Knightian decision theory. Part I

A theory of choice under uncertainty is proposed which removes the completeness assumption from the Anscombe–Aumann formulation of Savage's theory and introduces an inertia assumption. The inertia assumption is that there is such a thing as the status quo and an alternative is accepted only if it is preferred to the status quo. This theory is one way of giving rigorous expression to Frank Knight's distinction between risk and uncertainty. Received: 8 October 2001 / Accepted: 8 November 2001 The author is grateful to Martin Shubik for encouragement and long discussions. He is also grateful to Donald Brown, Edward Leamer, David Schmeidler, Martin Shubik, Sidney Winter, Asad Zaman and Arnold Zellner for calling his attention to relevant literature. Note of the Editor: Except for a few minor editorial changes, this article publishes content formerly circulated as Discussion Paper no.~807 of the Cowles Foundation at Yale University, November 1986.