Counterfactual

From EvaluationWiki

A hypothesis about what might be the case, but isn't in fact the case. Such hypotheses are often invoked in the attempt to define causation, but without significant success. Thus, X is said to cause Y when if X had not happened (the counterfactual), Y would not have happened. But Y is often over-determined by the cluster of circumstances making up the environment, that is, it would have occurred even if X had not occurred, although in fact X did cause Y.