Moral Letters to Lucilius Section 9

Ad haec respondeo: et qui in summo est calore, opus est calore adiecto, ut summum teneat. Sed ipse se, inquit, calor continet. Primum multum interest inter ista, quae comparas; calor enim unus est, prodesse varium est. Deinde calor non adiuvatur adiectione caloris, ut caleat; sapiens non potest in habitu mentis suae stare, nisi amicos aliquos similes sui admisit, cum quibus virtutes suas communicet.

les corps mêmes pénétrés d’une extrême chaleur ont besoin d’une chaleur additionnelle pour se maintenir à ce point extrême. « Mais la chaleur se maintient par elle-même. » D’abord il y a peu d’analogie entre tes termes de comparaison. La chaleur est une, l’utilité est diverse. Ensuite la chaleur, pour être chaleur, ne demande pas qu’on y ajoute ; mais le sage ne peut demeurer dans son état de perfection, s’il n’adopte quelques amis qui lui ressemblent, pour faire avec eux échange de vertus.

My answer to this is, that when one is heated to the highest degree, one must have continued heat to maintain the highest temperature. And if it be objected that heat is self-maintaining, I say that there are great distinctions among the things that you are comparing; for heat is a single thing, but helpfulness is of many kinds. Again, heat is not helped by the addition of further heat, in order to be hot; but the wise man cannot maintain his mental standard without intercourse with friends of his own kind - with whom he may share his goodness.