Modern Monetary Theory recognises that the government has infinite capacity to spend and that the constraint on spending is always inflation never insolvency. One of the many myths that crop up about MMT is that it allows an infinite size deficit. This is false. MMT has always stated that the limit to spending are the real resources available. This is just another way of saying spending can be inflationary. The inflation constraint has been dealt with elsewhere by all and sundry in the MMT community. Perhaps it is a question of solvency instead? The answer is simple how can a currency issuer go involuntarily broke? It can’t.
Many think it can because of the Government Budget Constraint (GBC). In the current orthodox economic view is that the budget must be financed either by printing money and/or borrowing money from the public.
Bill Mitchell explains the current orthodox view of the GBC this way:
Fiscal deficit = Government spending + Government interest payments – Tax receipts must equal (be “financed” by) a change in Bonds (B) and/or a change in high powered money (H)
However, this is merely an accounting statement. In a stock-flow consistent macroeconomics, this statement will always hold. That is, it has to be true if all the transactions between the government and non-government sector have been corrected added and subtracted.
So in terms of MMT, the previous equation is just an ex post accounting identity that has to be true by definition and has not real economic importance.
But for the mainstream economist, the equation represents an ex ante (before the fact) financial constraint that the government is bound by. The difference between these two conceptions is very significant and the second (mainstream) interpretation cannot be correct if governments issue fiat currency (unless they place voluntary constraints on themselves to act as if it is).
So you can see the difference is that the current orthodox view is that the GBC must be financed by printing money and/or borrowing money from the public and that the Modern Monetary Theory view is that a currency issuer can issue currency & bonds and the GBC is just an accounting identity. It is nothing to worry about.