Usage Note: Many conditional (if ... then) constructions seem bewilderingly picky about which tenses, moods, and auxiliaries may go into them, particularly those that have to do with a counterfactual or make-believe world—one that the writer thinks is likely to be false but whose implications are worth exploring. But the grammatical requirements for such counterfactual sentences are quite straightforward: 1. The if-clause must have a verb in the conditional subjunctive mood (which many linguists call by the Latin name irrealis to distinguish it from the ordinary English subjunctive). When referring to situations in the present, this mood is identical to the preterite or past-tense form (If you danced better ... ) except for the verb be, whose irrealis is were rather than was (If he were rich ... ). When a writer wants to refer to a situation that hypothetically could have occurred in the past, a more remote past form must be used—the past perfect or the pluperfect (If you had danced better ... ; If he had been rich ... ). 2. The then-clause must contain would or a similar modal auxiliary such as could, should, or might. A large percentage of the Usage Panel disapproves of past counterfactual constructions using did rather than had: in 2011, 74 percent disliked If I didn't have my seatbelt on, I'd be dead, and 89 percent found it unacceptable to say If he didn't come to America, our team never would have won the championship. Forms using would have are somewhat more acceptable: the sentence If she would have only listened to me, this never would have happened was acceptable to 33 percent of the Panel in 2016. · When the situation described by an if clause is not presupposed to be false, that clause must contain an indicative verb: If Kevin was out sick yesterday, he will probably work late today. Note also that the presence of the modal verb would in the main clause should not be taken as a sign that the verb in the if clause must be in the subjunctive, if the content of that clause is not presupposed to be false: He would always call the office if he was (not were) going to be late for work. · According to the traditional rule, the subjunctive is not used following verbs such as ask or wonder in if clauses that express indirect questions, even if the content of the question is presumed to be contrary to fact: We wondered if dinner was (not were) included in the room price. · With all deference to the traditional rules, it should be noted that a survey of the prose of reputable writers over the past 200 years would reveal a persistent tendency to use the indicative was where the traditional rule would require the subjunctive were. A sentence beginning If I was the only boy in the world, while not strictly correct, is wholly unremarkable. · In informal writing both if and whether are standard in their use to introduce a clause indicating uncertainty after a verb such as ask, doubt, know, learn, or see: We shall soon learn whether (or if) it is true. In such contexts, however, the use of if can sometimes create ambiguities. Depending on the intended meaning, the sentence Let her know if she is invited might be better paraphrased as Let her know whether she is invited or If she is invited, let her know. · When used as a coordinator, the phrase if not always signals a contrast, but it can have almost contradictory meanings, depending on the context. Sometimes it can mean "but not," as in She won her team's admiration, if not its award, for her performance in the playoffs and The board was encouraged, if not convinced, by the budgetary projections. At other times, especially when there is a comparison of two adjectives or noun phrases in which the second represents a significant increase in degree above the first, if not usually means "and even," as in This job will be difficult, if not impossible and The law practice includes clients from all over the state, if not the country. Since many sentences of this kind can be interpreted one way or the other, it is important that the context make clear what sort of contrast is being indicated by if not. See Usage Notes at doubt, should, wish.