Which is correct to say: “It's me” or “It's I”?
Tonight I watched a movie (The Gospel of John) in which Jesus said (as quoted from the written Gospel of John), "It is I."
How does this expression differ from "It is me?"
Both expressions mean the same thing.
However, both of these pronouns have different rules of usages. In this case, they are both correct, because in some cases, like this case, they are interchangeable, but there are also instances when one of them can be used, but not the other:
"I" is a first person singular subject pronoun.
"Me" is a first person singular object pronoun.
Usually, there are interchangeable, as in the above example, but the bottom line is, don't use a subject pronoun and an object pronoun together. For example,
In the case of nouns, like "John and I" vs. "John and me", just substitute the appropriate pronoun for "John", and determine whether it is correct or not. For example:
So, you would know that "John and me" is an incorrect usage in this case.
Edit: As @MT_Head very kindly pointed out, there are cases when the noun can be replaced by a subject pronoun, and in other cases, by an object pronoun. In each case, substitute the correct pronoun and determine whether or not it is correct.
Note that many answers on this page (such as Bill and Ham_and_Bacon) describe English pronoun case after conjunction (and), which is not necessarily the same as after copula (be).
To quote from the clear explanation:
To summarize the situation, It is me is the more commonly spoken form, while It is I is commonly written, taught in school, and sometimes spoken.
There is no difference - I think it is just grammar. You just use them in different places. For example;
So I you should use
In a stage of life where I was more patient with the world, I would have tried to say this more politely. But basically, there is a class of people poorly educated in language/lingusitics but who wish to pretend otherwise that insist, for various spurious, easily falsifiable reasons, that instead of saying "It is me" (which is a natural, grammatical utterance in English), one 'should' say "It is I". The same people probably believe that homeopathic remedies will cure their brain cancer.
Maybe read "Language Myths" ed Bauer/Trudgill to see why it's a load of nonsense...
The way it was explained to me when I was a teenager, that finally caused the penny to drop was:
The 'me' or I has to stand alone. If you take the other elements out of the sentence does one or other of the pronouns sound right.
eg.1. "Sally and me went to the movies." does not sound right if you take Sally out of the story. (Me went to the movies.) So, this sentence should be: Sally and I went to the movies.
eg.2. "Benny met Sally and I in the mall." Once again, if you take Sally out the the story, it doesn't sound right. (Benny met I in the mall.) You would more naturally say, "Benny met me in the mall. So the correct way to say this sentence would be: Benny met me and Sally in the mall.
Thirty years later I still have to sometimes mentally make the me or I stand alone before I commit myself to a sentence.
"It is me" is ungrammatical. Transitive verbs, like speak take a subject and an object. Thus,
The verb to be is not transitive, but copular. It takes a subject and predicate. Thus,
Also, it must be
Edit: Please see @krubo's excellent answer below.
Edit: RegDwight is right that “It is I” is very formal for speech, and few people talk like this anymore.