Usage and Grammar
Q. Dear CMOS Editors, Although strict grammar would suggest that “if I had been you, I wouldn’t have done that” is correct, I feel that using “if I had been you” in this case instead of “if I were you” implies that the condition of my being you is impossible only in the past and may somehow have become more possible as time went on. Because it is not a changeable condition—I cannot be you, whether in the past or the present—I feel that “if I were you” is the right conditional to use in this example. I have not been able to find an authoritative explanation either way. What do you reckon?
A. This isn’t philosophy—it’s just grammar. “If I were you” puts the reader in the present. If you want to stage “if I were you” in the past, it becomes “if I had been you.”