Nouns are one of eight classes of words or parts of speech in the English language. Broadly, a noun is the name of a person, place or thing, or it can be an abstract notion such as “information” or “wish”. When we want to indicate possession or ownership of something, we use an apostrophe, such as in Mary’s house or the book’s cover. The first noun in these cases is the possessive noun.
For singular common nouns, an apostrophe and an “s” is added to the noun to make it a possessive noun. Examples include the carpenter’s toolbox, the cat’s basket, the river’s water quality, the scarf’s colors, the government’s policies, the town’s population and for argument’s sake. If a noun already ends in “s”, an apostrophe s is usually added just the same, such as the boss’s office and the atlas’s index.
Plural nouns simply take an apostrophe at the end of the word without adding an “s”, to make them possessive. Examples include the judges’ comments, the nurses’ uniforms and the governments’ budgets. Where a plural noun doesn’t end in “s”, an apostrophe and an “s” are added to these words to make them possessive, such as children’s toys, people’s preference and mice’s nests.
For personal names, an apostrophe and an “s” are added, as in Frank’s articles, Janet’s husband, Paul’s sister and Fido’s bone. A problem arises where the name ends in “s”. There are no hard and fast rules, and usage varies. Some people prefer James’s car while others like James’ car. Similarly, with a two-syllable name ending in “s”, such as Dickens, we can use either Dickens’ novels or Dickens’s novels. When it comes to Francis’ car versus Francis’s car, the preference might be for the former, as the latter has a lot of “s” sounds together. For this reason, we would probably say or write Francis’ scooter rather than Francis’s scooter (four “s” sounds in a row). Thus possible rules are to always add just an apostrophe, or to only do this when the noun is more than one syllable, or when it has two successive “s” sounds at end, or always add an apostrophe and an “s”.
With the names of institutions and placenames, the move seems to be away from treating these nouns as possessive, although this varies between countries. Businesses that used to use an apostrophe are now less likely to, for example, Harrods (UK), or they might leave off the “s” altogether, such as Myer (Australia). For cases such as the Libraries Board, an apostrophe would now be rare. A term such as writers’ group is perhaps becoming writers group. Here, the plural word is more like an adjective than a possessive noun. Similarly with placenames, fewer apostrophes are used and we tend to prefer Smiths Beach to Smith’s Beach. Some jurisdictions use no or very few apostrophes in placenames, such as the United States and Australia. Others, including the United Kingdom and Canada, have retained an apostrophe in many cases.
Hyphenated words take an apostrophe at the end of the word, such as mother-in-law’s birthday and editor-in-chief’s duties. Compound titles also do this, for example, the Opposition Leader’s speech and the School of Medicine’s student intake.
Where several people are involved in the possession of something, use of apostrophes depends on whether the ownership is joint or separate. If it’s joint, only the second-mentioned party would take an apostrophe, such as John and Betty’s house or Bill and Ben’s books. However, if ownership is separate, both or all parties would have an apostrophe, for example, Bill’s and Ben’s books. Note that if any party is referred to by a pronoun, the possessive case in used for both or all. For example, we would say Bill’s and his books, regardless of whether Bill and Ben own the book jointly or separately. Also note that where ambiguity could result, the possessive would be used for both parties. Consider the following. Jack and Jill’s children were reported missing. This could mean that Jack was missing, along with Jill’s children, perhaps from another marriage. Here it might be better to refer to Jack’s and Jill’s children.
For double possessives, both people take an apostrophe. Examples include Peter’s friend’s car, her boyfriend’s father’s job, St Paul’s Cathedral’s history and Sue’s partner’s family. An alternative to, say, Janet’s husband would be the husband of Janet’s (not Janet). The latter is often called a double possessive, although it is not usually the preferred option. A double possessive in this format shouldn’t be used for inanimate objects. Here we would say, for example, a friend of the gallery but not a friend of the gallery’s.
A common error is to put an apostrophe in a plural noun where no possession is present, for example, fresh apple’s here, used car’s, and there were two clock’s on the mantelpiece. Also, where there is no actual ownership, an apostrophe isn’t usually used, such as visitors book, girls school and proofreaders marks, although usage can vary between countries.
In summary, the general rule for indicating possession is to add an apostrophe and an “s” at the end of the word. For plural nouns ending in “s”, just an apostrophe is added after the “s”. Where a personal name ends in “s”, sometimes an apostrophe and an “s” is added and sometimes just an apostrophe. The use of apostrophes where several people are involved depends on the circumstances.