 It is easy to imagine a world where  (3)  is true, and  (4)  false. Consider a world like ours where Kennedy was assassinated. Further suppose Oswald didn’t do it, but some lone fanatic did for deeply idiosyncratic reasons. Then  (3)  is true and  (4)  false. Another aspect of the contrast between indicative and subjunctive conditionals is illustrated in  (5)  and  (6).  