M1-e: Verbs in conditional sentences

M1-eIn a conditional sentence, choose verb tenses according to the type of condition expressed in the sentence.

Conditional sentences contain two clauses: a subordinate clause (usually starting with if, when, or unless) and an independent clause. The subordinate clause (sometimes called the if or unless clause) states the condition or cause; the independent clause states the result or effect. In each example in this section, the subordinate clause (if clause) is marked SUB, and the independent clause is marked IND. (See B3-e on subordinate clauses.)

Factual

Factual conditional sentences express relationships based on facts. If the relationship is a scientific truth, use the present tense in both clauses.

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If the sentence describes a condition that is (or was) habitually true, use the same tense in both clauses.

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Predictive

Predictive conditional sentences are used to predict the future or to express future plans or possibilities. To form a predictive sentence, use a present-tense verb in the subordinate clause; in the independent clause, use the modal will, can, may, should, or might plus the base form of the verb.

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tip: In all types of conditional sentences (factual, predictive, and speculative), if or unless clauses do not use the modal verb will.

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Speculative

Speculative conditional sentences express unlikely, contrary-to-fact, or impossible conditions. English uses the past or past perfect tense in the if clause, even for conditions in the present or the future.

unlikely possibilitiesIf the condition is possible but unlikely in the present or the future, use the past tense in the subordinate clause; in the independent clause, use would, could, or might plus the base form of the verb.

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The writer does not expect to win the lottery. Because this is a possible but unlikely present or future situation, the past tense is used in the subordinate clause.

conditions contrary to factIn conditions that are currently unreal or contrary to fact, use the past-tense verb were (not was) in the if clause for all subjects. (See also G2-g, on the subjunctive mood.)

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The writer is not president, so were is correct in the if clause.

events that did not happenIn a conditional sentence that speculates about an event that did not happen or was impossible in the past, use the past perfect tense in the if clause; in the independent clause, use would have, could have, or might have with the past participle. (See also past perfect tense, M1-a.)

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The writer did not save more money and did not travel to Laos. This sentence shows a possibility that did not happen.