|David Levine's analogy for Stimulus|
David does a lot without equations. That broadens the appeal, but equations can be useful. For example equations clarify that crucial difference between budget constraints and equilibrium conditions. Equations can put to rest silly controversies. We might not still be writing papers, books, and blog posts about what "Keynes really meant," 80 years after the fact, or using "Say's law" as rotten tomatoes, if Keynes had written some equations. Cynically, maybe the lesson is that lack of equations -- or even an equations appendix or citation -- keeps debate going and your name in the papers.
I also fear that his lovely anecdote about people each of whom wants what others produce will lead readers a bit astray. Keynesian economics is about lack of "demand," sticky prices not absent prices. It's not about absence of money, double coincidence of wants, and so forth.
David goes beyond the usual IS/LM formalism, to explain some of the "coordination failure" interpretations of Keynes. He also references Axel Leijonhufvud's "great and famous work" describing a mismatch between saving, a desire for generic future consumption, and the demand for specific goods that firms need to invest.
He has a nice personal story of his Keynesian upbringing, which reminds me of my own. And
Knowledge of Keynesianism and Keynesian models is even deeper for the great Nobel Prize winners who pioneered modern macroeconomics - a macroeconomics with people who buy and sell things, who save and invest - Robert Lucas, Edward Prescott, and Thomas Sargent among others. They also grew up with Keynesian theory as orthodoxy - more so than I. And we rejected Keynesianism because it doesn't work not because of some aesthetic sense that the theory is insufficiently elegant.The constant refrain that critics "don't know" Keynesian economics is an ingorant (I mean that not an insult, but in its literal meaning, ignoring the facts) calumny. Sargent's first book "Macroeconomic Theory" is a great example of a modern economists wrestling hard with Keynes.
The last paragraph is a gem:
Keynes own work consists of amusing anecdotes and misleading stories. Keynesianism as argued by people such as Paul Krugman and Brad DeLong is a theory without people either rational or irrational, a theory of graphs pulled largely out of thin air, a series of predictions that are hopelessly wrong - together with the vain hope that they can be put right if only the curves in the graphs can be twisted in the right direction. As it happens we have developed much better theories - theories that do explain many facts, theories that provide sensible policy guidance, theories that work reasonably well, theories that are not an illusion. The current versions of these theories are very unlike caricature theories of hopelessly rational people who are all identical. Current theories are not perfect - but unlike the Keynesian theory of perpetual motion machines they explain a great deal and have a great deal of truth to them. A working macroeconomist reading Krugman and DeLong feels as a doctor would if the Surgeon General got up and said that the way to cure cancer was to draw blood using leeches.