How we cite our quotes: (Book.Chapter.Bekker #s); all Bekker line numbers are approximate, since they are keyed to the original Greek.
Quote #1
For someone who accords with the middle characteristic here is the sort of person we mean by an equitable friend, if his disposition also goes together with feeling affection for the other. This characteristic differs from friendship, however, because it is without the relevant passion, that is, the feeling of affection for those with whom one associates...(4.6.1126b21-23)
Aristotle isn't really defining friendship here. Instead, he's talking about the virtue a person might have in relation to the people around him. If this were a Jane Austen novel, we might say that this person is "amiable"—someone who knows how to be friendly in a pleasing way. This virtue is the starting point for friendship, because without it, a person would not be properly sociable.
Quote #2
In poverty as well as in other misfortunes, people suppose that friends are their only refuge. And friendship is a help to the young, in saving them from error, just as it is also to the old, with a view to the care they require and their diminished capacity for action stemming from their weakness; it is a help also to those in their prime in performing noble actions, for 'two going together' are better able to think and to act. (8.1.1155a11-16)
We can't emphasize enough how much we agree with Aristotle here: you always need your buds. There's no time of life when we can make it on our own—or if we can, it is always much more pleasant to have a companion to share in our lives. Again, Aristotle's not getting all Hallmark Channel on us here: he's totally practical. As humans, we need another set of hands, brains, and a shoulder to cry on in order to lead stable and productive lives.
Quote #3
When people are friends, they have no need of justice, but when they are just, they do need friendship in addition; and in the realm of the just things, the most just seems to be what involves friendship. Yet friendship is not only necessary but also noble, for we praise those who love their friends, and an abundance of friends is held to be a noble thing. Further, people suppose good men and their friends to be one and the same. (8.1.1155a26-31)
What exactly is it about friendship that makes justice a secondary concern? Aristotle will later posit that it's because we see our friend as a second self, and it is very nearly impossible to do an injustice to ourselves. This automatic sense of justice between friends also allows other virtues to surface, or at least makes it easier for the good side to come out.
Because of this, we always think of our friends as the "best"—kind, worthy, good people. Which is why we always ask a friend for a job recommendation, and not just anyone. And although Aristotle later tells us that we really shouldn't have many great friends, we do feel that he or she who winds up with the most friends wins.
Quote #4
Those who love each other on account of utility, then, do not love each other in themselves, but only insofar as they come to have something good from the other. Similar too is the case of those who love on account of pleasure, for people are fond of those who are witty, not because they are of a certain sort, but because they are pleasant to them. (8.3.1156a10-14)
When Aristotle speaks of love in this way, he is still speaking about friendship—or rather "friendly affection," which is a kind of passion that holds us to what is lovable in another person. This can also extend to erotic relationships, but "love" in this case is not exclusively sexual. In these types of friendships, those involved don't love their friend for who they are, but rather what they bring to the relationship. And you can imagine what happens when either friend can't deliver what's expected of him.
Quote #5
These sorts of friendships, then, are easily dissolved when the people involved do no remain the same as they were. For if they are no longer pleasant or useful, those who love them will cease to do so. And what is useful does not remain constant but is different at different times. (8.3.1156a19-22)
Aristotle is speaking here of two types of false friendships, those of utility and pleasure. These relationships are entirely practical—we would call them relationships of convenience—but are less than satisfactory in terms of emotional fulfillment. They also tend to be short-lived…for the reasons mentioned. Though this is a bleak definition of friendship, Aristotle is setting us up to understand what a strong friendship (or complete friendship) looks like.
Quote #6
But complete friendship is the friendship of those who are good and alike in point of virtue. For such people wish in similar fashion for the good things for each other insofar as they are good, and they are good in themselves. (8.3.1156b7-10)
This is ideal friendship, in which each person loves the other for his "characteristics" or virtues. Because the cause of such love resides in a part of the person that changes very little over time, the friendship has very little reason to go sour—unlike the friendships based on utility and pleasure, which are unstable because they're based on inconstant things. Also—and this will be an important part of this discussion—the friends are "good in themselves," which means that are not only lovable to others, but also to themselves.
Quote #7
Further, there is also the need of the passage of time and the habits formed by living together; for as the adage has it, it is not possible for people to know each other until they have eaten together the proverbial salt, nor is it possible, before this occurs, for them to accept each other and to be friends until each appears to each as lovable and is trusted. (8.3.1156b26-28)
This seems like a lot of work to say that someone is our friend. But Aristotle wants to make sure that we don't jump headfirst into an inferior friendship that'll end in a lot of heartache.
First requirement: friends have to spend a lot of time together. In doing so, two things happen: we become like each other (similar habits) and we learn to trust. It's also important that each person finds something stable in the other person to admire. Otherwise, we might wind up with a friendship of convenience rather than the real thing.
Quote #8
Friendship appears in each of the regimes to the extent that what is just does as well. In a king in relation to those over whom he is king, friendship consists in superiority in granting benefactions, for he benefits those over whom he is king—if in fact, being good, he cares for them so that they fare well, just as does a shepherd for his sheep. (8.11.1161a10-14)
Because friendship is intimately connected to justice, Aristotle has no problem making the leap into political relationships to see how they form under different types of rule. The king is superior of course—like the father to a son—and can't extend friendship of equality to his subjects. But in order to keep monarchy in line (i.e. away from tyranny) there has to exist some of the same affection that we have in friendships to keep the balance of power on the right side of justice.
Quote #9
The friendship of a husband for a wife is the same as that in aristocracy, for it accords with virtue, and to the better person goes more of the good and to each what is suited to each. So also in the case of what is just. The friendship of brothers is like that of comrades...also resembling this friendship is the friendship pertaining to timocracy, for the citizens wish to be equals and equitable. (8.11.1161a23-27)
Aristotle continues to map the concept of intimate friendships onto political life in order to see how these relationships work on the macrocosmic levels. What we see happening in households can be seen in society at large, as is the case in the friendship between husband and wife and brothers.
There's no equality in marital friendship (hey, it's ancient Greece), but there is a kind of kindred nobility there, and a sense that each partner merits their own things. Brothers are the closest to total equality, like a timocracy—a polity governed by those who pay property taxes.
Quote #10
...but human beings live together not only for the sake of begetting children but also for the sake of the things that contribute to life, for the tasks involved are divided immediately, those of the husband being different from those of the wife. They assist each other, then, by putting their own things in the service of what is common. For these reasons, both what is useful and what is pleasant seem to be found in this friendship... (8.12.1162a21-24)
Okay, we know this is not the most romantic definition of marriage, but we think that Aristotle has really hit on something in his description of marital friendship. The family home here has become a kind of self-sufficient commune, and husband and wife equal not in their capacities, but in their ability to contribute to the household. Aristotle understands that helping each other could be just about the sexiest thing that spouses can do for each other. Or perhaps that's just our reading...