In 1964, when Sheldon Harnick wrote the lyrics for the musical Fiddler on the Roof, he had the poverty-stricken Russian milkman Tevye sing “If I were a rich man.”
In 1992, affluent rock star Bon Jovi sang “If I was your mother,” but then in 2008, Beyoncé sang “If I were a boy.”
Clearly, both forms persist in popular usage.
Curious to see how the two constructions compare in the world of pop music, I searched a site called ReverbNation. According to the search results, “If I Was” and” If I Were” as song titles are tied at “over 500 songs” each.
According to linguist Geoffrey Pullum, co-author of the Cambridge Grammar of the English Language (CGEL), there’s no significant difference between using was or were in what the CGEL calls “the irrealis form of the copula.” (A copula is what linguists call a word that links subject and predicate. Irrealis is unreal.) In Pullum’s view, both “if I was” and “if I were” mean the same thing in such a statement.
A web search will bring up both acceptance and rejection of the “if I was” construction. Merriam-Webster illustrates its discussion of the usage by pointing out that F. Scott Fitzgerald used both forms for statements of unreality. Here are two:
I wish I were twenty-two again … — F. Scott Fitzgerald, letter, 27 Dec. 1925.
… if I was Vassar, I wouldn’t take you … — F. Scott Fitzgerald, letter, 18 Apr. 1938
The M-W editor concludes:
Clearly there is a choice to be made here, and if Fitzgerald could use either form, so can others.
Unfortunately, not everyone will agree with Merriam-Webster on this one. To many people, “I wish I was a rich man” is not standard usage.
There are contexts in which “if I was” can be justified. For example, “If she was ill, no wonder she left the party early.”
In a statement that does not describe reality, or the possibility of reality, were is still the better choice–if only because a great many employers, clients, and customers still regard “if I was you” as nonstandard usage.