Strictly speaking, sensation (as we've defined it) refers only to experiences of pleasure and pain. But the self also makes certain movements related to pleasure and pain – if an object causes pleasure, for example, we tend to move toward it, or in the opposite case away from it. In actuality, these movements fall more in the domain of activity than sensibility per se, but they're so closely related to sensibility that it's really quite impossible to separate them.

The tendency of the self to move in the direction of an agreeable object is called an inclination, and this definition also gives us a classification – that is, there are as many different types of inclinations as there are types of objects leading to such movements. Of these, there are three major classes: the self; other selves (our peers); and finally, certain ideas or conceptions of the mind, like the good or the beautiful. This also yields three types of inclinations: egoistic, altruistic, and higher.

The self is the object of egoistic inclinations, which are of two types. Some are purely conservative and try to keep things as they are, while others are acquisitive and seek to augment being. To conserve and to augment being are the two tendencies of nature. The first kind of inclination is called the instinct for conservation – the love of life. Whatever occurs, we find life dear, clinging to it even if it brings more pain than pleasure.