If + were or if + was

That's a question many ESL students ask. The answer is: usually either were or was can be used, the former being more likely in formal English

"If she was/were offered the job she'd take it."

"If Tom was/were here he'd know what to do."

But were is a little more usual than was in the advice form If I were/ was you I would/should . . . :

"If I were you I would wait a bit," he said.

Were is also more usual in the infinitive construction:

If Peter were/was to apply for the post he 'd get it.

However: Were, not was, is used when the auxiliary is placed first:
"Were I Tom I would refuse."
When if means "since" was cannot be replaced by were, were can replace was after if only and wish.

Note: if + subject + auxiliary can be replaced in formal English by inversion of auxiliary and subject with if omitted:

If he had known . . . = Had he known . . .
If I were in his shoes . . . = Were I in his shoes . . .
If you should need anything . . . = Should you need anything. . .

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