A HYPOTHESIS-ASSESSMENT MODEL OF CATEGORICAL ARGUMENT STRENGTH

According to the proposed hypothesis-assessment model, the strength of inductive categorical arguments, such as {All Robins Have Substance X therefore All Birds Have Substance X}, is determined by the same fact ors that affect hypothesis plausibility in the everyday social milieu. The premises of such arguments are viewed as evidence and the conclus ion is viewed as a hypothesis. Specifically, the proposed model predic ts that the perceived strength of general-conclusion categorical argum ents will be a function of (a) the number of premises that instantiate the conclusion; (b) the scope of the conclusion; and (c) the number o f accessed alternatives to the conclusion. In Experiment 1, one group rated the strength of individual arguments and another constructed sup erordinate hypotheses in response to the premise information alone. Mo st of the variance in perceived argument strength was accounted for by the proposed predictors, R = .94. Experiment 2 employed a new set of arguments and included an additional forced-choice condition in which subjects had to choose the stronger of two arguments. Again, the corre lation between predictors and argument strength was high, R = .91, and , all significant forced-choice preferences except one were correctly predicted by the model. The one unpredicted preference suggests' the n eed to include conclusion accessibility as a fourth factor. Also, on a subset of the forced-choice pairs in which no significant preference was observed, two distinct patterns of responding were detected - one predicted and the other unanticipated. Some strengths and limitations of the proposed hypothesis-assessment model are discussed in light of these results.