Conditionals are sentences like the following:

(1) If Oswald did not kill Kennedy, then someone else did

(2) We will not go on the trip if it rains tomorrow

(3) If Oswald had not killed Kennedy, then someone else would have

(4) We would be playing tennis if it were not raining

Conditionals are often believed to be analyzable into a two-place sentence connective and two constituent sentences, the antecedent (the sentence introduced by "if") and the consequent. (Thus, [3] may be analyzed into a binary connective ["If it had been the case that …, then it would have been the case that …"] and the constituent sentences "Oswald did not kill Kennedy" and "someone else did [kill Kennedy].")

Many philosophers believe that there is an important difference between conditionals like (1) and (2) (which are commonly called "indicative conditionals"), and those like (3) and (4) (called "subjunctive" or "counterfactual"). Following Ernest W. Adams (1970), one can motivate this idea...