So I liked this post by Matthew Yglesias, where he invokes Kuhn and draws an analogy between macroeconomics and the Copernican revolution in astronomy. He recounts how Copernican (Earth revolves around the sun) astronomy eventually supplanted Ptolemaic (Earth is center of universe), but initially the Ptolemaic system made much better predictions, and concludes:
My view, with both all due respect and all due derision, is that the Robert Lucas types are like the early Copernicans here. There’s something admirable in their insistence that it ought to all work out to an easily modeled system grounded in compelling theoretically considerations. The New Keynesian model is a mess, like late-Ptolemaic astronomy, thrown together to account for observed reality. But you don’t fly to a moon with an elegant model that delivers mistaken predictions about where the moon’s going to be. And what we actually need is a Kepler to give us an elegant model that actually predicts the phenomena, and then a Newton who can explain what that model means.Hmmm... I'm more inclined to place the users of old Keynesian models, including the IS-LM-based macroeconometric models used by policymakers, in the "late-Ptolemaic" role, but, in any case, the Kuhninan approach helps explain why I simultaneously agree with Brad DeLong, Paul Krugman and Greg Mankiw that the IS-LM model remains a very useful tool, while being a little more optimistic than Krugman about the state of macroeconomics.
Also, I'm not sure that Lucas and others (including new Nobel laureate Tom Sargent) who have pushed macroeconomics towards "structural" or "micro-founded" models are leading us to an "easily modeled system." What counts for "elegance" in modern macro is consistency between the macroeconomic model and micro-economically optimal behavior on the part of consumers and firms (I suppose the obvious retort to that is to invoke Emerson: "A foolish consistency is the hobgoblin of little minds").