On every subject, my boy, there is one method of beginning, for those who mean to deliberate well; they must know what the thing is about which the deliberation is to be, or else of necessity go altogether astray. But it has escaped the notice of most men that they do not know the essence of each several thing. As if they did know, then, they do not agree with each other at the outset of the enquiry, and as they proceed they pay the probable penalty, for they agree neither with themselves nor with each other. Let not you and I, then, fall into the error which we condemn in others, but since the question proposed to us is, whether we ought rather to enter into a friendship with one who is in love or not, having by mutual agreement settled on a definition of love, what it is, and what power it has, and looking back and referring to this, let us prosecute our enquiry whether it occasions advantage or detriment. 30. That love, then, is a kind of desire, is clear to every one; and we know that they who are not in love, desire beautiful things. How then shall we distinguish a lover from one who is not in love? Here it is necessary to observe, that in each of us there are two ruling and leading principles, which we follow wherever they lead, one being an innate desire of pleasures, the other an acquired opinion, which aims at what is most excellent. These sometimes agree in us, and sometimes are at variance; and sometimes one gets the upper hand, at other times the other. When opinion therefore with the aid of reason leads to that which is best, and gets the upper hand, we give the name of temperance to this power; but when desire drags us irrationally to pleasures and rules within us, this ruling power takes the name of excess. But excess has many names; for it has many limbs and many forms. 31. And of these principles whichever happens to get the predominance gives its own designation to the person who possesses it, and that neither honourable nor worth acquiring. For instance with respect to food, desire that gets the better of the highest reason, and of the other desires, will be called gluttony, and will cause the person who possesses it to be called by the same name; again with respect to drinking, when it has usurped dominion, by leading its possessor in this direction, it is clear what designation it will acquire: and with respect to other things akin to these, and the names of kindred desires, it is manifest how they ought to be called, according as each for the time being happens to be dominant. Why all this has been said is already pretty evident, but every thing becomes in a manner more clear by being mentioned than if not mentioned. 32. For desire without reason having got the upper hand of opinion that tends to what is right, and being driven towards the pleasure derived from beauty, and being strongly impelled by its kindred desires to corporeal beauty, receives its name from this very strength and is called love[120].