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History of Political Economy 33.3 (2001) 411-435
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David Hume on Experimental Natural Philosophy, Money, and Fluids
'Tis evident, that all the sciences have a relation, greater or less, to human nature; and that however wide any of them may seem to run from it, they still return back by one passage or another. Even Mathematics, Natural Philosophy, and Natural Religion, are in some measure dependent on the science of Man.
—David Hume, A Treatise of Human Nature
Among Enlightenment philosophers, David Hume (1711–1776) provided one of the most extensive arguments for the study of human nature. Even mathematics and natural philosophy depend upon our human faculties, as is made plain in the above assertion taken from the introduction to his Treatise of Human Nature (1739–40). As part of his efforts to develop the moral sciences, Hume cast aspersions on those engaged in the natural sciences, ranging from their inability to know the inner constituents of matter and force, to a propensity for becoming overly enamored with the efficacy of a single, purportedly universal principle such as gravitational attraction (Hume [1739–40] 1978, 64, 159;  1985e, 159–61). Much of book 1 of the Treatise leaves one wondering [End Page 411] if knowledge of the natural world is possible at all.1 Like Giambattista Vico and Baron de Montesquieu before him, Hume's critical stance toward the natural sciences was used to pave the way for the cultivation of the moral sciences, as laid out in books 2 and 3 of the Treatise, his essays on political economy, and his monumental History of England.
Although Hume's primary focus was directed toward human nature, I will argue here that the broader framework of his inquiry was the natural realm and that his knowledge of natural philosophy seeped into his moral philosophy and political economy more specifically.2 My argument is reinforced by noting that for Hume a typical event includes causal links with both the natural and the moral realms, and that there are few isolated moral phenomena. An understanding of economic phenomena such as money and prices would thus necessitate some attention to the physical setting offered by nature. As Hume ( 1985b, 324;  1985b, 329) observed, the world had been so designed such that its diverse “soils, climates, and geniuses” insured “mutual intercourse and commerce.” A richer understanding of physical nature would thus facilitate a deeper understanding of the moral realm, just as natural philosophy stemmed from a fuller understanding of human nature.
Drawing on the work of Michael Barfoot and others, I will show that Hume was well acquainted with natural philosophy, and that there are aspects of his monetary thought which reflect that knowledge. Barfoot (1990, 165) has conjectured that Hume's study of hydrostatics played a role in his emphasis on the flow and circulation of money, particularly in the essay “Of the Balance of Trade.” In that essay, Hume drew explicit analogies between money and water, making much of the tendency of water to reach its own level. But in Hume's essay “Of Money,” I believe a different set of properties was at work. Although Hume initially depicts money as the “oil” that lubricates the wheels of trade, there is no explicit mention of water. Rather, money is treated as a fluid in more general terms. Hume may well have developed his insights by drawing on recent experiments on the so-called electric fluid. I have not been [End Page 412] able to locate statements whereby Hume explicitly links electricity and money, and in that sense my argument is the weaker. My argument draws upon circumstantial evidence and thus reaches only a tentative conclusion. Nonetheless, I believe that it would be difficult to explain some of the more striking aspects of Hume's monetary theory without drawing these connections.
Eugene Rotwein, perhaps contrary to his better intentions, established the tradition (in 1955) of treating nine of Hume's essays, including “Of Money” and “Of Interest,” as distinctively economic. Eight of these essays were first published...