commands categorically; not, therefore, by the empirical knowledge that we have of men as they are, but by the rational knowledge how, according to the ideas of humanity, they ought to be. These three maxims of the scientific treatment of ethics are opposed to the older apophthegms:

1. There is only one virtue and only one vice.

2. Virtue is the observance of the mean path between two opposite vices.

3. Virtue (like prudence) must be learned from experience.