What are the rules for using possessive nouns and pronouns in a sentence?

The rules for using possessive nouns and pronouns in a sentence are as follows:

1. Possessive Nouns:
- To show ownership or possession of something, add an apostrophe (') and an "s" ('s) to the end of a singular noun.
Example: The dog's bone is buried in the backyard.
- If a plural noun already ends in "s," only an apostrophe (') is added to indicate possession.
Example: The students' books are on the shelf.
- For plural nouns that do not end in "s," add an apostrophe (') and an "s" ('s) to indicate possession.
Example: The children's toys are scattered on the floor.

2. Possessive Pronouns:
- Possessive pronouns are used to show ownership without the need for an apostrophe.
Example: The book is mine. (Not "The book is my's.")
- The most common possessive pronouns are: mine, yours, his, hers, its, ours, and theirs.
Example: The car is theirs.

3. Joint Possession:
- When two or more people share ownership of something, only the last noun takes the possessive form.
Example: John and Mary's house is beautiful. (Not "John's and Mary's house is beautiful.")

4. Indefinite Pronouns:
- When using indefinite pronouns like someone, anyone, nobody, everybody, etc., add an apostrophe (') and an "s" ('s) to indicate possession.
Example: Somebody's bag is left behind.

5. Compound Nouns:
- For compound nouns, only the last word takes the possessive form.
Example: My sister-in-law's car is parked outside.

6. Proper Nouns:
- Proper nouns, such as names, already indicate possession, so they do not require an apostrophe or an "s" to show ownership.
Example: This is Sarah's house.

Remember to follow these rules to ensure correct usage of possessive nouns and pronouns in your sentences.