In short, the occurrences of life, by the time we come to know it a little, would be incapable of affecting the mind with any other sensations than those of loathing and weariness, if many things were not adapted to affect the mind by means of other powers besides novelty in them, and of other passions besides curiosity in ourselves.

These powers and passions shall be considered in their place.

But, whatever these powers are, or upon what principle soever they affect the mind, it is absolutely necessary that they should not be exerted in those things which a daily and vulgar use have brought into a stale unaffecting familiarity.

Some degree of novelty must be one of the materials in every instrument which works upon the mind; and curiosity blends itself more or less with all our passions.
SECTION II.
PAIN AND PLEASURE.
It seems, then, necessary towards moving the passions of people advanced in life to any considerable degree, that the objects designed for that purpose, besides their being in some measure new, should be capable of exciting pain or pleasure from other causes.

Pain and pleasure are simple ideas, incapable of definition.