The Mercantilistic-Keynesian Employment Theory Embraced All Essential Features of Modern Effective Demand Analysis

However, we do not want to examine further the factual conditions under which the Mercantilistic-Keynesian employment theory is valid. What we want to show is that this theory embraced in fact all essential features of modern "Effective Demand Analysis." As far as I can see, the man who developed this analysis most conclusively is John Law who, although generally not counted among the Mercantilists proper, is undoubtedly to be considered the strongest and most interesting exponent of their ideas.
--L. Albert Hahn, "Mercantilism and Keynesianism," in The Economics of Illusion: A Critical Analysis of Contemporary Economic Theory and Policy (New York: Squier Publishing, 1949), 108.

Keynes' "Monistic" Theory of Cash Demand for Hoarding Purposes: Interest Is the Reward for Not Hoarding

According to Keynes' liquidity preference theory, interest is paid for the "desire to hold wealth in the form of cash" and received as "the reward for parting with cash" against some instrument of saving. It is "the reward for not hoarding," not "the reward for not spending." In other words, the owner of a savings account receives interest because he does not hoard, not because he does not spend money; and he loses interest because he hoards money, not because he spends it. The demand for cash comes from the desire to transform savings accounts into cash. It is denied that money is demanded in order to be spent, not to be hoarded. In short, the switching from savings accounts into cash for hoarding, not the withdrawal of savings accounts for spending, is considered the only possibility. At least on the surface, this is a "monistic" theory of cash demand for hoarding purposes.

--L. Albert Hahn, "Anachronism of the Liquidity Preference Concept," in The Economics of Illusion: A Critical Analysis of Contemporary Economic Theory and Policy (New York: Squier Publishing, 1949), 147.

The School Most Enthusiastic for Monetary Manipulations Is the Mercantilist School and It Is Related to Keynesianism

It might therefore be appropriate to recall briefly the teachings of the school that has shown more enthusiasm for monetary manipulations than any other during history. We mean the teachings of the Mercantilists. 

The relationship of Keynesianism to Mercantilism of the sixteenth to the eighteenth centuries is well known. Keynes himself has pointed to it. He has said much in praise and in defense of mercantilistic theory and policy and against arguments presented by its classical critics.

--L. Albert Hahn, "Mercantilism and Keynesianism," in The Economics of Illusion: A Critical Analysis of Contemporary Economic Theory and Policy (New York: Squier Publishing, 1949), 106-107.