Error is a virus that tends to spread. As I have already hinted, the categories of circulating capital and of the wage fund tended and still tend to … - Paul Samuelson

Arrow’s general impossibility theorem does not disprove the existence of the Bergsonian social welfare function, neither does it disprove the existence of the Benthamite hedonistic function.

In the preface to the reissue of Risk, Uncertainty and Profit, Frank Knight makes the penetrating observation that under the conditions envisaged above the velocity of circulation would become infinite and so would the price level. This is perhaps an over-dramatic way of saying that nobody would hold money, and it would become a free good to go into the category of shell and other things which once served as money. We should expect too that it would not only pass out of circulation, but it would cease to be used as a conventional numeraire in terms of which prices are expressed. Interest bearing money would emerge. Of course, the above does not happen in real life, precisely because uncertainty, contingency needs, non-synchronization of revenues and outlay, transaction frictions, etc., etc., all are with us. But the abstract special case analyzed above should warn us against the facile assumption that the average levels of the structure of interest rates are determined solely or primarily by these differential factors. At times they are primary, and at other times, such as the twenties in this country, they may not be. As a generalization I should hazard the hypothesis that they are likely to be of great importance in an economy in which there is a “quasi-zero" rate of interest. I think by this hypothesis one can explain many of the anomalies of the United States money market in the thirties.

As old problems are conquered, we expect to turn up new problems. A discipline lives on its unsolvved problems; and so, for better or worse, economics is likely to be a lively subject for as many years ahead as man can see.