Frank Hahn believed in throwing students in at the deep end — or so it seemed to me when, within weeks of my arrival at Cambridge as a 21 year old Research Student, he insisted I present my initial ideas on the foundations of monetary theory at his weekly seminar. I was petrified but somehow managed to give a half-decent lecture before a standing-room only audience in what used to be called the “Keynes Room” in the Cambridge Economics Department.
(It helped that a few months earlier, as a final year undergraduate at the LSE, I had been required to give a lecture at ACL Day’s Seminar on international monetary economics. It is a practice I came to follow with my students in due course, as there may be no substitute in learning how to think while standing up.)
I shall try to publish exactly what I said at my Hahn-seminar when I find the document; broadly, it had to do with the crucial problem Hahn had identified a dozen years earlier in Patinkin’s work by asking what was required for the price of money to be positive in a general equilibrium, i.e. why do people everywhere hold and use money when it is intrinsically worthless. Patinkin’s utility function had real money balances appearing along with other goods; Hahn’s “On Some Problems of Proving the Existence of an Equilibrium in a Monetary Economy” in Theory of Interest Rates (1965), was the decisive criticism of this, where he showed that Patinkin’s formulation could not ensure a non-zero price for money in equilibrium. Hence Patinkin’s was a model in which money might not be held and therefore failed a vital requirement of a monetary economy.
The announcement of my seminar was scribbled by a young Cambridge lecturer named Oliver Hart, later a distingushed member of MIT and Harvard University.
Independent Indian: Work & Life of Professor Subroto Roy 
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