Hypothetical conditional clauses
In the second type of conditional clause, the hypothetical conditional, the past tense is used to indicate modal remoteness; the event or state coded in the condition is seen as less likely to be fulfilled, though not hypothetically impossible. The structure is If + past tense remote (i.e. without any relation to past time) + would or another ‘remote’ modal such as could or might preceding the lexical verb in the main clause.
14 If you left now, you would /might catch the last train.
15 If Tom passed his driving test, he would soon be buying a car.
If the verb in the conditional clause is be, the subjunctive mood form were is preferred, in good usage, to the indicative was, not only with plural subjects but also singular. The expression If I were you is conventionally used to give advice:
16 If I were you, I wouldn’t agree to carry a package for someone on a flight.
Were and the modal should are also used to add an element of tentativeness. In 17, if is replaced by subject- operator inversion using the subjunctive were + to-infinitive. In 18 the verb is should with subject-operator inversion, and in 19 should occurs together with if. All three forms imply a greater degree of remoteness, whether of unlikelihood, politeness or deference.
17 Were anyone to ask me to carry a package on a flight, I would certainly refuse.
18 Should you decide to come to the concert, we can meet at the concert hall.
19 If you should change your mind, just let me know.
