Virtue that wavers is not virtue, but vice revolted from itself, and after a while returning. The actions of just and pious men do not darken in their middle course.
Our virtues are voluntary (and in fact we are in a sense ourselves partly the cause of our moral dispositions, and it is our having a certain character that makes us set up an end of a certain kind), it follows that our vices are voluntary also; they are voluntary in the same manner as our virtues.