Since the 1960s, Tobin has set himself the objective of developing a macroeconomic model more general than that specified by Keynes in the General Theory. In his work, he explicitely deals with financial intermediaries and elaborates a 'new view' which, in contrast with the 'old view', maintains that there are no reasons to attribute a special role to the banks. This paper critically analyses Tobin's theory and shows that this theory overlooks an important function of banks highlighted by Keynes, and that the specification of this banks' function is the necessary condition to highlight the most significant aspects of what Keynes calls a monetary economy. These points enable us to draw some observations about the question of the financial system regulation