In sentences which refer to a hypothetical or counterfactual situation, some people, especially speakers of AmE, prefer to use the subjunctive form of the verb. The only verb in English which has a different form for the past subjunctive is BE - were is used for all persons:
I wish I were rich. (I am not rich)
If Philo were here, he would explain it better than I (Philo is not here).
Many speakers of BrE use the indicative form - they would use was in those two sentences. Although some people claim that was is incorrect, most descriptive grammarians consider its use acceptable.
If you are interested in a long discussion on this, try: If I "were" king instead of "was"
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