Reciprocity—put most generally—is the idea of actions-in-return that are not founded in voluntary agreements or contracts. Understood in this way, reciprocity can be one-on-one: the return of a kindness or the exchange of presents. But it need not be: pitching in to do one’s share of cooking for a potluck supper, cleaning up the local park, or contributing to the local public radio station. Here, the idea of reciprocity is doing one’s part to produce a common good, when—and especially because— others are doing theirs.
The moral contribution of reciprocity in such cases is that pitching in rests not only on the idea of fair shares coupled with the recognition that the desired outcome will not be produced if too many fail to contribute, but also on the fact that others are doing their part. Free riders fail to do their fair shares, but this is not the full moral story. In addition, free riders let others down by failing to respond in return to the good efforts that others are making.