No one has laid down the principle more emphatically than Seneca himself.  Take, for instance, the following passage from his Letters, on evil conversation.  “The conversation,” he says, “of these men is very injurious; for, even if it does no immediate harm, it leaves its seeds in the mind, and follows us even when we have gone from the speakers,—­a plague sure to spring up in future resurrection.  Just as those who have heard a symphony carry in their ears the tune and sweetness of the song which entangles their thoughts, and does not suffer them to give their whole energy to serious matters; so the conversation of flatterers and of those who praise evil things, lingers longer in the mind than the time of hearing it.  Nor is it easy to shake out of the soul a sweet sound; it pursues us, and lingers with us, and at perpetual intervals recurs.  Our ears therefore must be closed to evil words, and that to the very first we hear.  For when they have once begun and been admitted, they acquire more and more audacity;” and so he adds a little afterwards, “our days flow on, and irreparable life passes beyond our reach.”  Yet he who wrote these noble words was not only a flatterer to his imperial pupil, but is charged with having deliberately encouraged him in a foolish passion for a freedwoman named Acte, into which Nero fell.  It was of course his duty to recall the wavering affections of the youthful Emperor to his betrothed Octavia, the daughter of Claudius, to whom he had been bound by every tie of honour and affection, and his union with whom gave some shadow of greater legitimacy to his practical usurpation.  But princes rarely love the wives to whom they owe any part of their elevation.  Henry VII. treated Elizabeth of York with many slights.  The union of William III. with Mary was overshadowed by her superior claim to the royal power; and Nero from the first regarded with aversion, which ended in assassination, the poor young orphan girl who recalled to the popular memory his slender pretensions to hereditary empire, and whom he regarded as a possible rival, if her cowed and plastic nature should ever become a tool in the hands of more powerful intriguers.  But we do not hear of any attempt on Seneca’s part to urge upon Nero the fulfillment of this high duty, and we find him sinking into the degraded position of an accomplice with young profligates like Otho, as the confident of a dishonourable love.  Such conduct, which would have done discredit to a mere courtier, was to a Stoic disgraceful.  But the principle which led to it is the very principle to which we have been pointing,—­the principle of moral compromise, the principle of permitting and encouraging what is evil in the vain hope of thereby preventing what is worse.  It is hardly strange that Seneca should have erred in this way, for compromise was the character of his entire life.  He appears to have set before himself the wholly impossible task of being both a genuine philosopher and a statesman under the Caesars.  He prided himself on being not only a philosopher, but also a man of the world, and the consequence was, that in both capacities he failed.  It was as true in Paganism as it is in Christianity, that a man must make his choice between duty and interest—­between the service of Mammon and the service of God.  No man ever gained anything but contempt and ruin by incessantly halting between two opinions.