About the age-long conflict between it is I and it is me, no more need be said than that, in the present stage of the battle, most people would think "it is I" pedantic in talk and "it is me" improper in writing.
What calls more for examination is the practice of using I for me in combination with some noun or other pronoun, e.g. "between you and I", "let you and I go". Why this has become so prevalent is not easy to say. Perhaps it comes partly from an excess of zeal in correcting the opposite error. When Mrs. Elton said "Neither Mr. Suckling nor me had ever any patience with them", and Lydia Bennet "Mrs. Forster and me are such friends", they were guilty of a vulgarism that was, no doubt, common in Jane Austen's day, and is not unknown today. One might suppose that this mistake was corrected by teachers of English in our schools with such ferocity that their pupils are left with the conviction that such combinations as you and me are in all circumstances ungrammatical. But that will not quite do. It might explain a popular broadcaster's saying "that's four to Margaret and I", but it cannot explain why Shakespeare wrote: "All debts are cleared between you and I".
It is the combination of oneself with someone else that proves fatal. The official who wrote: "I trust that it will be convenient to you for my colleague and I to call upon you next Tuesday" would never, if he had been proposing to come alone, have written "I trust that it will be convenient to you for I to call upon you. . . . " A sure and easy way of avoiding this blunder is to ask oneself what case the personal pronoun would have been in —would it have been I or me —if it had stood alone. It should remain the same in partnership as it would have been by itself.