Full Idea
A counterfactual conditional (or 'counterfactual') is a proposition or sentence of the form 'If it had been the case that p, then it would have been the case that q', or 'If it were the case that p, then it would be the case that q'.
Gist of Idea
Counterfactuals say 'If it had been, or were, p, then it would be q'
Source
Thomas Mautner (Penguin Dictionary of Philosophy [1996], p.114)
Book Reference
Mautner,Thomas: 'Dictionary of Philosophy' [Penguin 1997], p.114
A Reaction
The first statement refers to the past, but the second (a subjunctive) refers to any situation at any time. We know more about inferences that we could have made in the past than we do about what is inferable at absolutely any time.