The role of logical and nonlogical factors in making inferences about category membership

Three postulates are proposed concerning the manner in which persons infer the validity of propositions that do not necessarily follow logically from the information available. These postulates assume that subjects first attempt to identify the propositions that are most and least likely to follow from the information given. They then use their beliefs in these propositions as anchors, relative to which the validity of other propositions is evaluated on the basis of both logical and nonlogical criteria. Two experiments are reported in which these postulates are used successfully to diagnose the logical and nonlogical factors that underlie inferences based upon both single statements and sets of syllogistically related propositions. The implications of the proposed postulates for existing formulations of social inference and cognitive organization are discussed.