Pronoun Case

Pronouns (and nouns) in English display "case" according to their function in the sentence. Their function can be:

The following table shows the different forms for pronouns depending on case.

      subjective
case
objective
case
possessive
case
personal pronouns singular 1st I me mine
2nd you you yours
3rd he
she
it
him
her
it
his
hers
its
plural 1st we us ours
2nd you you yours
3rd they them theirs
relative / interrogative pronouns who whom whose
whoever whomever  
which, that, what which, that, what  
indefinite pronouns everybody everybody everybody's

A problem of case:
Mary and I or Mary and me?

  1. Mary and I are happy to be here today. (NOT Mary and me)
  2. Ati sent the letter to Mary and me. (NOT Mary and I)

In 1, Mary and I are subjects, which is why the pronoun takes the subjective case ("I"). In 2, Mary and I are objects, which is why the pronoun takes the objective case ("me"). An easy way to check the correct case is to try the sentence without Mary. Would you say "I am happy to be here" or "Me am happy to be here"? Would you say "Ati sent the letter to me" or "Ati sent the letter to I"?