Suppose somebody says something like “Well, government borrowing drives up interest rates, and higher interest rates depress private investment, so increasing government spending in a slump is actually contractionary.” People who try to do economics without any kind of mathematical modeling do indeed say things like that — and it’s very hard to explain why it’s self-contradictory nonsense without a bit of math.

Oh, and my sense is that it really was macro — and specifically Keynesian macro — that made economics the model-oriented field it has become. Keynes was a pretty klutzy modeler; yet even so, his little equilibrium story about a depressed economy in Chapter 3 (which Samelson later clarified into the famous 45-degree diagram) gave you more insight into what is going on in depressions than weeks spent swimming through the murk of, say, Haberler’s Prosperity and Depression.

All that said, yes, there’s a lot of excessive and/or misused math in economics; plus the habit of thinking only in terms of what you can model creates blind spots. I gave a set of lectures about that.

…

So yes, let’s critique the excessive math, and fight the tendency to equate hard math with quality. But in the course of various projects, I’ve seen quite a lot of what economics without math and models looks like — and it’s not good.

Vir: Paul Krugman, New York Times