Leaving aside the various forms and definitions of justice, about which many authors have written in their sundry ways, it is our intention in this prologue to limit ourselves to considering that particular justice which is the very basis of royal power, in that it punishes evildoers and allows good people to live in peace. In doing this we shall not pretend to create or devise new theories of our own; rather, we shall assemble from certain authors a handful of those views that have appealed to us. Our first aim is to guide our audience into understanding what our narrative is about; our second aim is to follow precisely the order set out in our first prologue.

King Pedro, whose reign we shall now describe, meted out justice, and, as the saints have written, to dispense justice is more pleasing to God than any other worthy action that a monarch can perform. Moreover, since some people wish to know what that virtue consists of and to what extent such virtue, which must be found in a king, is also appropriate in his people, you will now be able to read about it in the straightforward style that corresponds to our understanding of it.

Justice is a virtue which is recognized as embracing all virtues, in the sense that any person who is just is entirely virtuous, because justice, being God's law, forbids fornication and gluttony, and in its observance we uphold the virtues of chastity and temperance. The same applies also to the other vices and virtues.

This virtue is essential to a king and, indeed, to his subjects, because if the king possesses the virtue of justice he will enact laws so that all should live lawfully and in peace, and his subjects, themselves also just, will observe the laws that he enacts and in their observance will commit no wrong against anyone. Such justice as this can be acquired by anyone of sound judgement. In some instances people are born with a natural sense of justice and enthusiastically put it into practice, even if they are prone to certain vices.

The reason why this virtue is necessary to the prince's subjects is that it causes them to observe his laws, which should always be framed for the public good.