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The “is-ought fallacy” fallacy

Published online by Cambridge University Press:  14 October 2011

Mike Oaksford
Department of Psychological Sciences, Birkbeck College, University of London, London, WC1E 7HX, United Kingdom.
Nick Chater
Behavioural Sciences Group, Warwick Business School, University of Warwick, Coventry CV4 7AL, United Kingdom.


Mere facts about how the world is cannot determine how we ought to think or behave. Elqayam & Evans (E&E) argue that this “is-ought fallacy” undercuts the use of rational analysis in explaining how people reason, by ourselves and with others. But this presumed application of the “is-ought” fallacy is itself fallacious. Rational analysis seeks to explain how people do reason, for example in laboratory experiments, not how they ought to reason. Thus, no ought is derived from an is; and rational analysis is unchallenged by E&E's arguments.

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Copyright © Cambridge University Press 2011

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