Robert Waldmann on the deep rifts between the two major schools of thought in modern macroeconomics that have been brought to the fore again by the current economic crisis:
In the field of macroeconomics there is a much deeper division between macroeconomics as practiced at universities closer to the great lakes than to an Ocean (Fresh water economics) and that practiced at universities closer to Oceans (Salt water economics). The geography has shifted some as Fresh water economics has been exported. I’d consider Professor Robert Barro at Harvard to be brackish (with, he reports, noticed salty contamination in the first 6 months after he moved from U. Rochester) and the economics department at the University of Pompeu Fabra (in Barcelona) seems to be distilled. It is a little difficult to explain the disagreement to non economists. Frankly, I think this is because non-economists have difficulty believing that any sane person would take fresh water economics seriously.
Roughly Fresh water economists consider general equilibrium models with complete markets and symmetric information to be decent approximations to reality. Unless they are specifically studying bounded rationality they assume rational expectations, that everyone knows and has always known every conceivable conditional probability. I’ve only met one economists who claims to believe that people actually do have rational expectations (and I suspect he was joking). However, the fresh water view is that it usually must be assumed that people have rational expectations.
Salt water macroeconomics is basically everything else with huge differences between people who attempt to conduct useful empirical research without using formal economic theory and people who note the fundamental theoretical importance of incomplete markets and of asymmetric information and of imperfect competition (as in everything you think you know about general equilibrium theory is known to be false if markets are incomplete or there is asymmetric information or there is imperfect competition – Market outcomes are generically constrained Pareto inefficient which means that everyone can be made better off by regulations imposed by regulators who don’t know anything not known to market participants who also just restrict economic activity and don’t introduce innovations like, say, unemployment insurance).
Leading fresh water macroeconomists include Robert Lucas, Ed Prescott Thomas Sargent, Lars Hansen, John Cochrane, Larry Jones, Robert Barro (mostly), and Kevin Murphy (usually). Leading salt water economists include Paul Samuelson, Edmund Malinvaud, Jacques Dreze, Joseph Stiglitz, Robert Solow, Paul Krugman, Andrei Shliefer, Olivier Blanchard, George Akerlof, Robert Hall, Ben Bernankle, N. Gregory Mankiw, Christina Romer, David Romer and, and Lawrence Summers. Brad DeLong is also a salt water economist and he is very very smart, but last I knew, he was a little too far out there to be really a member of the economists club. I can’t classify Paul Romer.