지난 12월 28일 아산 세미나에서 제가 심학10도 중 제2도는 단지 물리학에 국한된 것이 아니라 근대경제학 또는 신고전파 경제학에도 해당되지 않을까 말씀드렸습니다.

구체적인 '변화의 원리'는 가령 뉴턴 방정식과는 다르지만, 처음 상태와 나중 상태를 연결하고 '변화의 원리'에 따라 예측적 앎을 추구한다는 점에서 사실상 고전역학의 틀 안에 있다는 주장이었습니다.

장회익 선생님의 대답은 그런 유비가 성립할 수는 있겠지만 그렇다고 해서 경제학을 고전역학과 같은 것으로 보는 것은 과도한 면이 있다는 것이었습니다.

제가 주목한 대목은 종종 언급되긴 하지만 널리 알려지지는 않은 아담 스미스와 아이작 뉴턴의 관계, 그리고 근대경제학에서 가장 중요하다고 흔히 이야기되는 '한계혁명'을 주도한 레옹 발라스(Marie-Esprit-Léon Walras, 1834-1910)의 저작과 주장이었습니다.

아담 스미스는 <국부론(An Inquiry into the Nature and Causes of the Wealth of Nations)>으로 널리 알려져 있는 정치경제학의 시조입니다. 스미스가 경제학을 '사회 물리학 social physics'라 불렀다는 것은 덜 알려져 있지만, 스미스가 뉴턴과 그의 자연철학을 매우 높이 평가했고 또 잘 이해하고 있었으며, 자신이 경제학 사상에 이를 녹여내려고 애썼다는 점을 경제사학자들이 주목하고 있습니다.

레옹 발라스는 경제의 탐구에 뉴턴 역학을 모범으로 삼아 적용하려 애썼고, 상품시장의 균형에 대한 분석에서 엄밀한 미분방정식을 사용했습니다.

물론 단순히 미분방정식을 썼다는 것과 뉴턴 역학을 모범으로 삼았다는 것만으로 고전역학과 신고전 경제학이 같은 개념틀 안에 있었다고 주장하는 것은 분명히 좀 과도합니다.

그래도 고전역학이라는 물리학의 한 흐름과 신고전파 경제학을 비교하는 일은 더 깊이 고민해 볼만한 주제라 생각됩니다.

아래 인용문과 참고자료 몇 개를 덧붙입니다.

"뉴턴의 원대한 계획은 자연철학의 일반법칙을 확정함으로써 위대한 수학적 원리를 발견하는 것이었으며, 여러 다양한 영역의 지식들을 지배하는 원리들을 발견하려는 방대한 운동의 촉발시켰으며, 그 지식들에는 경제현상에 대한 탐구도 당연히 포함되었다. 아담 스미스의 경우 뉴턴적 우주에 대한 집착은 천문학의 역사를 다루는 그의 저서에만 표현된 것이 아니다. 그 저서는 <자연철학의 수학적 원리>의 저자의 가르침을 직접 사용하고 있었다. 아담 스미스는 <국부론> 전체에 걸쳐 셀 수 없이 많은 곳에서 여기저기 흩어져 있는 대상들의 묶어주는 보이지 않는 연쇄와 관계에 대한 뉴턴의 포괄적 개념을 적용했다. 이는 관찰과 실험을 통해 유도된 일반원리가 지배하는 질서 속으로 그 대상들을 통합시키는 것이었다. 다르게 말하면, 눈에 보이는 질서는 실재의 삶의 관찰된 사실들을 조직하는 보이지 않는 구조로 설명된다는 것이다. 가장 자주 인용되는 예 중 하나는 어떤 재화의 시장가격이 어떻게 자연가격 근처에서 넘나드는지 설명하기 위해 암묵적으로 중력법칙을 끌어들인 경우이다. 정치경제학을 사람의 고의적 개입을 방지하는 추상적 과학으로 발전시키지는 못했지만, 아담스미스가 뉴턴이 도입하고 발전시킨 철학적 및 과학적 체계로부터 생겨나는 규준을 지켜나가려 애썼다는 점은 의심의 여지가 없다."

"Let us take as an illustrative example, the clearly visible relationships of similarity between the works of Newton and Smith, which have not escaped the attention of specialists (Hetherington 1993). Newton’s grand design, which consisted of discovering great mathematical principles for determining the general laws of natural philosophy, set in motion a vast movement seeking to discover the principles that governed the various fields of knowledge, naturally including the study of economic phenomena. As far as Smith was concerned, his adherence to the Newtonian universe was expressed not only in his works on the history of astronomy in which he made direct use of the teachings of the author of the Principia. At countless points throughout the Wealth of Nations, Smith incorporated Newton’s overall conception of the invisible chains and relationships that gave coherence to scattered objects by integrating them into an order governed by general principles that were induced through observation and experimentation. Or, in other words, the visible order is explained by an invisible structure that organises the observed facts of real life. One of the most frequently quoted examples is that of the implicit recourse to the law of gravitation to explain how the market price gravitates around the natural price of a certain good. Although he did not succeed in turning political economy into an abstract science immune to the deliberate intervention of man, which would call for an alteration of the conditions for the existence of certain laws, there is no doubt that Smith sought to maintain some obedience to the criteria arising from the philosophical and scientific system introduced and developed by Newton.

