Steve Randy Waldman has a good post on Interfluidity in which he attempts to form a synthesis between New Keynesians (NKs), post-Keynesians (PKs) and Market Monetarists (MMs).
Waldman actually exposes a bit of a fault with post-Keynesianism: what exactly are the policy prescriptions? Or, more specifically: how should monetary policy be conducted? PKs generally want to channel bank’s lending to the right people; we’re generally in favour of fiscal stimulus during downturns; Steve Keen has a policy prescription for redefining shares that I’m not entirely sure I understand the implications of, but it would be hard to say anything about a shared stance on monetary policy.
Waldman fills this gap by assuming that PKs don’t have a problem with NGDP targeting in principle, though they may doubt its practicality at the zero bound. However, I have spoken before about how NGDP targeting ignores the role of interest rates in determining not only the rate but the type of investment that takes place – instead assuming that macroeconomic policy can only reliably influence nominal variables. Scott Sumner, in fact, appears to believe that under NGDP targeting, the interest rate would be irrelevant.
Sumner is actually incredibly vague about why NGDP is the correct indicator for monetary policy: he has previously refused to discuss transmission mechanisms, and appears to think the the general public understand what the monetary base is, a position that goes hand in hand with his emphasis on expectations. In fact, I’d go so far as to say the entire thing is becoming circular: the CB controls NGDP so it should target NGDP – we will judge this by the level of NGDP.
PKs & MMTers, contrary to MMs & NKs, view interest rate policy as exogenous, and the only monetary variable that the CB can reliably control. In fact, as Edward Harrison notes, this is probably the major difference between exogenous versus endogenous money.
The endogenous view lends itself to the views of Keynes himself, who saw low rates as the appropriate monetary stance. In this view, interest rates are a cost of investment and so if they increase it will have two effects:
(1) Net investment will decrease;
(2) Businesses that do invest will be forced to seek higher returns and therefore take more risk. This can lead to speculative bubbles.
However, evidence suggests that businesses making investment decisions do not look at short term interest rates – both because they are prone to changes, and because they are too, well, short term. The Radcliffe Report, for example, emphasises that business decisions are far more heavily influenced by long term rates of interest, and also by expectations over the future path of the long term rate of interest. Thus, successful monetary policy lies in a credible commitment to, and execution of, permanently low long term rates. This also entails that monetary authorities have discretion over their jurisdiction, so capital controls would be a requirement.
As PKs & MMTers generally reject the IS/LM approach to the interest rate, generally sympathise with the views of Keynes himself and generally disregard ‘libertarian’ considerations when discussing international stabilisation, I do not see much of a reason that they should object to such a policy prescription.