ケインズの蓋然性論とナイトの不確実性論

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1 I Yasuhiro Sakai / J M probability uncertainty J M Keynes, The General Theory of Employment, Interest and Money 1921 A Treatise on Probability winter / No.398

2 silver spoon Frank H. Knight, wooden spoon 1921 Risk, Uncertainty and Profit the miracle year of The Ethics of Competition Milton Friedman Homer Jones George StiglerAllen Wallis

3 7 26 II 1 probability favorable cases to the whole number of cases possible probability 3 50 probability probability theory A Treatise on Probability 2 PROBABILITY source: Oxford Dictionary of English noun the quality or state of being probable; the extent to which something is likely to happen or be the case. [mathematics] the extent to which a event is likely to occur, measured by the ratio of the probability 1989 probabilities Borel winter / No.398

4 O A O A 1 1 O impossibility I certainty A O I numerically measurable probability U, V, W, X, Y, Z nonnumerical probabilities VA W, X Y X Y W V A V Z W, X, Y U V, W, X, Z 053

5 2 O A I O 0 A 60 I O OAI I 100 A 60 3OVWXI U V V W X Y W Z W W45 65 X W X 1 4 VA VAW A 1 partial order O A O A X A OZWYI W Z Y W W A Z A 3 interval valued probability Keynes 1921, p.161 Brady winter / No.398

6 X A Z65 W Y45 Z W W Y 6 OUI practical man 055

7 the degree of belief Gillies winter / No.398

8 700 AKB

9 Skidelsky winter / No.398

11 animal spirits winter / No.398

12 III uncertainty probability 061

13 probability situation a priori probability statistical probability estimates, judgment managerentrepreneur winter / No.398

14 IV J M

15 winter / No.398

16 A IS LM

17 Akerlof, G.A. and Shiller, R.J. (2009)/ Animal Spirits: How Human Psychology Drives the Economy, and Why it Matters for Global Capitalism / Princeton Univ. Press. Brady, M / J.M. Keynes Theory of Decision Making, Induction and Analogy: The Role of Interval Valued Probability in His Approach / Xlibris Corporation. Borel, E / Valeur pratique et philosophie des probabilities./ 1942 Borel, E / Les probabilities et la Vie, QUE SAIS-JE, Presses Universitaires de France. / 1967 Dillard, D / The Economics of John Maynard Keynes: The Theory of a Monetary Economy / Crosby Lockwood. Gillies, D / Philosophical Theories of Probability / Routledge probability Hicks, J / Causality in Economics / Basil Blackwell Keynes, J. M / A Treatise on Probability / Macmillan..Keynes, J. M / The General Theory of Employment, Interest and Money / Macmillan Klein, L / The Keynesian Revolution / Macmillan. Knight, F / Risk, Uncertainty and Profit / Univ., of Chicago Press. Knight, F / The Ethics of Competition / Univ. of Chicago Press Leijonhufvud, J / On the Keynesian Economics and the Economics of Keynes: A Study in Monetary Theory / Oxford Univ, Press c winter / No.398

18 1955 Skidelsky, R / Keynes: The Return of the Master / Peters Fraser & Dunlop Group

19 J. M. Keynes' Theory of Probability versus F. H. Knight's Theory of Uncertainty: Reflections on the Miracle Year of 1921 Yasuhiro Sakai The main purpose of this paper is to critically discuss and lucidly compare J. M. Keynes ( ) and F. H. Knight ( ), two towering figures in the history of economic thought. It is in 1921 that they both published apparently similar books on risk, probability and uncertainty. While Knight contribution on the economics of risk and uncertainty has been well-known and very influential in the economics profession, Keynes accomplishments on probability and uncertainty have been more or less underestimated in the dark shadow of his most famous book (1936) The General Theory of Unemployment, Interest and Money. The present paper aims to focus on an earlier yet equally important book (1921) A Treatise on Probability, hopefully shedding a new light on his outstanding ideas and everlasting influences on his later works including The General Theory. According to Keynes, many probabilities, which are incapable of numerical measurement, can be placed nevertheless between numerical upper and lower limits. Keynes has demonstrated whether and to what extent animal spirits contributes to the working and performance of the market economy. Remarkably, Keynes' concept of probability and uncertainty can be well-compared to Knight's distinction between a measurable risk and a non-measurable uncertainty. I believe that it is high time for us to unify Keynes and Knight into a new, comprehensive approach to very complex human behavior. 068 THE HIKONE RONSO 2013 winter / No.398

20 J. M. Keynes' Theory of Probability versus F. H. Knight's Theory of Uncertainty Yasuhiro Sakai 069

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