A PROBABILISTIC-INTERPRETATION OF IF-THEN

This study proposes that subjects interpret thematic conditionals (''i f p then q'') probabilistically in solving conditional reasoning probl ems. Experiment 1 found that subjects' correct responses increased wit h the perceived probability of 4, given p for each of the four forms o f conditional arguments: modus ponens (MP), modus tollens (MT), denial of the antecedent (DA), and affirmation of the consequent (AC). Exper iment 2 ruled out two alternative explanations based on the comprehens ibility of conditionals and on subjects interpreting conditionals as b iconditionals. In Experiment 3, subjects solved two types of problems: (a) complete probabilistic problems, such as ''If p then q; knowing p ; how probable is q'', and (b) reduced probabilistic problems, such as ''Knowing p; how probable is q?'' Two sources of information that det ermine the observable reasoning responses are identified. One source o f information is based on one's general knowledge, and another is base d on taking all premises into account.