How we cite our quotes: (Book.Chapter.Bekker #s); all Bekker line numbers are approximate, since they are keyed to the original Greek.
Quote #7
For no community comes into existence out of two doctors but rather out of a doctor and a farmer and, in general, out of those who are different and not equal. But these [differing types] must be equalized. (5.5.1133a16-18)
It takes all kinds to make the world go 'round. This isn't a new thought, even in Aristotle's time. He understands that a community is something built on mutual exchange, which cannot exist without a variety of goods and services (i.e. a diversity of people) available to the citizens.
In order for this exchange to work, however, there has to be an equitable way of assessing the value of each thing to be exchanged. Aristotle tells us a little later on that the greatest equalizer of all is money. While some have more and some less, currency allows people in society to get what they need, regardless of what product they have to offer.
Quote #8
Hence all things ought to have a value assigned to them; for in this way there will always be exchange, and if there is exchange, then there will be community. Hence by making these things commensurate, money, just like a measure, equalizes them. For there is no community if there is no exchange, or exchange if there is no equality, or equality if there is no commensurability. (5.5.1133b15-18)
Aristotle defines community essentially as an economic, political unit. In this place, justice begins with exchange. Because exchange within a community makes life possible (because basic life needs must be met), there has to be equality/commensurability between the goods and services exchanged. He doesn't say it here, but Aristotle does talk about (proportional) equality between people in community as an important part of social justice as well. Here, money is the equalizer, keeping need stable. Between human beings, it's a sense of what's just for each person.
Quote #9
But it must not escape our notice that what is being sought is also the just unqualifiedly, that is, the just in the political sense. And this exists among those who share a life in common with a view to being self-sufficient, who are free and equal, either in accord with proportion or arithmetically. As a result, for all those for whom this does not exist, there is nothing politically just in relation to one another, but only something just in a certain sense and by way of a similarity. (5.6.1134a25-29)
Again, Aristotle sees justice tied to human community. But justice isn't a necessity simply because we have to be all up in each other's business: we need it especially to maintain the balance between communal living and what's necessary for an individual to thrive. Unqualified justice (or justice as a general, overarching concept) belongs to the political unit (i.e. the city, or a group of people being ruled by laws), where specific or particular justice exists to maintain equality between citizens.