Some time ago—well over a year—some friends and I had been to lunch in the campus cafeteria and were returning to our building. One friend held the door for us as we went in. I went up to my office and settled into the afternoon’s work. Half an hour later I discovered the friend had sneaked home after holding that door for us, and found myself—let’s call it—slightly miffed because he’d left without saying goodbye. Not a big deal, really. I teased him about it and he apologized and we were good to go.
It was a very little thing. Even at the time I said to him that my mildly ruffled feathers didn’t seem fair because I had no particular claim to a goodbye, and my disappointment seemed out of proportion to the situation.
But it does make me wonder: What was going on there? Was my emotional response unfair or out of proportion? Do friends “owe” one another things like a quick goodbye when they’re leaving, particularly at an unusual time? I don’t go out of my way to say goodbye to every colleague on my floor when I’m leaving for the day, but I do say it to the nearby ones. It feels weird to me not to.
These little questions have gotten me thinking more generally: What do we owe to friends in virtue of the friendship?

Friendship is hard to say anything general about, because there are so many different kinds of friends and depths of friendship.
Philosophical literature on friendship, from what I can tell from a short research foray, seems to discuss the obligations of friendship relative to our more general moral obligations, mostly asking how our “special obligations” to our friends fit into the map of ethics writ large. But what I’m interested in here is what it’s really fair to expect of friends when larger morality isn’t an issue—the internal structure of friendship, if you will.
I haven’t found anything on this, other than a little that says that we can’t say much about what we owe to friends because friendships can be so different. It’s true that friendships are kind of nebulous. We don’t sit down and define them, most of the time. And we don’t have formal mechanisms for breaking up or changing them. Also, we say we choose our friends, but often, we just fall into them—we find ourselves to be friends. So it’s really hard to define what to expect within a relationship of friendship because you never have the conversations that define what kind of friends you are. For all these reasons, what you “owe” to one friend you might not “owe” to another because you have different relationships with them.
There’s a view that the so-called obligations of friendship are supposed to be undertaken voluntarily. There are two aspects to this. One is that any obligations you have as a friend are like promises: you obligate yourself by making them. The other is that if you’re helping friends out of duty rather than because you care about them, the help seems lesser. Friends are supposed to be motivated by their love for one another—which seems to be a thing that’s meant to come from them, and not something you get to ask of them. In that case, what do we say when they fail to act out of love in such a way? Have they done us any sort of wrong? Is it fair for us to feel upset in any way?
The issue seems to hinge on the difference between what you can expect of someone descriptively—as in, the regular patterns of interaction you can as a matter of fact rely on—and what you can expect of them prescriptively (or normatively, in philosophy-speak)—what you can ask of them and think they’re in the wrong if they don’t do.
On the voluntary model of friendship,1 then, you can (descriptively) expect a friend to do certain things because there’s a pattern of behavior you’ve come to rely on within the friendship. But if friendly behavior is meant to be voluntary, then the question at hand amounts to whether you should expect that behavior in the normative sense—the sense in which you get to be upset if they don’t do it.2
Even if the answer to that question is no, that doesn’t mean you never have a “right” to ask friends for favors that you wouldn’t ask of a stranger. It’s common to call on a friend when you need someone to be your “plus one” at an event or to help you move, or when you need to crash on a couch. That seems perfectly reasonable. I take it the general understanding is that they don’t have to say yes when you ask something big(ish) of them—you do have to ask—but they should give your request special consideration. So it seems like they don’t have an obligation to grant you any given favor. But my own intuitions say that they probably do owe you a reason why they’re not helping out.3
How would the logic of this go? I love you, and in light of that, I’m supposed to think about you and take you into account in various ways, given that we’re friends. I’m supposed to value your interests and well-being in a special way, and further them to the extent I can (within reason). Love (in my view) requires, and characteristically motivates, that I do the things that protect and enhance who you are—particularly who you are to me, as a friend. And I’m supposed to do (many of) the things you reasonably expect of me, both normatively and descriptively, and if I don’t, I probably owe you some sort of explanation at least. I think love calls for this because if it ties your interests and mine together, then we should—normative “should”—be acting out of consideration for one another (in appropriate circumstances, within the parameters of what sort of friends we are, how close, etc.).
All of this suggests that my little miffed reaction to the friend who held the door and then disappeared was a not-unreasonable response to the (descriptive) expectation that he would say goodbye when he left, because that was the pattern I was used to. And in light of this pattern, probably he (normatively) should have thought that I’d be thrown off by his leaving without saying anything. Knowing that, in turn, he (normatively) should have been motivated by his care for me to at least send a quick message saying that he was escaping for the day.
That’s the logical analysis of the situation, anyway. It makes sense of my reaction, though that wasn’t itself a product of logic.
So what have we got? In short, you don’t have to be my friend, but if you are, then you should do XYZ, where the details of XYZ will vary depending on our relationship, but will be in the neighborhood of responding to my needs and interests out of care.4 Of course, that doesn’t provide a lot of guidance unless you have a good sense of what XYZ are for any particular friendship. But it’s something.
As I mentioned, I’m not 100% sure that friendships are as voluntary as philosophy on this seems to think. But that’s another story, and the voluntary model has plenty going for it—not least of which is the fact that even if you “find yourself” to be friends with someone because of circumstances, whether you remain friends after the initial conditions fade away is plausibly a matter of choice.
To be clear, I know in my own case I’m sometimes upset when it isn’t fair for me to be. Emotions don’t always match our rational assessment of a situation. The question I want to ask is when (if ever) it is appropriate to be upset in some way—angry, disappointed, hurt, etc.
If I’m right about this, it’s probably because the expectations/obligations of friendship are in part expressive of care, and when you’re not following through on what would normally be expected of you, giving a reason is a way of expressing care that can substitute for the action you’re not doing.
(Conversely, if you habitually fail to do XYZ, then it seems you’re not my friend after all, or maybe you’re a different kind of friend than I thought.)