This month marks the 50th anniversary of Milton Friedman's
The Role of Monetary Policy, one of the most influential essays in economics ever. To this day, economics students are well advised to go read this classic article, and carefully. The
Journal of Economic Perspectives hosted three excellent articles, by Greg Mankiw and Ricardo Reis, by Olivier Blanchard, and by Bob Hall and Tom Sargent.
Friedman might have subtitled it "neutrality and non-neutrality." Monetary policy is neutral in the long run -- inflation becomes disconnected from anything real including output, employment, interest rates, and relative prices. But monetary policy is not neutral in the short run.
There are three big ingredients of the macroeconomic revolution of the 1960s and 1970s. 1) The remarkable neutrality theorems including the Modigliani Miller theorem (debt vs. equity does not alter the value of the firm), Ricardian equivalence (Barro, debt vs. taxes doesn't change stimulus), and the neutrality of money. 2) The economy operates intertemporally, not each moment in time on its own. 3) Basing macroeconomics in decisions by people, not abstract relationships among aggregates, such as the "consumption function" relating consumption to income. Efficient markets, rational expectations, real business cycles, etc. integrate these ingredients. You can see all three underlying this article.
As money is not neutral in the short run, the neutrality theorems are not true of the world in their raw form, but they form the supply and demand framework on which we must add frictions. Friedman's permanent income hypothesis really kicked off the latter, and The Role of Monetary Policy is a central part of the first.
I. The Phillips curve
Friedman's view on the Phillips curve is the most durable and justly famous contribution. William Phillips had observed that inflation and unemployment were negatively correlated. (The observation is often stated in terms of wage inflation, or in terms of the gap between actual and potential output.)
For fun, I plotted the relationship between inflation and unemployment in data up until 1968, with emphasis in red on the then most recent data, 1960-1968. This was the evidence available at the time.
The Keynesians of Friedman's day had integrated this idea into their thinking, and advocated that the US exploit the tradeoff to obtain lower unemployment by adopting slightly higher inflation.
Friedman said no. And, interestingly for an economist whose reputation is as a dedicated empiricist, his argument was largely theoretical. But it was brilliant, and simple.