edgood  —  Grammar Tips
The grammatical word object refers to several of the main functions of nouns (and pronouns). A noun can serve as the direct object of a transitive verb, as in John hit the ball. A noun can serve as the object of a preposition, as in Mary went to the party. A noun can serve as an indirect object, as in The professor gave his students a lecture.

If a personal pronoun fulfills any of these grammatical functions as objects, it must appear in the objective case. This is a cardinal rule of grammar—one you must not break.

See verbal object.

© Grammar.com