How do you form the possessive of hyphenated noun phrase?

My wife has two married brothers. That means that my father-in-law has two daughters-in-law as well as one son-in-law.

You may notice that the plural changes the form of the base noun, rather than the end of the hyphenated phrase. This should make sense once you realize that the man has three children-in-law, rather than three child-in-laws.

This likely means that the forms "sons-in-law" and "daughters-in-law" sound quite natural to you.


Although the plurality is a property of the base noun, the genetivity is a property of the phrase as a whole. Possessiveness attaches much more loosely than grammatical number.

If only one of your sons-in-law owns this car, then this is your son-in-law's car. If both of your sons-in-law share ownership of this car, then this is your sons-in-law's car. If your daughter-in-law also owns a share of the car, then it's your children-in-law's car.


I'm hoping that "children-in-law's car" is the example that will make the most sense to you. With luck, it'll help you to never again be tempted by your son's car-in-law.

It would be the first one, "My son-in-law's car". When a hyphenated word becomes possessive, the last word will always be where you place the apostrophe. A few more examples:

"I told you, it's no-one's business!"
"I left my watch at my ex-girlfriend's house."

Hope you understand now.

It's your son-in-law's car.