Thesis: As with desert, and justice more generally, reciprocity is a cluster concept.

RECIPROCITY'S CANONICAL FORM

Reciprocity in its canonical form applies to relations among autonomous adults, not to our dealings with those who are helpless. Crucially, if reciprocity pertains to the question of how to be a proper recipient, it will say nothing about what we owe to people who cannot do their share, because reciprocity concerns what we owe to people who have already done their share. With regard to people who did not (and perhaps cannot) do anything to put us in their debt, reciprocity does not tell us what to do. It does not tell us why. More generally, it says little about when or how or why to make the first move, because reciprocity primarily is about how to respond when someone else has made the first move.

We enter reciprocity's domain when we ask how to respond to people who have done us a favor. If that is not the question, then reciprocity is not the answer.

TRANSITIVE RECIPROCITY

Or at least, reciprocity in its canonical form is not the answer. There are variations on the theme, though, that speak to broader questions about moral obligation. Reciprocity in its canonical form obliges us to return favors specifically to our original benefactors. I refer to this form of reciprocity as symmetrical reciprocity.