Causality and the new World Economic Outlook (WEO)

I often say that causality is the main, but not the only, difference between mainstream and heterodox approaches in macroeconomics. It's true for differences between Say's Law versus the Principle of Effective Demand, for discussions of exogenous/endogenous money, and also for interpretations of the relation between growth and productivity.

The new WEO is out (here). This one the first under Maurice Obstfeld, who substituted Oliver Blanchard. The explanation for lower growth in Obstfeld's intro says the following:

What underpins forecasts of moderating growth? First, the ongoing experience of slow productivity growth suggests that long-run potential output growth may have fallen broadly across economies. Persistently low investment helps explain limited labor productivity and wage gains, although the joint productivity of all factors of production, not just labor, has also been slow.*

So low productivity growth causes low output and employment growth, rather than vice versa. Further, lower investment is what causes low labor productivity, which is actually a plausible mechanism. No new machines, no increase in labor productivity.

But as the IMF has recently noticed, the accelerator is the mechanism that explains investment behavior (see here on the previous WEO rediscovery of the accelerator, and also Obstfeld says in the following line: "low aggregate demand... discourages investment"), and that implies that growth is what determines investment and, as a result, labor productivity. So low growth is caused by low growth. Good job!

* I'll leave out the problems with total factor productivity, which have been extensively discussed in the blog before.