I call that law universal, which is conformable merely to dictates of nature; for there does exist naturally an universal sense of right and wrong, which, in a certain degree, all intuitively divine, even should no intercourse with each other, nor any compact have existed.
Every art and every inquiry, and similarly every action and choice, is thought to aim at some good; and for this reason the good has rightly been declared to be that at which all things aim.
The goodness or badness, justice or injustice, of laws varies of necessity with the constitution of states. This, however, is clear, that the laws must be adapted to the constitutions. But if so, true forms of government will of necessity have just laws, and perverted forms of government will have unjust laws.
But the virtues we get by first exercising them, as also happens in the case of the arts as well. For the things we have to learn before we can do them, we learn by doing them, e.g. men become builders by building and lyre players by playing the lyre; so too we become just by doing just acts, temperate by doing temperate acts, brave by doing brave acts.