When an item belongs to more than one person, an apostrophe is used to show plural possession. What's the difference between boy's and boys'? Or fox's and foxes'? "Boy" and "fox" are singular nouns, so "boy's" would be the possessive for one boy and "fox's" would be the possessive for a single fox. By contrast, "boys" and "foxes" are plural nouns and these are their plurals: boys' and foxes'. Can you spot the difference between singular and plural possessives? A den inhabited by one fox would be a fox's den, while one with multiple inhabitants would be the foxes' den. As you know, making a singular noun possessive requires the addition of an apostrophe plus an -s. And as you might have spotted, making a plural noun possessive can be as simple as adding an apostrophe at the end of the word.
But is that really all there is to it? Which of these two would be correct: children's or childrens'? If you choose "children's", you would be right. Although the word does not end in an -s, "children" is a plural noun. In this case, the word follows the same rule as a singular noun and takes an apostrophe plus an -s. So the following are correct: geese's, mice's, sheep's, feet's, teeth's, etc. The geese's feathers were coated in oil; the mice's fur was white; the sheep's field was full of lush grass; her feet's odour was atrocious; his teeth's brilliance was blinding.
Practise your apostrophe skills by playing the following quiz!