subjunctive mood

The form used for a condition contrary to fact or for a demand.

For a present condition contrary to fact, use were: If the bridge were open, the drive would take ten minutes. With wish, as if, and as though, an untrue statement also takes were: The intern gives orders as though he were the manager. In these constructions, only be has a distinct subjunctive form. Other verbs use the ordinary past: Sarah wishes the library were open on Sundays, but Sarah wishes the library opened earlier.

For a past condition that may be true, use the indicative: If the clerk was at the desk at noon, she saw the courier.

For a demand, recommendation, or necessity after that, use the base form of the verb: The lease requires that each tenant carry insurance. The negative places not before the base form, and the passive uses be: The coach asked that players not leave the bench; The judge ordered that the files be sealed.

Examples

Use If she were here, she would sign. (Were marks a present condition contrary to fact.)

Avoid If she was here, she would sign. (Was is the error: a present condition contrary to fact takes were. Write If she were here, she would sign.)

Use The rule requires that he file the brief. (After requires that, the verb takes the base form.)

Avoid The rule requires that he files the brief. (Files is the error: a that clause after a verb of demand takes the base form. Write The rule requires that he file the brief.)