Conditional tense

[gtkuk]

Why do we say "If I were you...." and not, "If I was you....? I believe it is the Mixed Conditional. But why don't we use "was"?

[Alan]

Actually, BrE speakers frequently do use 'was', but 'were' (a form known as the past subjunctive, used to refer to hypothetical present events and situations) is preferred by most AmE speakers.