From a modern perspective, “Functional finance” is really cavalier in its discussion of monetary policy. Lerner says that the interest rate should be set at the level that produces “the most desirable level of investment,” and that fiscal policy should then be chosen to achieve full employment given that interest rate. What is the optimal interest rate? He doesn’t say – maybe because through the 30s the zero lower bound made that point moot.

Anyway, what actually happens at least much of the time – although, crucially, not when we’re at the zero lower bound – is more or less the opposite: political tradeoffs determine taxes and spending, and monetary policy adjusts the interest rate to achieve full employment without inflation. Under those conditions budget deficits do crowd out private spending, because tax cuts or spending increases will lead to higher interest rates. And this means that there is no uniquely determined correct level of deficit spending; it’s a choice that depends on how you value the tradeoff.

https://www.nytimes.com/2019/02/12/opinion/whats-wrong-with-functional-finance-wonkish.html

https://www.nytimes.com/2019/02/12/opinion/how-much-does-heterodoxy-help-progressives-wonkish.html