The rule that I was taught is that was is for things that could be true but aren't, and were is for things that could never be true.

So, if I was an airline pilot is OK because conceivably I could retrain as a pilot, if I wanted.

But if I were you is right because I will never be you.

The rule you were taught is wrong, Daniel.

The few subjunctive forms that are left can all be stated in other fashions using language that isn't subjunctive in form. We use lexical verbs to state subjunctive/contrary to fact situations all the time.

If I lived in Bangkok, ... // If I had a million dollars, ... // If I hadn't been born, ... .

Just as we can use the past time FORM of lexical verbs to describe contrary to fact situations, so too we can use 'was'. It's not as formal as the subjunctive form 'were' but it means the same thing.

There's not a speaker of English anywhere who thinks that "If I was you" means that the speaker is saying "I am you".

"If I were you" means the same thing as "If I was you". They both entail that I am not you.

Of course, we can and do use 'was' to state "allowing that that's true,

If she was at the party, she sure was quiet.

The rule that I was taught is that was is for things that could be true but aren't, and were is for things that could never be true.

So, if I was an airline pilot is OK because conceivably I could retrain as a pilot, if I wanted.

But if I were you is right because I will never be you.

The rule you were taught is wrong, Daniel.

The few subjunctive forms that are left can all be stated in other fashions using language that isn't subjunctive in form. We use lexical verbs to state subjunctive/contrary to fact situations all the time.

If I lived in Bangkok, ... // If I had a million dollars, ... // If I hadn't been born, ... .

Just as we can use the past time FORM of lexical verbs to describe contrary to fact situations, so too we can use 'was'. It's not as formal as the subjunctive form 'were' but it means the same thing.

There's not a speaker of English anywhere who thinks that "If I was you" means that the speaker is saying "I am you".

"If I were you" means the same thing as "If I was you". They both entail that I am not you.

Of course, we can and do use 'was' to state "allowing that that's true":

If she was at the party, she sure was quiet.