I vs me

A reader wanted to know why the subjective I in the sentence below is unacceptable:

(1) *The prize will be shared between you and I.

It's an interesting question, and one that touches on a topic we have planned to write. To answer her question adequately, we need to first know the difference between subject and object pronouns.

Subject pronouns are pronouns that take the place of a subject in a sentence. They are typically in front of the verb:

(2) I am hungry.
(3) She runs fast.

In English, the subject pronouns are I, you, he, she, it, they, and we.

Object pronouns are pronouns that take the place of an object in a sentence. Objects are typically behind the verb:

(4) The car nearly hit him.
(5) They saw me.

English uses the object pronouns me, you, him, her, it, them and us.

Next, we look at the word between in sentence (1). Between is a preposition, and that's an important clue. When a pronoun comes after a preposition, it must be in the objective case:

(6) He was angry with me. (not *with I)
(7) The boss thinks highly of her (not *of she)
(8) They were looking for us (not *for we)

It doesn't matter if other intervening elements come between the preposition and the last pronoun. For example:

(9) He was angry with Peter, you and me.
(10) The boss thinks highly of John, you and her.
(11) They were looking for Mary, Jane and us.

So, the correct pronoun in sentence (1) above is me:

(12) The prize will be shared between you and me.

What about you and I? Well, since I is a subject pronoun (as well as you, though the latter is not obvious because its form doesn't change), we use you and I for subjects:

(13) You and I are expected to attend the party. (not *You and me)