What are the rules for forming possessive nouns with compound nouns?

When forming possessive nouns with compound nouns, there are a few rules to follow.

1. If the compound noun is singular and consists of two or more words, add an apostrophe and an "s" ('s) to the last word of the compound noun. For example, "my sister-in-law's car" or "the president's speech."

2. If the compound noun is plural and ends in "s," simply add an apostrophe after the "s." For example, "the students' books" or "the dogs' toys."

3. If the compound noun is plural and does not end in "s," add an apostrophe and an "s" ('s) to the last word of the compound noun. For example, "the children's toys" or "the men's jackets."

4. If the compound noun is joint possession, meaning that the possession is shared by two or more nouns, add an apostrophe and an "s" ('s) to the last noun in the compound. For example, "John and Mary's house" or "the company's employees."

5. If the compound noun is separate possession, meaning that each noun possesses something individually, add an apostrophe and an "s" ('s) to each noun in the compound. For example, "Tom's and Jerry's cars" or "the girls' and boys' toys."

It is important to note that when the compound noun is a proper noun, such as a name, the same rules apply. However, if the proper noun already ends in "s," you can choose to either add an apostrophe and an "s" ('s) or just an apostrophe after the "s" to form the possessive noun. For example, "Charles's car" or "Charles' car."

By following these rules, you can correctly form possessive nouns with compound nouns.