Counterfactual conditionals

A counterfactual conditional (abbreviated CF), is a conditional containing an if-clause which 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". The study of counterfactual speculation has increasingly engaged the interest of scholars in a wide range of domains such as philosophy, human geography, psychology, cognitive psychology, history, political science, economics, social psychology, law, organizational theory, marketing, and epidemiology.

In 1748, when defining causation, David Hume referred to a counterfactual case:

"… we may define a cause to be an object, followed by another, and where all objects, similar to the first, are followed by objects similar to the second. Or in other words, where, if the first object had not been, the second never had existed …" — David Hume, An Enquiry Concerning Human Understanding.

The difference between indicative and counterfactual conditionals, in a context of past time reference, is one of emphasis. This can be illustrated with a pair of examples in which the if clause is in the past indicative in the first example but in the pluperfect subjunctive in the second:

The protasis (the if clause) of the first sentence may or may not be true according to the speaker, so the apodosis (the then clause) also may or may not be true; the apodosis is asserted by the speaker to be true if the protasis is true. In this sentence the if clause and the then clause are both in the past tense of the indicative mood.

In the second sentence, the speaker is speaking with a certainty that Oswald did shoot Kennedy. According to the speaker, the if clause is false, so the then clause deals with the counterfactual result, i.e., what would have happened. In this sentence the if clause is in the pluperfect subjunctive form of the subjunctive mood, and the then clause is in the conditional perfect form of the conditional mood.

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