The third way is taken from possibility and necessity, and runs thus.
We find in nature things that are possible to be and not to be, since
they are found to be generated, and to corrupt, and consequently, they
are possible to be and not to be. But it is impossible for these
always to exist, for that which is possible not to be at some time is
not. Therefore, if everything is possible not to be, then at one time
there could have been nothing in existence. Now if this were true,
even now there would be nothing in existence, because that which does
not exist only begins to exist by something already existing.
Therefore, if at one time nothing was in existence, it would have been
impossible for anything to have begun to exist; and thus even now
nothing would be in existence--which is absurd. Therefore, not all
beings are merely possible, but there must exist something the
existence of which is necessary. But every necessary thing either has
its necessity caused by another, or not. Now it is impossible to go on
to infinity in necessary things which have their necessity caused by
another, as has been already proved in regard to efficient causes.
Therefore we cannot but postulate the existence of some being having
of itself its own necessity, and not receiving it from another, but
rather causing in others their necessity. This all men speak of as
God.

The fourth way is taken from the gradation to be found in things.
Among beings there are some more and some less good, true, noble and
the like. But _more_ and _less_ are predicated of different things,
according as they resemble in their different ways something which is
the maximum, as a thing is said to be hotter according as it more
nearly resembles that which is hottest; so that there is something
which is truest, something best, something noblest and, consequently,