Let us talk more about the justice that exists between citizens. Generally speaking, someone who can tell the difference between things with the same name, knows well what it means for each thing to be what it is. For instance, a breeder of dogs can tell you the names of the different breeds, and they can tell you what each is good for. So likewise here, we want to learn what each kind of justice is, that we may act as just citizens ought.

Now, there are two kinds of justice between citizens: natural and conventional. 'Conventional' means some thing is just by agreement or by law, while 'natural' means it is already just by nature, even without anyone making any rule saying so. When something is conventionally just, that means that it is so because people say it is so. But really, we can imagine that the rule could have been something else. And if it did become something else, then what was once unjust would then become just, and vice versa. So, for instance, imagine that, in one country, they play a certain sport with eleven players on each side. Well, it would be unfair (and, hence, unjust) for one team to have twelve players on the field, by the rules of that game. But we can also well imagine that there is some other country, where they have the same sport, but the rules are different, so that there are ten players to each side. So, having eleven players, on one side, which was fair before is now unfair, again, because it goes against the rules. But the rules are really no more than convention, and there is nothing in nature which says how many players there must be to each side in the sport.

Now, there are people who say that the conventional kind of justice is the one and only kind, and there is no natural justice at all. After all, what is true by nature is true everywhere. Fire burns here and it burns in Persia. But the laws are different in a different places. And if there were natural justice, then (these people say) it should be that everything (viz. all the laws) is the same everywhere, because that is what Nature makes it be (again, like how Nature makes fire burn the same in all places).

We do not agree with that argument. We think that there is such a thing as natural justice, but it is not always the same everywhere. For example, it is a general rule that people are stronger with one of their hands. That is almost always the right hand. But for specific people it is the left hand, so we have an exception to the rule. Well, it is the same with other things in nature that may be this or that generally speaking, but then for specific cases, they are different.

The fact that natural justice is not always the same, makes it seem as if there is nothing natural about it, and it is really all just convention; but that is not true. These people are looking for too much consistency, and yet the world is not that simple, and when they find the world to be too complex for their simple rules, they throw up their hands and say it is all convention. Again, they are wrong. Natural justice does exist, along with conventional justice.

And consider further the laws of hospitality. Here, I mean rules that everyone knows, but no one has made: that when a stranger calls on your household, you must first invite them in, tend to their needs, and not ask first what they want before letting them in. [This is the ancient Greek custom of xenia.] Everyone would agree that it is unjust to turn away a stranger (especially one with a similar social background), yet there is no law or convention that says this. Hospitality is something that is naturally just. It is naturally just, and, at the same time, it is also subject to change (customs can change). When the rules change, we come to hear about the changes in due time, and then we start following the new rules.

(On a side note, there is another kind of justice, which we do not cover here. This justice is unlike the natural and the conventional in that it is not subject to change. Here, I mean divine justice.)

But now, let us go more into how things differ by convention. We shall see that convention does not mean making up anything that one wishes. When people agree that there should be a convention that such-and-such is so, they are doing it with a view to some end and purpose. The reason why the convention is what it is is because the people who made it felt that it served their purposes; and that is so despite the fact that it may not be apparent to others; I mean, it seems to others like they could have made the convention be anything, when they really could not have. Also, note that, as the circumstances that the people are in vary, so also the ends and purposes may vary, and so also the conventions may vary.

You can think of the things that vary with convention like the measures used for trading things like corn or wine (i.e. bushels and barrels). The measures for corn and wine are not the same everywhere: in the places where the dealers buy wholesale they are larger, and in the places where they sell retail they are smaller. Again, it is same with anything that is said to be such-and-such by law or by common agreement: different in different places. It is the same with constitutions of different states for different countries. The countries are different and each one has a constitution which is the best one for it.

Next let us touch on how things vary by law. A law relates to the actions that go according to it as universals do to particulars. And what are universals and particulars? Whiteness, for example, is a universal, it is found in many things. Snow, is a particular white thing; a feather, may be another particular white thing. Each particular white thing has the same universal: whiteness. So likewise, we may have a law that says each person must pay a 10% property tax. That is like the universal. Then we have different people paying different amounts of taxes. That is like the particular. So, one person may pay 100 gold in tax, and that is just, because it is according to the law. Another person may pay 1000 gold in tax, and that also is just, because it also is according to the law. The point we are trying to make here is this: (1) as you can have different conventions which make justice be different (e.g. same sport, but how many players on the field is different), (2) so also you can have one and the same law, but what it means to follow that law may be different in different cases (e.g. same tax law, but each person pays a different amount).

You see, there is a difference between saying "stealing" is something that is unjust, generally speaking, and something specific being stolen (e.g. someone's wallet) is an act of injustice. This is a bit tricky, but let us see if we cannot get it right. Now, you could say that "the theft of Socrates' wallet" was an act of injustice, but you could not say that "stealing" (by itself) was an act of injustice. In order for something to be an act of injustice, there must some thing that was stolen. Likewise also, "showing respect" is just, in general, but "showing respect" is not an act of justice unless we also include someone to do it and what they do to show it. And what does this matter? It matters because what "showing respect" involves can be different among different peoples. You see, there is the category of action and the genus of just acts; there is the genus of acts showing respect, and each nation of people, has its own species of act of showing respect. (For example, as Herodotus says, of the custom of the Persians, that an inferior will kiss the cheek of a superior upon meeting.) Again, this is like the difference between the universal law (viz. that respect is to be shown) and the particulars (how it is to be shown among different peoples in different cultures).

There is more to this (viz. how the acts themselves break down into different species, and what things each species of act relates to), but we will not be going over that here.