MMT and policy assignment in an open economy context: Simplicity is useful, oversimplification not so much

Modern Monetary Theory (MMT) has recently received significant attention in academic and policy circles. Critics question the sustainability of MMT‐prescribed approaches to fiscal and monetary policy, especially over extended periods of time, in the presence of international financial markets, and for developing country governments that borrow in foreign currency. I formalize some of these arguments using a dynamic, open economy, Tobin‐Markowitz portfolio balance environment that takes into account: (1) the role of expectations in the foreign exchange market and the feedback mechanisms between these and the exchange rate and inflation, and (2) interactions between the current account, debt accumulation, and the goods market. I show that continuous monetary accommodation of fiscal policy by a consolidated authority that operates along MMT‐prescribed lines is likely to generate instability and make it hard to maintain full employment with stable inflation. Importantly, this is true even in the absence of rational forward‐looking expectations or sovereign foreign indebtedness.