That’s the thing about MMT. To the extent it prescribes a sustainable monetary policy — that is, a low inflation rate voters will accept — it’s not new.

MMT is “new” in the sense that it removes the observed rate of growth and the debt/GDP ratio as policy-making inputs, replacing them with the guesstimated size of the negative output gap, which can be large even if the economy is growing. That replacement is hard to accomplish because it requires a reason compelling enough to overcome the difficulty of sizing the output gap. But that issue does not go to the newness, or at least the emergent relevance, of MMT in a time of zero-marginal cost production, globalization and robotics.

In simple terms, we have learned how to make things more rapidly than we can absorb them. MMT is part of the solution to that problem.