“It is I” vs. “It is me”

How about:
It is I who knocked on the door
but
It is me you are looking for.
?

Have to agree... there's correct and correct. Grammatically correct "It is I" sounds stilted most of the time. I knock on Mom's door, she shouts to see who it is (cause it might not be worth climbing out of the easy chair for just anybody), I shout back "It's me." Call my brother on the phone, leave message "It's just me, call me back" which strongly presumes that after 45+ years he is able to identify this ME from the voice. Etc., etc. I am pretty darn much a stickler for proper grammar, but I am lax on this one.

Your grammar teacher is right. Yeah I know, it sounds funny to knock on you're friend's door and when they ask "who is it?" you answer "it's I." But "to be" is not a transitive verb. In fact, the funny properties of "to be" are highlighted by the fact that many languages (Hebrew, Russian, Arabic...) don't even have such a verb in the present tense. In those languages, you would literally say "it I" (it would not make sense to say in Russian "eto menya," see www.painintherussian.com). Not only is "to be" a funny verb, but English makes very funny use of its case system. Back in the day (c. 600 AD) when English's case system was more important in English grammar than it is today, transitive verbs sometimes took the genetive (i.e., "drincan wines," to drink of wine), and the application of the accusative, dative, and instrumental cases was virtually arbitrary. Given that kind of historical background for English cases, it isn't surprising that a given verb will take a case that does not necessarilly make sense (in this instance, nominative for "to be").

What does correct mean? Long ago when I was young, the rule was that the verb to be takes no object - there is a grammatical logic to it. However, people commonly say "it is me" and that form is now 'correct' by usage.

When living in Denmark and learning Danish at school, my teacher corrected me for saying "det er jeg" - in Danish, "it is I" is consider *wrong*, and I should have said "det er mig"!

Right and wrong are just notions...