Modern Monetary Theory has been revolutionary in economics, and its influence is — beneficially — ever-more pervasive. It has opened the eyes of a generation to a clear-eyed, accounting-based methodology that trumps dimensionless theory, and has brought a deep, nuts-and-bolts understanding of money, debt, and financial institutions to a discipline where that understanding has been inexcusably absent. Witness: a whole raft of papers from central-bank economists worldwide embracing MMT principles (though often not MMT by name), and eviscerating decades or centuries of facile and false explanations of monetary mechanisms.

But MMT's terminology and associated accounting constructs remain problematic and contentious, even among some MMT supporters like the splinter group, the Modern Monetary Realists. Some of this contention results from the usual resistance to new ideas and ways of thinking. But some arises, in my opinion, because MMT terms and accounting constructs are indeed problematic. (The terminological confusion even causes some to object correctly, but for the wrong reasons – and vice versa!)

These difficulties are apparent when you consider one of MMT's central and oft-repeated mantras and accounting identities, here in its simplified form for a closed economy ignoring Rest of World, courtesy of the redoubtable Stephanie Kelton:

Domestic Private Surplus = Government Deficit

This suggests an important truth, as far as it goes: public (monetarily sovereign federal government) deficit spending creates private assets out of thin air. The government spends new money, created ab nihilo, into private accounts. +Private Assets. No change to private liabilities. So: +Private Sector Net Worth.

But it doesn't actually go very far. That “private surplus” (a term that is absent from the national accounts, and from MMT's ur-text, Monetary Economics by Godley and Lavoie) is not defined in accounting terms, except circularly and tautologically: it's the amount that private assets increase as a result of government deficit spending. That makes the identity true by definitional tautology.

But contrary to what's at least implied by the equal sign, deficit spending is not the only way that private assets increase, or even the primary way. It's not the only source of private-sector “surplus” or “saving,” as is often suggested in MMT discourse. Not even close.

Start by thinking in terms of Household Net Worth. This measure has the virtue of encapsulating and telescoping all private-sector net worth, because households ultimately own firms, at zero or more removes, but firms don't own households (yet…). Citibank may own some GE shares, but Citibank is ultimately owned by households. Because: firms issue equity shares; households don't. It's an asymmetric, one-way ownership relationship.

Then take a look at this paragraph from MMTers extraordinaire Eric Tymoigne and Randall Wray:

MMT does differentiate between saving (in the flow of funds it is the change in net worth: ΔNW) and net saving (saving less investment). Net saving shows how the accumulation of net worth occurs beyond the accumulation of real assets. For the domestic private sector, this comes from a net accumulation of financial claims against the government and foreign sectors.