If I Was vs. If I Were

Don’t Say: If I was you, I wouldn’t wear horizontal stripes.
Say Instead: If I were you, I wouldn’t wear horizontal stripes.

Here’s Why: We need “were” instead of “was” here be¬cause we’re in the subjunctive mood. We know it’s the sub¬junctive because the signs are there: the use of “if,” and the condition contrary to fact—in this case, the fact that I cannot be you. Let’s look at a few more examples of the correct use of “was” and “were”:

I wish Jane were planning to go with us.
(The expression of a wish is the key indicator that we’re in the subjunctive mood here, and that makes this use of “were” correct.)

If Tom were in charge instead of Maria, we’d be fine!
(The meaning here is that Tom is not in charge, so the condition referred to is in opposition with reality. There¬fore, we’re in the subjunctive and “were” is correct.)

If Jack was at home, Sue must have been with him.
(Despite the “if’ that begins this sentence, we’re not in the subjunctive in this case. The meaning of the sentence is not a condition contrary to fact, or a wish or a suggestion. The implication is that Jack probably was at home. So “was” is correct.)