The first kind arises in the soul originally, from unknown causes.

The second is derived in a great measure from our ideas, and that in the following order.

An impression first strikes upon the senses, and makes us perceive heat or cold, thirst or hunger, pleasure or pain of some kind or other.

Of this impression there is a copy taken by the mind, which remains after the impression ceases; and this we call an idea.

This idea of pleasure or pain, when it returns upon the soul, produces the new impressions of desire and aversion, hope and fear, which may properly be called impressions of reflexion, because derived from it.