Moral Letters to Lucilius Section 22

Si hanc opinionem receperis, aliquid bonum esse praeter honestum, nulla non virtus laborabit. Nulla enim optineri poterit, si quicquam extra se respexerit. Quod si est, rationi repugnat, ex qua virtutes sunt, et veritati, quae sine ratione non est. Quaecumque autem opinio veritati repugnat, falsa est.

Si tu admets l’opinion qu’il est encore d’autre bien que l’honnête, plus de vertu qui n’en soit ébranlée ; pas une en effet qui se puisse maintenir, si elle aspire, en dehors d’elle-même, à quoi que ce soit. Cet état de choses répugne à la raison, de laquelle les vertus procèdent, à la vérité, qui n’existe point sans la raison ; et toute opinion qui répugne à la vérité est fausse.

If, however, you accept the view that there is anything good besides that which is honourable, all the virtues will suffer. For it will never be possible for any virtue to be won and held, if there is anything outside itself which virtue must take into consideration. If there is any such thing, then it is at variance with reason, from which the virtues spring, and with truth also, which cannot exist without reason. Any opinion, however, which is at variance with truth, is wrong.