Happiness, the end of this art, being the state of the mind arising from its several grateful perceptions or modifications, the natural course of the inquiry is to consider the various human powers, perceptions, and actions, and then to compare them so as to find what really constitutes happiness, and how it may be attained.

The principles that first display themselves in childhood are the external senses, with some small powers of spontaneous motion, introducing to the mind perceptions of pleasure and pain, which becoming forthwith the object of desire and aversion, are our first notions of natural good and evil.

Next to Ideas of Sensation, we acquire Concomitant ideas of Sensation from two or more senses together--number, extension, &c.

Ideas of consciousness or reflection, which is another natural power of perception, complete the list of the materials of knowledge; to which, when the powers of judging and reasoning are added, all the main acts of the understanding are given.
There are still, however, some finer perceptions, that may be left over until the will is disposed of.
Under the head of Will, he notes first the facts of Desire and Aversion, being new motions of the soul, distinct from, though arising out of, sensations, perceptions, and judgments.

To these it is common to add Joy and Sorrow, arising in connexion with desire, though they partake more of sensations than of volitions.