Reader Ali Abuzar wants us to: elaborate the difference and usage of
1.It is me.
2.It is I.
3.This is me.
4.This is I.
5.This is Mr. XYZ.
Items 1. and 2: It is me. It is I.
Back in the 18th century, when scholars were fiercely debating English grammar in an effort to “ascertain” and “fix” it, one of the proposed rules relating to pronouns was that a pronoun in the nominative case (what we now call a “subject pronoun”) must follow a form of to be:
It is I.
It is we.
It is they.
This rule is based on a rule that exists in Latin.
The existence of this rule in any language, however, does not prevent most English speakers from saying It’s me.
When someone phones me and says: “Is Maeve Maddox there?”
my response is always “This is she.” That’s the way my momma brought me up to answer the phone. She also taught me to say “To whom do you wish to speak?”
However, in face to face conversation, I’m much more likely to say It’s me.
It’s me is idiomatic English. It is I is not.
That’s not to say that the usage of to be followed by a nominative pronoun is either dead or deserves to be. It’s just not used by all speakers on all occasions.
There’s a familiar hymn whose chorus contains the line
“Here I am, Lord. Is it I, Lord?”
Writers of fiction often use the differing forms as character tags.
Items 3. and 4: This is me. This is I.
The only context for “This is me” that I can think of (except maybe in answering the telephone) would be in describing photos to another person:
This is me the summer after I graduated.
This is me when I joined the Marines.
This is I would sound strange in this context.
Item 5: This is Mr. XYZ.
This is the normal construction for such a statement. Ex. This is the author of my favorite novel. This is Mr. Biceps, my gym teacher.