Pleasurable excitement is joy, which, in so far as it is related to the body, consists in this, that one or some of the parts of the body are affected more than others. The power of this emotion may, therefore, be so great as to overcome the other actions of the body. It may cling obstinately to the body; it may impede the body in such a manner as to render it less capable of being affected in many ways, and therefore may be evil. Again, pain, which, on the contrary, is sorrow, considered in itself alone cannot be good. But because its power and increase is limited by the power of an external cause compared with our own power, we can therefore conceive infinite degrees of strength of this emotion, and infinite kinds of it, and we can therefore conceive it to be such that it can restrain an excess of pleasurable excitement, and so far (by the first part of this proposition) preventing the body from becoming less capable. So far, therefore, will pain be good. Love is joy with the accompanying idea of an external cause. Pleasurable excitement, therefore with the accompanying idea of an external cause, is love, and therefore love may be excessive. Again, desire is greater as the emotion from which it springs is greater. Inasmuch, therefore, as an emotion may overpower the other actions of a man, so also the desire which springs from this emotion may also overpower the other desires, and may therefore exist in the same excess which we have shown (in the preceding proposition) that pleasurable excitement possesses. Cheerfulness, which I have affirmed to be good, is more easily imagined than observed; for the emotions by which we are daily agitated are generally related to some part of the body which is affected more than the others, and therefore it is that the emotions exist for the most part in excess, and so hold the mind down to the contemplation of one object alone, that it can think about nothing else; and although men are subject to a number of emotions, and therefore few are found who are always under the control of one and the same emotion, there are not wanting those to whom one and the same emotion obstinately clings. We see men sometimes so affected by one object, that although it is not present, they believe it to be before them; and if this happens to a man who is not asleep, we say that he is delirious or mad. Nor are those believed to be less mad who are inflamed by love, dreaming about nothing but a mistress or harlot day and night, for they excite our laughter. But the avaricious man who thinks of nothing else but gain or money, and the ambitious man who thinks of nothing but glory, inasmuch as they do harm, and are, therefore, thought worthy of hatred, are not believed to be mad. In truth, however, avarice, lust, etc., are a kind of madness, although they are not reckoned amongst diseases. IV _The Evil Emotions_