if. Problems often arise in deciding whether if is introducing a subjunctive clause {'If I were …'} or an indicative one {'If I was …'}. The distinction is straightforward. When if introduces a notion that is hypothetical or improbable or clearly untrue, the verb should be in the subjunctive: 'If I were king …'; 'If he were in your shoes …'. But when the if is introducing a thought that is true or could well be true, the mood should be indicative: 'If I was happy then, I certainly am not now'. One small hint: if the sentence contains would or wouldn't, the mood is subjunctive, as in 'If I were you, I wouldn't take the job'.
( Bill Bryson )
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