Conditional reasoning concerns "if-then" (conditional) statements: "If it rains, the streets will be wet." Two inferences are logically valid: modus ponens (given "if P then Q" and P, conclude Q) and modus tollens (given "if P then Q" and not-Q, conclude not-P). Two are invalid: affirming the consequent (given "if P then Q" and Q, concluding P) and denying the antecedent (given "if P then Q" and not-P, concluding not-Q). Human performance reveals systematic departures from logical norms.
The Wason Selection Task
Peter Wason's (1966) four-card selection task is the most studied paradigm in reasoning research. Given the rule "If a card has a vowel on one side, it has an even number on the other side" and four cards showing A, K, 4, 7, only about 10% of participants correctly select A and 7 (the only cards that could falsify the rule). Most select A and 4 (confirmation bias). However, when the same logical structure is framed as a social contract ("If you drink beer, you must be over 21"), performance dramatically improves, suggesting that evolutionary-adapted cheater detection mechanisms facilitate reasoning about social rules.
Cheng and Holyoak proposed that people reason about conditionals using pragmatic reasoning schemas — abstract knowledge structures induced from everyday experience with classes of situations such as permissions, obligations, and causation. These schemas provide domain-specific reasoning rules that facilitate correct inferences within their scope. This account explains why deontic (permission/obligation) versions of the selection task are easy while arbitrary conditional rules are hard.