existence is nothing different from the idea of any object, and that when
after the simple conception of any thing we would conceive it as
existent, we in reality make no addition to or alteration on our first
idea. Thus when we affirm, that God is existent, we simply form the idea
of such a being, as he is represented to us; nor is the existence, which
we attribute to him, conceived by a particular idea, which we join to the
idea of his other qualities, and can again separate and distinguish from
them. But I go farther; and not content with asserting, that the
conception of the existence of any object is no addition to the simple
conception of it, I likewise maintain, that the belief of the existence
joins no new ideas to those which compose the idea of the object. When
I think of God, when I think of him as existent, and when I believe him
to be existent, my idea of him neither encreases nor diminishes. But as
it is certain there is a great difference betwixt the simple conception of
the existence of an object, and the belief of it, and as this difference
lies not in the parts or composition of the idea, which we conceive; it
follows, that it must lie in the manner, in which we conceive it.

Suppose a person present with me, who advances propositions, to which I
do not assent, that Caesar dyed in his bed, that silver is more fusible,
than lead, or mercury heavier than gold; it is evident, that
notwithstanding my incredulity, I clearly understand his meaning, and
form all the same ideas, which he forms. My imagination is endowed with
the same powers as his; nor is it possible for him to conceive any idea,
which I cannot conceive; nor conjoin any, which I cannot conjoin. I
therefore ask, Wherein consists the difference betwixt believing and
disbelieving any proposition? The answer is easy with regard to
propositions, that are proved by intuition or demonstration. In that
case, the person, who assents, not only conceives the ideas according to
the proposition, but is necessarily determined to conceive them in that