Counterfactual
A claim, hypothesis, or other belief that is contrary to the facts and suggests a hypothetical state of the world in which to assess the impact of an action.
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Origin
David Hume first articulated a counterfactual analysis of causation in 1748, proposing that cause and effect are linked by what would or would not have happened under different conditions. The idea received its rigorous philosophical treatment in 1973 from David Lewis, whose book Counterfactuals applied possible worlds semantics to conditional logic. Working independently, Robert Stalnaker had developed a parallel framework in 1968; together their work formed the Stalnaker–Lewis theory.
Updated February 22, 2026