In his provocative book, How Judges Think (2008), Judge Richard A. Posner highlights the economically remarkable fact that federal judges who take senior status -- under which they continue to judge, though with a reduced load, while still earning full salary -- are in effect "working for nothing" (61) , since they could also have retired completely from judging and still kept the same full salary. (A nice deal.)
He hastens to remind us that the senior status judges' choice "is consistent with rational behavior." (61 n.7) So it is, if we posit, as Posner does, that the judges have "a taste for being a good judge." (60) If judges have this taste, then satisfying it delivers value to them; hence their decision to work for nothing is actually a decision to work for something, namely the satisfaction of this taste, a reward they could not get if they retired from judging altogether.
This argument is perfectly coherent. But it has a striking feature, which no doubt is old news to critics of law & economics: it makes the economic theory of rational behavior unfalsifiable. Since every choice can be described as satisfying the chooser's taste for making that choice, every choice must satisfy the criterion of rationality that it advance the chooser's ends. If that criterion is too loose, and we insist instead that the choice must advance some end more abstract than the end of making that very choice, we can certainly find cases where people's choices are ill-calculated to achieve their own more abstract ends (and finding and explaining such cases of unsuccessful self-interested behavior is an important field of current study, in particular in "behavioral economics"). But we still cannot falsify the proposition that all behavior aims to be self-interested, because even the most altruistic act can be described as satisfying the actor's taste for altruism.
That's okay, in a sense. It doesn't necessarily matter whether people act altruistically out of a sense of obligation or out of desire for the taste of altruism. In fact, the "taste" may even have a neurochemical basis; at least, that's what the public radio fundraiser said the other day, explaining that acts of giving result in the release of a pleasurable hormone in the giver's brain. So if we think that altruistic acts are desirable (and whether the reason we think that is hormonal or philosophical), we simply need to encourage people to develop the taste and to structure social situations in which that taste can be satisfied.
Still, if we are interested in understanding the sources of altruistic behavior, the "taste" theory is essentially opaque. It is not self-evident that the taste for altruistic behavior is the same kind of taste, with the same kind of chemical or cognitive or emotional basis, as the taste for economic gain. It may not be easy to imagine a situation in which someone with a taste for the pleasure of altruism would act differently than someone who recognized the moral obligation to be altruistic, but these two people may not be the same. We may before too long be able to trace the pathways of thought and feeling with enough precision to see whether acts experienced as flowing from moral obligation are distinguishable, in terms of mental processes, from acts experienced as efforts to satisfy self-interest. Many of us have the intuition that some people really are less selfish than others; neurobiology may yet prove this intuition right.