a reason or cause must be
granted for its existence; if, on the contrary, it does not
exist, a cause must also be granted, which prevents it from
existing, or annuls its existence. This reason or cause must
either be contained in the nature of the thing in question, or be
external to it. For instance, the reason for the non--existence
of a square circle is indicated in its nature, namely, because it
would involve a contradiction. On the other hand, the existence
of substance follows also solely from its nature, inasmuch as its
nature involves existence. (See Prop. vii.)

But the reason for the existence of a triangle or a circle
does not follow from the nature of those figures, but from the
order of universal nature in extension. From the latter it must
follow, either that a triangle necessarily exists, or that it is
impossible that it should exist. So much is self--evident. It
follows therefrom that a thing necessarily exists, if no cause or
reason be granted which prevents its existence.

If, then, no cause or reason can be given, which prevents the
existence of God, or which destroys his existence, we must
certainly conclude that he necessarily does exist. If such a
reason or cause should be given, it must either be drawn from the
very nature of God, or be external to him--that is, drawn from
another substance of another nature. For if it were of the same
nature, God, by that very fact, would be admitted to exist. But
substance of another nature could have nothing in common with God
(by Prop. ii.), and therefore would be unable either to cause or
to destroy his existence.

As, then, a reason or cause which would annul the divine
existence cannot be drawn from anything external to the divine
nature, such cause must perforce, if God does not exist, be drawn
from God's own nature, which would involve a contradiction. To
make such an affirmation about a being absolutely infinite and
supremely perfect is absurd; therefore, neither in the nature of
God, nor externally to his nature, can a cause or reason be
assigned which would annul his existence. Therefore, God
necessarily exists. Q.E.D.

Another proof.--The potentiality of non--existence is a
negation of power, and contrariwise the potentiality of existence
is a power, as is obvious. If, then, that which necessarily
exists is nothing but finite beings, such finite beings are more
powerful than a being absolutely infinite, which is obviously
absurd