Here are the rules of thumb: For most singular nouns, add -’s: For most plural nouns, add only an apostrophe: For plural nouns that do not end in s, add -’s: Style guides vary in their recommendations of what to do to make a singular proper noun that ends in s possessive.

The apostrophe has three uses: to show possession, to show the omission of letters (contractions), and to form plurals of letters, numbers, and symbols. The apostrophe is not used to form plurals of words. The apostrophe is used to show possession, ownership, or belonging, as in the phrases below:

An apostrophe (’) is a punctuation mark used in three primary ways: To indicate possession. To show where letters have been omitted in contractions. To form certain plurals, though this is less common.

The apostrophe ( ’ ) has three uses: contractions, plurals, and possessives. Contractions (e.g., let’s, don’t, couldn’t, it’s, she’s) have a bad reputation. Many argue that they have no place at all in formal writing. You should, of course, observe your publisher’s or instructor’s requirements.