The most common mistakes with grammar often involve seemingly simple things. In English, possession is indicated using an apostrophe and, usually, an added “s.” But maybe because spoken English doesn’t mark the difference between plurals and possessions, such as in “dogs” and “dog’s,” it is common even for experienced writers to make mistakes. This blog reviews some of the basic rules that can help you avoid these easy-to-make errors.

Using the Apostrophe

In English, the apostrophe may be best known for forming a contraction. It marks the spot where a letter has been removed — is not becomes isn’t and was not becomes wasn’t. The apostrophe in the contraction is usually written as a single closing quotation mark — that is, it angles down and to the left, although sometimes it is written straight up and down. (While in English this is mostly a matter of style, in other languages the different single-stroke marks can be used to represent sounds, so getting these right matters.)

The other main use for the apostrophe is to form a possessive. Technically, the possessive is one version of the genitive case; as well as marking the possessive, the genitive can also indicate such things as relationship (“the dog’s mother”) or agency (“the dog’s representative”).

Since adding an “s” without an apostrophe is the most common way of making a plural noun (dogs), it is both important to mark the difference between the plural (dogs) and the possessive (dog’s) in written text.

Forming the Possessive

There is a basic rule for forming the possessive. For a singular noun, add an apostrophe and an “s”; for a plural noun ending in “s,” add only an apostrophe: “the dog’s charming collar” vs. “the other dogs’ groomers were envious.”

This holds even for plural words that are singular in meaning, such as politics and economics.

While some people use only an apostrophe for a single noun ending in “s,” most of the style guides in use today call for an apostrophe plus an “s.” So it would be the boss’s vacation or the class’s schedule (rather than the boss’ vacation or the class’ schedule).

This holds for proper nouns as well, even when the noun ends with an “s.”  So you’d write “I’m going to Carlos’s  house” (singular). If Carlos’s last name was Lincoln and his family invited you over, you’d have to use the plural form Lincolns and write, “We were invited to the Lincolns’ house.”

There’s less agreement on what to do with proper nouns ending with a silent “s” or an “s” pronounced as “z.” Sometimes these are treated the same (“I’d rather have Descartes’s lunch”), while other styles only use an apostrophe (“I’m never taking Socrates’ advice again”).

As always, know what style you’re following, even if it’s your own hybrid form (in which case tell your editors), and stay consistent.

Joint and Separate Possession

What about a situation where more than one person is identified as possessing an object? Here we need to distinguish between joint possession (where ownership is shared) and separate possession (where each individual has ownership of a separate instance of the thing).

For joint possession, say that our dogs went to the Caribbean together: “My dog and your dog’s Caribbean vacation.”

For separate possession (I took my dog to St. Lucia, you took yours to Trinidad): “My dog’s and your dog’s Caribbean vacations.”

Notice that in the first case “vacation” is singular, since only one vacation was taken. In the second case, vacation needs to be plural since two vacations were taken.

The Special Case of It’s / Its

Rules always have exceptions! One of the most glaring ones is that the word it works differently as a contraction and as a possessive pronoun.

The contraction of the noun “it” and “is” is it’s. “It is almost two o’clock” OR “It’s almost two o’clock!”

Its is a possessive pronoun and is used to modify a noun: “The dog enjoyed its vacation very much.”

Similarly, the possessive forms of the personal pronouns hers, his, theirs, ours, yours don’t take apostrophes.

Other Exceptions

Some proper names don’t use apostrophes where you might expect them to — for example, “Diners Club” or the “Ministry of Veterans Affairs.” In these cases, don’t add apostrophes; use the official form.

Other exceptions fall into the “just because” category. Traditionally, “for goodness’ sake,” “for righteousness’ sake,” and a few other similar phrases leave off the final “s.”

In some styles, the possessive of particular proper names don’t take the apostrophe and an “s,” such as Jesus and Moses. Forming the possessive requires only an apostrophe be added: Jesus’ sermons and Moses’ leadership.

Still, exceptions are exceptions — in general, if you follow the rules above you should be able to keep your plurals, possessives, and contractions in good order. For goodness’ sake.

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