
Opening page to American philosopher Alan Nelson's 1992 chapter "Human Molecules" outlining the view that the "economic agent" model should correctly be the "human molecule" model. [1]

Opening page to American philosopher Alan Nelson's 1992 chapter "Human Molecules" outlining the view that the "economic agent" model should correctly be the "human molecule" model. [1]

In famous publications, Human Molecules is a twenty-one-page 1989 manuscript turned 1992 book chapter focused on the postulate that “economic agents” can be modeled “human molecules”, namely defining each person as an individual molecule, by American philosopher Alan Nelson. [1]

The chapter originated from a 1989 manuscript “Human Molecules”, by Nelson, that resulted to form a chapter in the 1992 book Post-Popperian Methodology of Economics, along with a followup rebuttal chapter, American economics professor Bruce Caldwell, and response chapter, by Nelson; and has been cited by the 2009 Oxford Handbook of Philosophy of Economics, among others, as the originator of the economic agent as human molecule model of people, in economics. [2]

Overview
The opening 1947 quote by Dutch-born American theoretical physicist and economist Tjalling Koopmans, noted for his efforts to apply mechanics, physics, and thermodynamics to the study of economics, is representative of the theme of Nelson's chapter and overall approach:

“While it was long possible and sometimes tempting for physicists to deny the usefulness of the molecular hypothesis, we economists have the good luck of being some of the ‘molecules’ of economic life ourselves, and of having the possibility through human contacts to study the behavior of other ‘molecules’.”

In other words, Koopmans, a Nobel Prize winner in economics and noted quantum chemical physicist, suggests that the time has come for scientists to stop denying the "human molecular hypothesis", i.e. humans are molecules, and to begin working this hypothesis for its usefulness and fruit. Nelson recalls, loosely, that he got the title of his chapter from Koopmans.

Nelson, in his chapter, expands on this premise by positing that dated idea of "economic agents" should be replaced by the postulate that people are molecules and that we should turn to physics, thermodynamics, and statistical mechanics to explain the behavior of people, in an economic sense, on the premise that these sciences have successfully been employed to explain the behavior of molecules, such as in explaining the behavior of a confined system of gas molecules. Nelson uses equations such as the Boyle-Charles's law, the standard equation for kinetic energy, and how economic agents might conform to a one-dimensional Maxwell distribution equation, among others. The following is representative quote from the chapter:

“A second kind of independent evidence concerning behavior of individual molecules is that the hypothesis that temperature is proportional to E permits the derivation of a wide variety of important theoretical results that are experimentally confirmed, as any textbook or statistical mechanics reveals. It is questionable whether economic assumptions about individuals produce the same variety of theoretical results and whether these results have been, or can be, experimentally tested. It is this third kind of indirect evidence that is most interesting in the present case.”

Nelson calls his theory the "Standard Model of Reduction" (SMR), which he says loosely follows the 1961 work of Czech-born American philosopher of science Ernest Nagel. [3]

Commentary
Nelson's chapter on human molecules was followed up by fifteen-page chapter "Commentary", by American economics professor Bruce Caldwell, wherein Caldwell outlines the overall historical view that most attempts towards physical science reduction methods fail and that in Nelson's case he has misunderstood the economic enterprise in his effort to find solution in physics. [4]

Reply
The third chapter in this series, is a four-page rebuttal chapter by Nelson. [5]

References
1. Nelson, Alan. (1992). “Human Molecules”, in: Post-Popperian Methodology of Economics, ch. 3, pgs. 113-33) by Neil De Marchi. Kluwer Academic Press.
2. (a) Nelson, Alan. (1989). “Human Molecules”, Unpublished Manuscript, Department of Philosophy, University of California, Irving.
(b) Nelson, Alan. (1990). “Human Molecules”, Unpublished Typescript. Department of Philosophy, University of California, Irving.
(c) Kincaid, Harold and Ross, Don. (2009). Oxford Handbook of Philosophy of Economics (pg. 394). Oxford University Press.
(d) Janssen, Maarten C.W. (1993). Microfoundations: a Critical Inquiry (behavior of in ‘individual’ humans and molecules, pg. 14; “Human Molecules” (1992), Nelson, pg. 125. Routledge.
(e) Mayer, T. and Heathfield. (1993). Truth Versus Precision in Economics (“Human Molecules” (1992), Nelson, pg. #). Langue: Anglais.
(f) Hoover, Kevin. (2006). “Microfoundations and the Ontology of Macroeconomics” (pg. 16: “Human Molecules”, Nelson, 1992), Presented at the conference on Issues in Philosophy of Economics, University of Alabama, Birmingham, 19-21 May.
(g) Ellis, Brian D. (2001). Scientific Essentialism (“Human Molecules” (1992), Nelson, pg. 170-87, 300). Cambridge University Press.
3. Nagel, Ernest. (1961). The Structure of Science. Harcourt, Brace, and World.
4. Caldwell, Bruce J. (1992). “Commentary on Alan Nelson’s ‘Human Molecules’”, in N. De Marchi (ed.) Post-Popperian Methodology of Economics. Recovering Practice. Boston: Kluwer Academic Publishers, pgs. 135-49.
5. Caldwell, Bruce J. (1992). “Reply to Bruce Caldwell's Commentary on ‘Human Molecules’”, in N. De Marchi (ed.) Post-Popperian Methodology of Economics. Recovering Practice. Boston: Kluwer Academic Publishers, pgs. 135-49.