SIMILARITY, PLAUSIBILITY, AND JUDGMENTS OF PROBABILITY

Judging the strength of an argument may underlie many reasoning and de cision-making. tasks. In this article, we focus on ''category-based'' arguments, in which the premises and conclusion are of the form All me mbers of C have property P, where C is a natural category. An example is ''Dobermanns have sesamoid bones. Therefore, German shepherds have sesamoid bones.'' The strength of such an argument is reflected in the judged probability that the conclusion is true given that the premise s are true. The processes that mediate such probability judgments depe nd on whether the predicate is ''blank'' - an unfamiliar property that does not enter the reasoning process (e.g., ''have sesamoid bones'') - or ''non-blank'' - a relatively familiar property that is easier to reason from (e.g., ''can bite through wire''). With blank predicates, probability judgments are based on similarity relations between the pr emise and conclusion categories. With non-blank predicates, probabilit y judgements are based on both similarity relations and the plausibili ty of premises and conclusion.