct
ideas of non-existent modifications, because, although out of the
understanding they have no reality, yet their essence is so comprehended
in that of another, that they can be conceived through this other.
The truth of substance (out of the understanding) lies nowhere but in
itself, because it is conceived _per se_. If therefore any one says
he has a clear idea of substance, and yet doubt whether such substance
exist, this would be as much as to say that he has a true idea, and
nevertheless doubts whether it be not false (as a little attention
sufficiently manifests;) or if any man affirms substance to be created,
he at the same time affirms that a true idea has become false, than
which nothing can be more absurd. Hence it is necessarily confessed that
the existence of substance, as well as its essence, is an eternal truth.
And hence we must conclude that there is only one substance possessing
the same attribute, which requires here a fuller development. I note
therefore--1. That the correct definition of a thing includes and
expresses nothing but the nature of the thing defined. From which
follows--2. That no definition includes or expresses a distinct number
of individuals, because it expresses nothing but the nature of the thing
defined; _ergo_, the definition of a triangle expresses no more than the
nature of a triangle, and not any fixed number of triangles. 3. There
must necessarily be a distinct cause for the existence of every existing
thing. 4. This cause, by reason of which anything exists, must either be
contained in the nature and definition of the existing thing (viz., that
it pertains to its nature to exist,) or else must be beyond it--must be
something different from it.

"As therefore it pertains to the nature of substance to exist, so must
its definition include a necessary existence, and consequently from
its sole definition we must conclude its existence. But as from its
definition, as already shown in notes two and three, it is not possible
to conclude the existenc