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 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.