conditional sentences

A sentence that states a condition and the result that depends on it.

A conditional sentence joins a subordinate clause that states a condition, usually introduced by if, to a main clause that states the result. The verb in the if clause shows how the speaker regards the condition, and the verb in the main clause follows from that choice. Three patterns cover most conditional sentences.

Open condition. The speaker leaves open whether the condition is true, and each clause takes the indicative in the tense that fits its own time: If the movers left at noon, the truck is on the highway now. The exception is a future condition, in which the if clause takes the present tense rather than will: If the inspector signs off on the forms, the crew will pour the foundation.

Hypothetical condition. For a condition contrary to present fact or unlikely in the future, the if clause takes a past form, and the main clause takes would, could, or might with the base form: If the clinic stayed open until nine, more patients could come after work. The past form marks the condition as remote from fact; it does not refer to past time.

Past counterfactual. For a condition contrary to past fact, the if clause takes the past perfect, and the main clause takes would have, could have, or might have with the past participle: If the pharmacist had checked the label, she would have caught the mistake. The past perfect places the condition in the past and marks it as unfulfilled.

The two clauses can refer to different times. A condition contrary to past fact can have a present result: If Laura had accepted the transfer, she would live in Denver now.

In a hypothetical condition, the verb be takes were with every subject, I, he, she, and it included: If the stadium were closer, we would walk to the game. When a condition concerns a past fact that may be true, the condition is open, and was is the standard form: If the guard was asleep, he missed the alarm. The choice changes the meaning: If the guard were asleep, he would miss the alarm treats the guard as awake.

Would marks the result, so it belongs in the main clause. Many people put would have in the if clause of a past counterfactual, but standard English uses the past perfect there: If I had known, not If I would have known. If I’d have known is nonstandard for the same reason; the standard contraction is If I’d known, in which ’d stands for had.

Would in the if clause is standard in two cases. It can express willingness, as in a request: If you would initial each page, we can file the lease today. It can also introduce an effect that follows the action of the main clause: If it would help, I could arrive early.

A condition can also be stated without if by placing had, were, or should before the subject. This inverted conditional is standard and more formal than the if form. Each auxiliary introduces one kind of condition.

Had I known means If I had known and introduces a past counterfactual.

Were she here means If she were here and introduces a hypothetical. With to and a base verb, were introduces a hypothetical future: Were the airline to cancel the route, the town would lose its only flight.

Should you need means If you should need and introduces an open condition that the speaker presents as less likely: Should you need a second key, ask the front desk.

In an inverted conditional, not follows the subject, and the auxiliary is never contracted: Had the pilot not noticed the warning light, the plane would have taken off. Hadn’t the pilot noticed the warning light? is a question, not a condition.

Examples

Use If the invoice came on Monday, accounting has logged it. (An open condition: the past indicative came states a past fact that may be true, and the main clause takes the present perfect its own time requires.)

Use If Jordan was at the rehearsal, he knows the new ending. (Was is standard: the condition is a past fact that may be true.)

Use If the elevator worked, we could move the piano upstairs this afternoon. (The past form worked marks a hypothetical: the elevator is out of service.)

Use Had the referee seen the foul, the goal would not have counted. (The inverted had introduces a past counterfactual: the referee did not see the foul.)

Avoid If the check would have cleared on Friday, we could have paid the plumber. (Would have in the if clause is the error: a condition contrary to past fact takes the past perfect, and would belongs to the result. Write If the check had cleared on Friday, we could have paid the plumber.)

Avoid If we’d have set out at six, we would have reached the cabin by nightfall. (’d have in the if clause is the error: whether ’d stands for would or had, a condition contrary to past fact takes had and the past participle alone. Write If we had set out at six, we would have reached the cabin by nightfall.)

Avoid If I was on this jury, I would vote to acquit. (Was is the error: the condition is contrary to present fact, so be takes were. Write If I were on this jury, I would vote to acquit.)