Yes, verbs are moody little buggers, and one of their weirder moods is called the subjunctive. This form of the verb, which expresses an improbable condition, one contrary to fact, or a wish, command, or desire, is a booby trap for many writers. Its use in both spoken and written English is nearly extinct, but it survives in certain traditional phrases such as:
If I were you. . . . Wish you were here. . . . If I were a rich man. . . . Come what may. . . . Far be it from me. . . .
The condition contrary to fact is the construction that is the biggest bugaboo in the use of the subjunctive. Example:
If such a procedure as this were not used, many patients would not survive.
This example is correctly expressed. But many clauses introduced by if do not express a condition contrary to fact but merely a condition or contingency. In such cases, the subjunctive mood is incorrect. Clauses introduced by as if or as though, however, usually—repeat, usually—express an unreal condition (a condition contrary to fact). Therefore, you must use the subjunctive mood of the verb with them in most cases. Example:
She looked at me as if I were Vlad the Impaler.
Now look at this sentence:
If she were not on the scene, his chances would improve.
Is the subjunctive mood of the verb (were) correct in this case? Is the sentence expressing a condition contrary to fact or simply a contingency? It’s talking about a contingency—an event that may or may not happen. She may or may not be on the scene. So using the subjunctive mood is incorrect. The verb, therefore, should be was.
Now you can amaze your friends by explaining when to use was and when to use were.