[On this subject, see Cohen (1993), and, in particular, Redman, who summarises the importance of Newton’s legacy for the formation of a social science, as follows: ‘After Newton had founded order and harmony in the physical universe by discovering the laws that govern its movements, philosophers reasoned that disorder must be man-made and could be averted by studying human nature and ascertaining the natural laws or connecting principles that govern society. The existence of guiding social principles was taken for granted; the search for them than became a primary goal. The scholars of this age were convinced that immutable laws such as those reigning in the physical universe existed in society and in mental states of human beings’ (Redman 1997, p. 111).]"

José Luís Cardoso (2004). "Natural Law, Natural History and the Foundations of Political Economy" in John B. Davis, Alain Marciano and Jochen Runde (eds.) The Elgar Companion To Economics and Philosophy. Edward Elgar. (https://bit.ly/39osRH1)

"Walras, a radical by temperament, who conceived himself to have few intellectual antecedents save his father, inspired chiefly by the formal constructions of Classical mechanics, sets out the elements of his economic universe and their interconnectedness with the unadorned rigour of elementary differential equations -equilibrium in the product market, equilibrium in the market for factor services, equilibrium in the capital market and equilibrium in the value of money. The exposition is prolix and repetitive. But its width and logical inevitability is highly impressive; and, on the surface at any rate, there is little compromise or continuity with the constructions of the past."

L. Robbins (1970). The Evolution of Modern Economic Theory. Palgrave Macmillan. p. 24.

Arnaud Diemer et Hervé Guillemin (2011). "L'économie politique au miroir de la physique : Adam Smith et Isaac Newton" Revue d'histoire des sciences 2011/1 (Tome 64), 5-26. [https://bit.ly/2Q5k2u7] English translation "Political Economy in the Mirror of Physics: Adam Smith and Isaac Newton" [https://bit.ly/2sxrVQ2]

"... economists conventionally take it for granted that Smith applied Newton’s method to political economy. Because Newton’s method is thought to be similar to that of modern mainstream economics, the association of Smith with Newton is taken to bolster further the claim that modern mainstream economics continues the Smithian tradition. Support for this commonly accepted view is gathered from Smith’s panegyric attitude to Newton’s conception of philosophy. ... As an offspring of the same tradition, Walras, the architect of the ‘equilibrium system’, has been set alongside Newton, the discoverer of the ‘world system’ (Samuelson, 1952, p. 61). In this framework, Newton’s atomistic/mechanistic description of the celestial order provides evidence that Smith initiated the tradition of neoclassical and modern mainstream economics, having the same underlying ontological preconceptions that are pervasive and fundamental in the development of general economic equilibrium theory since Walras, whose achievement represents ‘the peak of neoclassical economic’ (ibid.)." [Leonidas Montes (2003) "Smith and Newton: some methodological issues concerning general economic equilibrium theory" Cambridge Journal of Economics, Vol. 27, No. 5 pp. 723-747, 인용문은 pp. 723-4.]

"But in fact Smith invoked the ‘Newtonian method’ in some of his more obscure works, and most economists and historians seem to have accepted this view. Mark Blaug (1980, p. 57), for instance, argues that Smith’s two major works, The Theory of Moral Sentiments and The Wealth of Nations, ‘must be regarded as deliberate attempts by Smith to apply this Newtonian method first to ethics and then to economics.’ Henry Bitterman (1940, pt. I, p. 502; in Wood, 1984, p. 197) indicates that Smith’s ‘procedure was an application of the techniques of Newtonian experimentalism to the question of morals.’ Andrew Skinner (1974, p. 182) writes that ‘Smith made much of the Newtonian “method” of argument’ and that there is no doubt that Smith’s economics ‘was originally conceived in the image of Newtonian physics’ (Skinner, 1979, p. 110; in Wood, 1984, p. 739). Norris Hetherington (1983, p. 497) sets forth the thesis that ‘Adam Smith’s efforts to discover the general laws of economics were directly inspired and shaped by the example of Newton’s success in discovering the natural laws of motion.’"
[Redman, D. A. 1993. Adam Smith and Isaac Newton, Scottish Journal of Political Economy, vol. 40, no. 2, pp. 210-230.
https://doi.org/10.1111/j.1467-9485.1993.tb00651.x]