Suppression of valid inferences and knowledge structures: The curious effect of producing alternative antecedents on reasoning with causal conditionals
H. Markovits et F. Potvin, Suppression of valid inferences and knowledge structures: The curious effect of producing alternative antecedents on reasoning with causal conditionals, MEM COGNIT, 29(5), 2001, pp. 736-744
These studies looked at the difficulty that reasoners have in accepting con
ditional ("If P then Q") major premises that are not necessarily true empir
ically, as a basis for deductive reasoning. Preliminary results have shown
that when reasoners are asked to produce possible alternate antecedents to
the major premise ("If A then Q"), they paradoxically tend to deny the modu
s ponens (MP) inference ("If P is true, then Q is true"). Three studies fur
ther explored these results. The first study gave university students paper
-and-pencil tests in which instructions to "suppose that the major premise
is true" was followed by a request to determine the next number in a sequen
ce, to retrieve information unrelated to the premises, or to retrieve a pos
sible case of "If A then Q." Relative to a control group, reasoners asked t
o produce an alternative antecedent showed a significant tendency to deny t
he MP inference, whereas no such tendency was observed for the two other ta
sks used. A second study compared performance on a condition in which reaso
ners were asked to produce an alternative antecedent with that when they we
re given an explicit alternative. Premises used in this study were such tha
t the latter alternative antecedent was also spontaneously produced by over
7096 of reasoners. Results showed that the tendency to refuse the MP premi
se could not be accounted for by the specific nature of the alternative pro
duced. A third study found that the tendency to refuse the MP inference aft
er producing an alternative antecedent was affected by the number of "disab
ling conditions" (i.e., conditions that allow "P to be true" and "Q to be f
alse") available for the major premise. These results are interpreted as be
ing consistent with a model that supposes that logical reasoning requires s
elective inhibition of real-world knowledge.