particular manner, either immediately or by the interposition of other
ideas. Whatever is absurd is unintelligible; nor is it possible for the
imagination to conceive any thing contrary to a demonstration. But as in
reasonings from causation, and concerning matters of fact, this absolute
necessity cannot take place, and the imagination is free to conceive both
sides of the question, I still ask, Wherein consists the deference
betwixt incredulity and belief? since in both cases the conception of the
idea is equally possible and requisite.

It will not be a satisfactory answer to say, that a person, who does not
assent to a proposition you advance; after having conceived the object in
the same manner with you; immediately conceives it in a different manner,
and has different ideas of it. This answer is unsatisfactory; not because
it contains any falshood, but because it discovers not all the truth.
It is contest, that in all cases, wherein we dissent from any person, we
conceive both sides of the question; but as we can believe only one, it
evidently follows, that the belief must make some difference betwixt that
conception to which we assent, and that from which we dissent. We may
mingle, and unite, and separate, and confound, and vary our ideas in a
hundred different ways; but until there appears some principle, which
fixes one of these different situations, we have in reality no opinion:
And this principle, as it plainly makes no addition to our precedent
ideas, can only change the manner of our conceiving them.

All the perceptions of the mind are of two kinds, viz. impressions and
ideas, which differ from each other only in their different degrees of
force and vivacity. Our ideas are copyed from our impressions, and
represent them in all their parts. When you would any way vary the idea
of a particular object, you can only encrease or diminish its force and
vivacity. If you make any other change on it, it represents a different