Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

In a conditional sentence, choose verb tenses according to the type of condition expressed in the sentence
Verbs
Multilingual Writers and ESL Topics

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 49e 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.

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

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.

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

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 possibilities

If 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.

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 fact

For 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 27g on the subjunctive mood.)

Events that did not happen

In 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” on p. 228.)

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

EXERCISE 28-3

Edit the following sentences to correct problems with verbs. In some cases, more than one revision is possible. Possible revisions appear in the back of the book.

a. The electrician might have discovered the broken circuit if she inspected the wires thoroughly.

b. If Verena wins a scholarship, she would go to graduate school.

c. Whenever a rainbow appears after a storm, everybody came out to see it.

d. Sarah did not understood the terms of her internship.

e. If I live in Budapest with my cousin Szusza, she would teach me Hungarian cooking.