Hello guys

I know we had a conclusion on the subject but I'd like to put some additional information. The article below is a description in a book (written in Japanese) by Late Dr Toshio Nakao, a scholar who taught the history of the English language in several colleges in Japan and in Great Britain.

Let's suppose someone ask to a group of people saying :"Who is the boss?" and let's see the historical change in the way English speakers answer to this question.
[1] Days of Old English
In the days when English people still retained case inflexions for nouns, A and B in the statement of "A is B" should be both in the forms of nominative case. As for the question "Who is the boss?", an grammatical answer should be "I am it". However, "It am I" was likely a more popular saying, because it was their linguistic custom in Old English to invert the subject (=I) and the complement (=it) when the complement is a pronoun."
[2] End of Middle English
The expression "It am I" continued to be spoken at least until the time of Chaucer. "Peter, it am I" quod she [Chaucer, , 1386]. However some people began to feel it was rather ungrammatical. It was because they thought that in English a noun that stands before a verb should be the subject of the sentence. So they took 'it' as the subject and 'I' as the complement, and revised the phrase into "It is I". It is I that am here in your syth [ 1450].
[3] Early Modern English
"It is me", what OED is still now calling as an 'uneducated speech', began as early as in 16 century. Shakespeare used the nominative me in (1591) : The dog is me, and I am my self. But its use has got popular since 18 century on. To dine with her and come at three! Impossible, it can't be me! [Swift 1733]. Why do modern day's English speakers feel "It is me" more natural than "It is I"? It is because they tend to think all a nominative pronoun should be in the status of the subject in a sentence and they tend to feel as if there are two subjects in the sentence "It is I".

What I have learned from this brief history of the expression "It is me" is that what expression is considered to be grammatical in a language is time dependent.

paco