R. Hertwig et G. Gigerenzer, The 'conjunction fallacy' revisited: How intelligent inferences look like reasoning errors, J BEHAV DEC, 12(4), 1999, pp. 275-305
Findings in recent research on the 'conjunction fallacy' have been taken as
evidence that our minds are not designed to work by the rules of probabili
ty. This conclusion springs from the idea that norms should be content-blin
d - in the present case, the assumption that sound reasoning requires follo
wing the conjunction rule of probability theory. But content-blind norms ov
erlook some of the intelligent ways in which humans deal with uncertainty,
for instance, when drawing semantic and pragmatic inferences. In a series o
f studies, we first show that people infer nonmathematical meanings of the
polysemous term 'probability' in the classic Linda conjunction problem. We
then demonstrate that one can design contexts in which people infer mathema
tical meanings of the term and are therefore more likely to conform to the
conjunction rule. Finally, we report evidence that the term 'frequency' nar
rows the spectrum of possible interpretations of 'probability' down to its
mathematical meanings, and that this fact rather than the presence or absen
ce of 'extensional cues' - accounts for the low proportion of violations of
the conjunction rule when people are asked for frequency judgments. We con
clude that a failure to recognize the human capacity for semantic and pragm
atic inference can lead rational responses to be misclassified as fallacies
. Copyright (C) 1999 John Wiley & Sons, Ltd.