To Florus 5.61

Will, then, which is nothing other than a movement of the mind under no compulsion, owes its possibility to nature and its result to itself. It arose within nature, but from possibility, not necessity. If someone says here, ‘But a nature capable of an evil will is evil,’ I answer, ‘But a nature capable of a good will is good.’ It would therefore be called excellent and utterly evil at the same time. Yet the nature of things does not permit one and the same thing at one and the same time to be filled with opposing moral qualities. If it is thought evil because it could do evil, let it be believed good because it could do good. ‘Why,’ he asks, ‘could the nature that did good also do evil?’ I answer: because this good called virtue could not belong to the person as his own unless it were voluntary. It would not be voluntary if it carried the necessity of good; it would have suffered the necessity of good if it had not possessed the possibility of evil. Therefore, to preserve the right of good, the possibility of evil was admitted.