Jaakko Hintikka

I agree with Jaakko Hintikka that the so-called “conjunction fallacy” of Kahneman and Tversky is no fallacy. I prefer a different explanation of the mistake made these authors (Levi 1985). Experimental subjects are invited to rank a set of propositions about Linda with respect to how probable, credible or likely they are on the basis of information given about a 31-year Linda. The task is to rank the set of hypotheses. Hintikka suggests that the experimental subjects think of the propositions as testimony of witnesses and have a prior view (relative to the background information contained in the sketch of Linda’s character) of the reliability of witnesses who testify to T and who testify to T&F. A witness who testified to T would be judged less reliable than a witness who testified to T&F. Hence, so Hintikka claims, the probability of T conditional on the biographical information about Linda and the testimony of the unreliable witness who testifies to T is less than the probability of T&F conditional on the biographical information about Linda and the testimony of the reliable witness who testifies to T&F. So T&F is ranked over T. If I have understood Hintikka’s suggestion correctly, he has not succeeded in saving the rationality of the experimental subject. In the first place, nothing in the scenario suggests that the hypotheses in question are or ever have been the testimony of any witnesses. But suppose we waive that point and accept Hintikka’s elaboration according to which the experimental subject takes one witness to have testified that T and another that T&F. So the total relevant evidence is now the background biography for Linda (E) and the testimony of both witnesses. If, as Hintikka, along with Kahneman and Tversky, seem to think, the experimental subjects are ranking the propositions on the list with respect to probability and these probabilities are posteriors conditional on the the total relevant information available, the comparison being required is a comparison using the same probability evaluation. To assign probability to T higher than the probability for T&F where these two posterior judgments are constituents of the agent’s probability judgment in a single context is simply incoherent. If it is claimed that the contexts are different, then the pair of probabil-