Just as the formal object of belief is truth, so the formal object of emotion is evaluation: beliefs aim at truth, emotions at evaluation.
Just like beliefs, emotions aim at being justified, that is, at according with reality. In particular, they aim at reflecting the significance or meaning of their object for the subject.
Desires on the other hand aim at altering reality so that it comes to accord with them. Thus, whereas emotions (and beliefs) have a mind-to-world direction of fit, desires have an opposite world-to-mind direction of fit: emotions aim at reflecting reality, desires at altering it.
Emotions do seem to involve desires. If I am angry with John, surely that is because I desire him to treat me with more respect; if I am scared of the snake, surely that is because I desire to continue living.
Emotions also seem to give rise to desires, for example, to scowl at John or to kill the snake with my sabre.
Notice, however, that desires of the first kind (desires involved in emotions) differ from desires of the second kind (desires arising from emotions) in that they are more abstract or general or latent, and more akin to dispositions than desires proper.
While desires can arise from emotions, they need not do so, and come in many forms and shades, including wishes, drives, urges, impulses, compulsions, longings, cravings, and yearnings.
Properly speaking, a wish is a desire that is unlikely to be satisfied, as in, “I wish they would just shut up!” A drive is a desire that arises from the body, for example, the sex drive. An urge is a drive that has become urgent. An impulse is a sudden, unconsidered desire that is closely associated with a particular action. A compulsion is an impulse that is difficult or impossible to resist, as in obsessive-compulsive disorder. Longing is a strong and sustained desire, especially for something unattainable or hard to attain. Craving is an uncomfortable longing. And yearning is longing accompanied by tenderness or sadness.
Thus, some desires are purely physiological or biological, although even these, whether or not they be satisfied, give rise to emotions.The important thing, it seems, is to be aware which came first, the desire or the emotion, and not to rationalize our base desires as more noble emotions, which is all too common in romantic love and many other life situations.
Sometimes, of course, a desire gives rise to an emotion which gives rise to another, different desire, and so on; or an emotion gives rise to a desire which gives rise to another, different emotion—which is why, in time, the two, desire and emotion, can become so very difficult to disentangle. Desires born out of emotion and emotions born out of desire can and do take on a life of their own, and need not be less genuine for being secondary.
At this moment in time, you are reading these words because, for whatever reason or reasons, you have formed a desire to read them, and this desire motivates you to read them. ‘Motivation’, like ‘emotion’, derives from the Latin movere, ‘to move’. Though this often escapes our notice, many of our beliefs and all of our desires are born out of our feelings, whether our emotions or sensations such as hunger and pain.
Brain injured people who lack the capacity for emotions find it difficult to positively decide and desire because they lack a basis for choosing between competing options.
The philosopher David Hume famously argued that one cannot derive an ‘ought’ from an ‘is’, that is, one cannot deduce or derive moral conclusions from naked facts, and, by extension, that all moral conclusions are grounded in emotion.
Adapted from Heaven and Hell: The Psychology of the Emotions