There are three cases: nominative (for subjects), objective (for objects), and possessive (for possessives)
The man chased the cat. subject He chased the cat.
The cat chased the man. object The cat chased him.
The cat is hiding from the man. object The cat is hiding from him.
That is my pen. possessive (adjective)
That is mine. possessive (pronoun)
Problem areas:
1. Compound Constructions
• My mother and I went to the store. I went to the store.
• She asked my brother and me to be quiet. She asked me to be quiet.
• She bought a chocolate bar for my brother and me. She bought it for me.
2. Comparisons
• My brother is taller than I. My brother is taller than I am.
• The movie scared my brother more than me. The movie scared me.
• His house is more expensive than mine. His house is more expensive than mine is.
3. Who vs. Whom
• Who knows the answer? (Subject) knows the answer.
• Whom do you love? Do you love (object)?
• The doctor helps whoever needs treatment. The doctor helps (subject) needs treatment.
• The doctor helps whomever he treats. The doctor treats (object).