… is from pages 460-461 of my late colleague Jim Buchanan ‘s 1986 Nobel Prize lecture, “The Constitution of Economic Policy ,” as it is reprinted in volume 1 of The Collected Works of James M. Buchanan: The Logical Foundations of Constitutional Liberty  (original emphasis):
Individuals choose, and as they do so, identifiable economic interest is one of the “goods” that they value positively, whether behavior takes place in markets or in politics. But markets are institutions of exchange; persons enter markets to exchange one thing for another. They do not enter markets to further some supra-exchange or supra-individualistic result. Markets are not motivationally functional; there is no conscious sense on the part of individual choosers that some preferred aggregate outcome, some overall “allocation” or “distribution” will emerge from the process.
The extension of this exchange conceptualization to politics counters the classical prejudice that persons participate in politics through some common search for the good, the true, and the beautiful, with these ideals being defined independently of the values of the participants as these might or might not be expressed by behavior.