from the clear and
distinct conception of anything, does not necessarily belong to it in
reality. Let us therefore set an object clearly before us, let us sever
it in thought so far as is possible from all other objects, and we shall
at once be able to determine what properties and relations are essential
and what are not essential to it. And if we find empirically that any
object manifests a property or relation not involved in the clear and
distinct conception of it, we can say with certainty that such property
or relation does not belong to it except by arbitrary arrangement, or,
in other words, by the external combination of things which in their own
nature have no affinity or connexion.

Now, by the application of this principle, we might at once assure
ourselves of many mathematical truths; but, as has been already shown,
there is a point of view from which we may doubt even these, so long as
the idea of a God that deceives us is not excluded. If it is not certain
that there is a God that cannot lie, it is not certain that there is an
objective matter in space to which mathematical truth applies. But the
existence of God may be proved in two ways. In the first place, it may
be proved through the principle of causality, which is a self-evident
truth. We have in our mind many ideas, and according to the principle of
causality, all these ideas must be derived from something that contains
a "formal" reality which corresponds to their "objective" reality, i.e.
which contains at least as much reality in its existence out of thought
as they contain in their existence in thought. Now we might derive from
ourselves not only the ideas of other minds like ourselves, but possibly
also of material objects, since these are lower in the scale of
existence than ourselves, and it is conceivable that the idea of them
might be got by omitting some of the qualities which distinguish
ourselves. But the idea of God, of a being who is eternal and immutable,
all-powerful, all-wise, and all-good, cannot be derived from our own
limited and imperfect existence. The origin, therefore, must be sought
in a being who contains actually in himself all that is contained in our
idea of him.

Descartes's metaphysics.

It was objected by some of the critics of Descartes that the idea of
God as the infinite Being is merely negative, and that it is derived
from the finite simply by abstracting from its conditions. Descartes
answers th