distinguish the superior vivacity of the image arising from the superior number, where the difference is so inconsiderable.  We have a parallel instance in the affections.  It is evident, according to the principles above-mentioned, that when an object produces any passion in us, which varies according to the different quantity of the object; I say, it is evident, that the passion, properly speaking, is not a simple emotion, but a compounded one, of a great number of weaker passions, derived from a view of each part of the object.  For otherwise it were impossible the passion should encrease by the encrease of these parts.  Thus a man, who desires a thousand pound, has in reality a thousand or more desires which uniting together, seem to make only one passion; though the composition evidently betrays itself upon every alteration of the object, by the preference he gives to the larger number, if superior only by an unite.  Yet nothing can be more certain, than that so small a difference would not be discernible in the passions, nor coued render them distinguishable from each other.  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.  If you weaken either the union or resemblance, you weaken the principle of transition, and of consequence that belief, which arises from it.  The vivacity of the first impression cannot be fully conveyed to the related idea, either where the conjunction of their objects is not constant, or where the present impression does not perfectly resemble any of those, whose union we are accustomed to observe.  In those probabilities of chance and causes above-explained, it is the constancy of the union, which is diminished; and in the probability