Right now, deficits don’t matter — a point borne out by all the evidence. But there’s a school of thought — the modern monetary theory people — who say that deficits never matter, as long as you have your own currency.

I wish I could agree with that view — and it’s not a fight I especially want, since the clear and present policy danger is from the deficit peacocks of the right. But for the record, it’s just not right.

The key thing to remember is that current conditions — lots of excess capacity in the economy, and a liquidity trap in which short-term government debt carries a roughly zero interest rate — won’t always prevail. As long as those conditions DO prevail, it doesn’t matter how much the Fed increases the monetary base, and it therefore doesn’t matter how much of the deficit is monetized. But this too shall pass, and when it does, things will be very different.

So suppose that we eventually go back to a situation in which interest rates are positive, so that monetary base and T-bills are once again imperfect substitutes; also, we’re close enough to full employment that rapid economic expansion will once again lead to inflation. The last time we were in that situation, the monetary base was around $800 billion.

Suppose, now, that we were to find ourselves back in that situation with the government still running deficits of more than $1 trillion a year, say around $100 billion a month. And now suppose that for whatever reason, we’re suddenly faced with a strike of bond buyers — nobody is willing to buy U.S. debt except at exorbitant rates.

So then what? The Fed could directly finance the government by buying debt, or it could launder the process by having banks buy debt and then sell that debt via open-market operations; either way, the government would in effect be financing itself through creation of base money. So?

Well, the first month’s financing would increase the monetary base by around 12 percent. And in my hypothesized normal environment, you’d expect the overall price level to rise (with some lag, but that’s not crucial) roughly in proportion to the increase in monetary base. And rising prices would, to a first approximation, raise the deficit in proportion.

So we’re talking about a monetary base that rises 12 percent a month, or about 400 percent a year.

Does this mean 400 percent inflation? No, it means more — because people would find ways to avoid holding green pieces of paper, raising prices still further.

I could go on, but you get the point: once we’re no longer in a liquidity trap, running large deficits without access to bond markets is a recipe for very high inflation, perhaps even hyperinflation. And no amount of talk about actual financial flows, about who buys what from whom, can make that point disappear: if you’re going to finance deficits by creating monetary base, someone has to be persuaded to hold the additional base.