Principle of Insufficient Reason

A principle that was first enunciated by Jakob Bernoulli which states that if we are ignorant of the ways an event can occur (and therefore have no reason to believe that one way will occur preferentially compared to another), the event will occur equally likely in any way.

Keynes (1921, pp. 52-53) referred to the principle as the principle of indifference, formulating it as "if there is no known reason for predicating of our subject one rather than another of several alternatives, then relatively to such knowledge the assertions of each of these alternatives have an equal probability." Keynes strenuously opposed the principle and devoted an entire chapter of his book in an attempt to refute it.

The principle was also considered by Poincaré (1912).

REFERENCES:

Dupont, P. "Laplace and the Indifference Principle in the 'Essai philosophique des probabilités.' " Rend. Sem. Mat. Univ. Politec. Torino 36, 125-137, 1977/78.

Garibaldi, U. and Penco, M. A. "Probability Theory and Physics Between Bernoulli and Laplace: The Contribution of J. H. Lambert (1728-1777)." Proc. Fifth National Congress on the History of Physics, Rend. Accad. Naz. Sci. XL Mem. Sci. Fis. Natur. 9, 341-346, 1985.

Keynes, J. M. "Fundamental Ideas." Ch. 4 in A Treatise on Probability. Macmillan, 1921.

Hacking, I. "Jacques Bernoulli's Art of Conjecturing." British J. Philos. Sci. 22, 209-229, 1971.

Poincaré, H. Ch. 1 in Calcul des probabilités. Paris, 1912. Reprinted Jacque Gabay, 1987.