The mental model theory of thinking and reasoning

The mental model theory has been extensively tested and experiments have corroborated several tell-tale signs of the use of mental models:

  • A mental model represents one possibility, capturing what is common to all the different ways in which the possibility may occur. Mental models represent explicitly what is true, but not what is false. These characteristics lead naive reasoners into systematic errors.
  • The greater the number of models that a task elicits, and the greater the complexity of individual models, the poorer performance is. Reasoners focus on a subset of the possible models of multiple-model problems – often just a single model – and are led to erroneous conclusions and irrational decisions.
  • Procedures for reasoning with mental models rely on counterexamples to refute invalid inferences; they establish validity by ensuring that a conclusion holds over all the models of the premises. These procedures can be implemented in a formal system; however current psychological theories based on formal rules (and most artificial intelligence programs) do not use them.

Mental models provide a unified account of deductive, probabilistic, and modal reasoning. People deduce that a conclusion is necessary – it must be true — if it holds in all of their models of the premises; they infer that it is probable — it is likely to be true — if it holds in most of their models of the premises, and they infer that it is possible — it may be true — if it holds in at least one of their models of the premises. Mental model researchers have investigated the role of models in many domains of reasoning including the following:

  • Reasoning with sentential connectives such as “or” and “and”.
  • Reasoning based on conditional assertions.
  • Reasoning with quantifiers such as “all”, “some”, and “none”, including syllogistic reasoning and reasoning with multiple quantifiers.
  • Counterfactual reasoning and reasoning about hypothetical or imaginary cases.
  • Informal everyday inferences and arguments.
  • Relational reasoning, including spatial reasoning and temporal reasoning.
  • Modal reasoning about what is possible and what is necessary.
  • Probabilistic reasoning.
  • Wason’s selection task.
  • Wason’s THOG task.
  • Reasoning by depressed or psychotic individuals.
  • Causal Reasoning
  • Deontic reasoning, including moral reasoning
  • Defeasible reasoning
  • Problem solving

Current challenges to model theorists are to explain reasoning about intentions, reasoning about other people’s inferences, and reasoning about concepts.

Phil Johnson-Laird and Ruth Byrne
May 2000 (updated July 2012)

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