The difference, therefore, of our conduct in preferring the greater number depends not upon our passions, but upon custom, and general rules.

We have found in a multitude of instances, that the augmenting the numbers of any sum augments the passion, where the numbers are precise and the difference sensible.

The mind can perceive from its immediate feeling, that three guineas produce a greater passion than two; and this it transfers to larger numbers, because of the resemblance; and by a general rule assigns to a thousand guineas, a stronger passion than to nine hundred and ninety nine.

These general rules we shall explain presently.
But beside these two species of probability, which a-re derived from an imperfect experience and from contrary causes, there is a third arising from ANALOGY, which differs from them in some material circumstances.
According to the hypothesis above explained all kinds of reasoning from causes or effects are founded on two particulars, viz., the constant conjunction of any two objects in all past experience, and the resemblance of a present object to any one of them.

The effect of these two particulars is, that the present object invigorates and inlivens the imagination; and the resemblance, along with the constant union, conveys this force and vivacity to the related idea; which we are therefore said to believe, or assent to.