Nonmonotonicity and human probabilistic reasoning
Abstract
Nonmonotonic logics allow—contrary to classical (monotone) logics—
for withdrawing conclusions in the light of new evidence. Nonmonotonic
reasoning is often claimed to mimic human common sense reasoning. Only
a few studies, though, have investigated this claim empirically. system p
is a central, broadly accepted nonmonotonic reasoning system that proposes
basic rationality postulates. We previously investigated empirically
a probabilistic interpretation of three selected rules of system p. We
found a relatively good agreement of human reasoning and principles of
nonmonotonic reasoning according to the coherence interpretation of system
p.
This study reports an experiment on the cautious monotonicity
Rule and its “incautious” counterpart that is not contained in system
p, namely the monotonicity Rule. In accordance with our previous results,
the data suggest that people reason nonmonotonically: the subjects
in the cautious monotonicity condition infer significantly tighter intervals
close to the coherence interpretation of system p compared with
the subjects in the incautious monotonicity condition where rather wide
(and hence non-informative) intervals are inferred.