Wason selection task
The Wason selection task, commonly referred to as the four-card problem, is a logic puzzle in cognitive psychology designed to evaluate individuals' ability to apply deductive reasoning and falsification principles to test conditional rules. Developed by British psychologist Peter Cathcart Wason, the task presents participants with a conditional statement, such as "If there is a D on one side of the card, then there is a 3 on the other side," and four cards laid out face-up, each showing either a letter (D or k) or a number (3 or 7) from one side, with the opposite side unknown. The objective is to select only the cards that must be turned over to definitively determine whether the rule holds true or false for the entire set, with the logically correct choices being the D card (to check for a non-3) and the 7 card (to check for a D, as its presence would violate the contrapositive).[1] Despite its apparent simplicity, performance on the abstract version of the task reveals systematic biases in human reasoning, with meta-analytic evidence indicating that only approximately 19% of participants across numerous studies select the correct cards (p and not-q), while a majority erroneously include the not-p (k) or q (3) cards, often driven by a tendency toward confirmation rather than falsification.[2] This low success rate, first documented in Wason's original experiments where fewer than 10% succeeded, underscores the challenge of applying formal logic to abstract scenarios and has positioned the task as a cornerstone for studying confirmation bias.[1] Subsequent research has highlighted a content effect, where success rates dramatically improve—to around 64% in deontic (social contract or permission) versions, such as "If a person is drinking beer, then they must be over 19"—suggesting that contextual relevance, evolutionary adaptations for cheater detection, or pragmatic inferences facilitate reasoning when rules involve obligations or prohibitions.[2] The task's enduring influence spans theories of rational analysis, Bayesian modeling of data selection, and dual-process accounts of intuitive versus deliberative cognition, with over 200 experiments confirming its robustness in revealing discrepancies between normative logic and everyday inference.[2]Background
Origin and development
The Wason selection task was devised in 1966 by Peter Cathcart Wason, an English cognitive psychologist based at University College London.[3] Wason developed the task as an experimental tool to investigate human deductive reasoning processes, building on his prior research into cognitive biases.[4] It was first described in Wason's chapter titled "Reasoning," published in the edited volume New Horizons in Psychology by B. M. Foss.[5] In this work, Wason introduced the task to empirically demonstrate confirmation bias—the tendency to favor information that supports a hypothesis while neglecting evidence that could refute it—in the context of conditional statements.[6] The design drew inspiration from Karl Popper's philosophy of science, particularly the principle of falsification, which emphasizes testing hypotheses through potential disconfirmation rather than mere verification.[7] The task evolved from Wason's earlier experiments on inductive reasoning, such as the 2-4-6 problem introduced in 1960, which similarly highlighted confirmation-seeking behaviors but focused on rule discovery.[4] Initial studies using abstract versions of the selection task, involving letters and numbers, yielded low success rates, with approximately 10% of participants identifying the cards necessary to falsify the rule.[1] These findings underscored the challenges in applying logical falsification in non-concrete scenarios and laid the groundwork for subsequent research in the psychology of reasoning.Significance in cognitive science
The Wason selection task exemplifies confirmation bias, where individuals preferentially seek confirming evidence for a hypothesis while neglecting potentially falsifying information, a phenomenon first systematically demonstrated through Peter Wason's experimental paradigm. This bias highlights fundamental limitations in human hypothesis testing, as people often fail to select cards that could disprove a conditional rule, instead focusing on affirmative instances. Wason's work established this as a core cognitive error, influencing subsequent research on how such tendencies persist across diverse populations and contexts.[8] As a cornerstone in cognitive psychology, the task probes the distinction between deductive reasoning—requiring logical falsification—and inductive reasoning, which favors pattern confirmation, revealing systematic errors in abstract logical inference. It has become a benchmark for studying reasoning biases, with early experiments showing success rates as low as 10% in abstract forms, underscoring the challenge of applying formal logic in non-contextual scenarios. This has positioned the task as essential for exploring how cognitive processes deviate from normative models of rationality.[9] The task's influence extends to evolutionary psychology, notably through Leda Cosmides' application, which posited that enhanced performance on social contract versions reflects evolved cognitive modules for detecting cheating in cooperative exchanges rather than general logical ability. In the philosophy of science, it aligns with Karl Popper's falsification principle, illustrating why scientific progress demands rigorous disconfirmation over mere verification. By 2025, the task has been cited in over 2,000 studies, including meta-analyses that confirm persistent low performance rates of 10-25% on abstract rules across decades of replication.[10][11] Beyond psychology, the task informs applications in artificial intelligence, where models are evaluated for human-like reasoning errors to improve decision-support systems—recently including tests of large language models that exhibit similar confirmation biases on abstract versions—and in training programs that teach falsification strategies to mitigate biases in professional decision-making, such as in medicine and policy analysis.[12]Task Description
Standard presentation
In the standard presentation of the Wason selection task, participants are individually presented with four cards laid out on a table or screen, each showing only one side. These cards are drawn from a larger set where every card has a letter on one side and a number on the other. The experimenter provides a conditional rule, such as: "If there is a vowel on one side of a card, then there is an even number on the other side." The visible sides of the cards display an 'A' (vowel), a 'D' (consonant), a '4' (even number), and a '7' (odd number). Participants are instructed to select and turn over only those cards necessary to determine whether the rule holds true or false for the entire set, emphasizing the need to test for potential violations without unnecessary turns.[1] This abstract version relies on arbitrary letters and numbers to isolate pure logical reasoning. Concrete versions adapt the format to everyday scenarios for contextual relevance, such as the rule: "If a person is drinking beer, then they must be at least 19 years old," with cards showing "drinking beer," "drinking cola," "16 years old," and "25 years old." Participants receive the same instructions to select cards that could confirm or disconfirm the rule.[13] The task is typically conducted without time constraints in controlled settings, using paper-based materials in early studies or computerized interfaces in contemporary research, where selections are made by circling options, pointing, or clicking. Cards are arranged in random order to avoid positional biases, and the setup ensures participants understand that turning a card reveals the hidden side completely.[1]Logical structure of the conditional
The Wason selection task employs a conditional rule of the form "if P, then Q," where P represents the presence of a vowel on one side of a card and Q represents an even number on the other side. This rule is formally interpreted as a material conditional in propositional logic, denoted as P \to Q, which asserts that whenever the antecedent P is true, the consequent Q must also be true. The truth value of the material conditional P \to Q is determined by a standard truth table, which specifies its behavior across all possible combinations of truth values for P and Q:| P | Q | P \to Q |
|---|---|---|
| True | True | True |
| True | False | False |
| False | True | True |
| False | False | True |