To continue with the thoughts I was discussing last week under this heading:
Under the view I'm discussing, a variety of prescriptive legal theories have "worked themselves impure" in the words of Kessler and Pozen. These theories have begun as a purist account of how the law ought to work given one central idea. But they then have encountered difficult facts, contending interpretations, etc. and have gradually incorporated impurities, until it becomes clear that they weren't the revolution or New Paradigm they were first sold as.
An example, cost-benefit analysis. In the incarnation that concerns the authors of this life-cycle view, CBA got a bold start in the early 1980s, but encountered difficulties before the end of that decade, in part because of an atmosphere of scandal that came to surround some of the administrative offices that had to take the point on this march.
Also, on the academic front, CBA came under criticism for being a mere pretext for a political push to deregulate for the sake of deregulation. Robert Percival would write in 1991 that the program focused "almost exclusively on reducing costs to industry."
The Clinton administration (the "first Clinton administration," as history will eventually record it) gave a bipartisan cast to CBA by announcing its own initiatives under that name in 1993. Yet the theory was by this time considerably more "impure" than it had been and became more so through the next turn of the partisan cycle -- another Bush, and Obama. People began to talk about weighing "qualitative" as well as "quantitative" elements as costs and as benefits.
Over time, by the lights of people such as Judge Posner who had advocated the earlier purer sort of CBA, this was no longer CBA at all. The whole point was to treat both sides as quantitative. Otherwise, the whole concept of the balance between them seems senseless.
Such then is the life cycle.