3. Function in a sentence
Nouns have certain functions (jobs) in a sentence, for example:
• subject of verb: Doctors work hard.
• object of verb: He likes coffee.
• subject and object of verb: Teachers teach students.
But the subject or object of a sentence is not always a noun. It could be a pronoun or a phrase. In the sentence "My doctor works hard", the noun is "doctor" but the subject is "My doctor".