Counterfactual

A counterfactual conditional (abbreviated CF), in philosophy, is a subjunctive conditional containing an if-clause that is contrary to fact. The term counterfactual was coined by Nelson Goodman in 1947, extending Roderick Chisholm’s (1946) notion of a “contrary-to-fact conditional”.

• Causal information cannot be encoded as a set of beliefs (rejecting Ginsberg view of conterfactuals).
• It is difficult to fine-tune Lewis’s similarity measure to match causal intuition (rejecting Ramsey view of conterfactuals).

Pearl defines counterfactuals directly in terms of a structural equation model, a set of equations in which each variable is assigned a value that is an explicit function of other variables in the system.

Given such a model, the sentence “Y would be y had X been x” (formally, X = x > Y = y ) is defined as the assertion: If we replace the equation currently determining X with a constant X = x, and solve the set of equations for variable Y, the solution obtained will be Y = y. This definition has been shown to be compatible with the axioms of possible world semantics and forms the basis for causal inference in the natural and social sciences, since each structural equation in those domains corresponds to a familiar causal mechanism that can be meaningfully reasoned about by investigators.

See also

Books

• Judea Pearl (2000). Causality: Models, Reasoning, and Inference. Cambridge University Press.