And I know too very well that Critias and Alcibiades lived very virtuously as long as they frequented him; not that they were afraid of him, but because they thought it most conducive to their designs to live so at that time.
Many who pretend to philosophy will here object, that a virtuous person is always virtuous, and that when a man has once come to be good and temperate, he will never afterwards become wicked nor dissolute; because habitudes that can be acquired, when once they are so, can never more be effaced from the mind.

But I am not of this opinion; for as they who use no bodily exercises are awkward and unwieldy in the actions of the body, so they who exercise not their minds are incapable of the noble actions of the mind, and have not courage enough to undertake anything worthy of praise, nor command enough over themselves to abstain from things that are forbid.

For this reason, parents, though they be well enough assured of the good natural disposition of their children, fail not to forbid them the conversation of the vicious, because it is the ruin of worthy dispositions, whereas the conversation of good men is a continual meditation of virtue.

Thus a poet says, "By those whom we frequent, we're ever led: Example is a law by all obeyed.
Thus with the good, we are to good inclined, But vicious company corrupts the mind." And another in like manner: "Virtue and vice in the same man are found, And now they gain, and now they lose their ground." And, in my opinion, they are in the right: for when I consider that they who have learned verses by heart forget them unless they repeat them often, so I believe that they who neglect the reasonings of philosophers, insensibly lose the remembrance of them; and when they have let these excellent notions slip out of their minds, they at the same time lose the idea of the things that supported in the soul the love of temperance; and, having forgot those things, what wonder is it if at length they forget temperance likewise?
I observe, besides, that men who abandon themselves to the debauches of wine or women find it more difficult to apply themselves to things that are profitable, and to abstain from what is hurtful.

For many who live frugally before they fall in love become prodigal when that passion gets the mastery over them; insomuch that after having wasted their estates, they are reduced to gain their bread by methods they would have been ashamed of before.