By the vivacity of the idea we interest the fancy, and produce, though in a lesser degree, the same pleasure, which arises from a moderate passion.

As the vivacity of the idea gives pleasure, so its certainty prevents uneasiness, by fixing one particular idea in the mind, and keeping it from wavering in the choice of its objects.

It is a quality of human nature, which is conspicuous on many occasions, and is common both to the mind and body, that too sudden and violent a change is unpleasant to us, and that however any objects may in themselves be indifferent, yet their alteration gives uneasiness.

As it is the nature of doubt to cause a variation in the thought, and transport us suddenly from one idea to another, it must of consequence be the occasion of pain.

This pain chiefly takes place, where interest, relation, or the greatness and novelty of any event interests us in it.