Is the conjunction fallacy tied to probabilistic confirmation?
Crupi et al. (2008) offer a confirmation-theoretic, Bayesian account of the conjunction fallacy—an error in reasoning that occurs when subjects judge that Pr(h1 & h2|e) > Pr(h1|e). They introduce three formal conditions that are satisfied by classical conjunction fallacy cases, and they show that these same conditions imply that h1 & h2 is confirmed by e to a greater extent than is h1 alone. Consequently, they suggest that people are tracking this confirmation relation when they commit conjunction fallacies. I offer three experiments testing the merits of Crupi et al.’s account specifically and confirmation-theoretic accounts of the conjunction fallacy more generally. The results of Experiment 1 show that, although Crupi et al.’s conditions do seem to be causally linked to the conjunction fallacy, they are not necessary for it; there exist cases that do not meet their three conditions in which subjects still tend to commit the fallacy. The results of Experiments 2 and 3 show that Crupi et al.’s conditions, and those offered by other confirmation-theoretic accounts of the fallacy, are not sufficient for the fallacy either; there exist cases that meet all three of CFT’s conditions in which subjects do not tend to commit the fallacy. Additionally, these latter experiments show that such confirmation-theoretic conditions are at best only weakly causally relevant to the presence of the conjunction fallacy. Given these findings, CFT’s account specifically, and any general confirmation-theoretic account more broadly, falls short of offering a satisfying explanation of the presence of the conjunction fallacy.
KeywordsConjunction fallacy Confirmation Bayesianism Probability Experimental philosophy
Unable to display preview. Download preview PDF.
- Carnap R. (1950) Logical foundations of probability. University of Chicago Press, ChicagoGoogle Scholar
- Eells E. (1982) Rational decision and causality. Cambridge University Press, Cambridge, UKGoogle Scholar
- Good I. J. (1950) Probability and the weighing of evidence. Griffin, LondonGoogle Scholar
- Keynes J. M. (1921) A treatise on probability. Macmillan, LondonGoogle Scholar