Thomas Aquinas

“ Therefore love is the first of the concupiscible passions.
I answer that, Good and evil are the object of the concupiscible faculty. Now good naturally precedes evil; since evil is privation of good. Wherefore all the passions, the object of which is good, are naturally before those, the object of which is evil---that is to say, each precedes its contrary passion: because the quest of a good is the reason for shunning the opposite evil. ”

“ In like manner fear, through being a movement from evil, precedes daring. And that hope and despair naturally precede fear and daring is evident from this---that as the desire of good is the reason for avoiding evil, so hope and despair are the reason for fear and daring: because daring arises from the hope of victory, and fear arises from the despair of overcoming. Lastly, anger arises from daring: for no one is angry while seeking vengeance, unless he dare to avenge himself, as Avicenna observes in the sixth book of his Physics. ”

“ And this very aptitude or proportion of the appetite to good is love, which is complacency in good; while movement towards good is desire or concupiscence; and rest in good is joy or pleasure. Accordingly in this order, love precedes desire, and desire precedes pleasure. ”

“ Consequently of all the concupiscible passions, concupiscence is felt most; and for this reason the power is named after it.
Reply to Objection 2: The union of lover and beloved is twofold. There is real union, consisting in the conjunction of one with the other. This union belongs to joy or pleasure, which follows desire. There is also an affective union, consisting in an aptitude or proportion, in so far as one thing, from the very fact of its having an aptitude for and an inclination to another, partakes of it: and love betokens such a union. ”

“ Reply to Objection 1: Because anger arises from the other passions, as an effect from the causes that precede it, it is from anger, as being more manifest than the other passions, that the power takes its name. ”

“ Consequently these cannot be principal passions; because that which is accidental cannot be said to be principal. And so neither can anger be called a principal passion, because it arises from daring. ”

“ Two of them, viz. joy and sadness, are said to be principal because in them all the other passions have their completion and end; wherefore they arise from all the other passions, as is stated in Ethic. ”