Object Pronoun

A pronoun is a word that takes a place of a noun. There are three types of pronouns: subject pronouns, object pronouns and prossessive pronouns.

• Subject Pronouns: I, you, he, she, it, we and they. 
• Object Pronouns: me, you, him, her, it, us and them. 
• Prossessive pronouns include mine, yours, his, hers, its, ours and theirs.

Subject pronouns are used when the pronoun is the subject of the sentence. Also, they can be used to rename the subject when they follow to be verbs such as is, are, was, were, am, and will be. However, in spoken English, most people tend to put object pronouns after to be verbs. Many English teachers support (or at least have given in to) this distinction between written and spoken English.

• Example: It could have been her.
• Better: It cound have been she.

Besides being subject pronouns, object pronouns are used everywhere else  (direct object, indirect object, object of the preposition).

To decide whether to use the subject or object pronoun after the words than or as, mentally complete the sentence.

• Martha is as smart as he / him.
• Martha is as smart as he (is). ----------------------------------- Correct
• Martha is as smart as him. -------------------------------------- Incorrect

• John is taller than I / me.
• John is taller than I (am). --------------------------------------- Correct
• John is taller than me. ------------------------------------------- Incorrect

• Mr. Smith would rather talk to her than I / me.
• Mr. Smith would rather talk to her than I (would). ---------- Correct
• Mr. Smith would rather talk to her than (to) me. ------------- Correct

The last example is correct using both I and me, but has different meanings. With I (Subject Pronoun) used, the sentence is saying who prefers to talk to her, Mr. Smith or I. With me (Object Pronoun) used, the sentence is saying to whom Mr. Smith prefers to talk, her or me.

Reference:

• GrammarBook.com