Reasoning Competence

In the 1970s, various experiments were carried out on
ordinary people"s reasoning powers suggesting our natural
ability to reason does not match up to the normative
standards endorsed in logic and probability theory. The
two most famous of these have come to be termed the
selection experiment, and the conjunction experiment (or
Linda experiment). In the first, Peter Wason asked
subjects to test a rule for cards with numbers on one side
and letters on the other, such as "If the card has a vowel
on one side, it has an odd number on the other" (Wason
1971). Wason"s basic finding was that very few subjects
selected the two cards that are necessary to test such a
rule, suggesting that they do not understand the logic of
conditionals (that they are false just if the antecedent is
true and the consequent false). In the second experiment,
Kahneman and Tversky told subjects a story about a
woman called Linda, and then gave them a list of
statements about Linda concerning what kind of occupation
she has and/or what she does in her free time, and
asked them to rank the statements from most to least
likely. Nearly all subjects ranked the statement Linda is a
bank teller and active in the feminist movement as more
likely than Linda is a bank teller, which contravenes a
fundamental theorem of statistics to the effect that the
probability of any single event A can never be lower than
the probability of both A and some other event B. (Cf.
Tversky & Kahneman 1983.)