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 derived from analogy, it is the resemblance only, which is affected.

Without some degree of resemblance, as well as union, it is impossible there can be any reasoning: but as this resemblance admits of many different degrees, the reasoning becomes proportionably more or less firm and certain.

An experiment loses of its force, when transferred to instances, which are not exactly resembling; though it is evident it may still retain as much as may be the foundation of probability, as long as there is any resemblance remaining.
SECT.XIII.OF UNPHILOSOPHICAL PROBABILITY.
All these kinds of probability are received by philosophers, and allowed to be reasonable foundations of belief and opinion.