This effort, when it is related to the mind alone, is called _will_, but when it is related at the same time both to the mind and the body, is called _appetite_, which is therefore nothing but the very essence of man, from the nature of which necessarily follow those things which promote his preservation, and thus he is determined to do those things. Hence there is no difference between appetite and desire, unless in this particular, that desire is generally related to men in so far as they are conscious of their appetites, and it may therefore be defined as appetite of which we are conscious. From what has been said it is plain, therefore, that we neither strive for, wish, seek, nor desire anything because we think it to be good, but, on the contrary, we adjudge a thing to be good because we strive for, wish, seek, or desire it. II _Joy and Sorrow_ If anything increases, diminishes, helps, or limits our body's power of action, the idea of that thing increases, diminishes, helps, or limits our mind's power of thought. We thus see that the mind can suffer great changes, and can pass now to a greater and now to a lesser perfection; these passions explaining to us the emotions of joy and sorrow. By _joy_, therefore, in what follows, I shall understand the passion by which the mind passes to a greater perfection; by _sorrow_, on the other hand, the passion by which it passes to a less perfection. The emotion of joy, related at the same time both to the mind and the body, I call _pleasurable excitement_ (_titillatio_) or _cheerfulness_; that of sorrow I call _pain_ or _melancholy_. It is, however, to be observed that pleasurable excitement and pain are related to a man when one of his parts is affected more than the others; cheerfulness and melancholy, on the other hand, when all parts are equally affected. What the nature of desire is I have explained; and besides these three--joy, sorrow, and desire--I know of no other primary emotion, the others springing from these. _Definitions of the Principal Emotions_ I.--_Desire_ is the essence itself of man in so far as it is conceived as determined to any action by any one of his modifications.