The Editor's Manual
Grammar, usage, punctuation, and style resource for editors, writers, and learners of the English language.
Avoid using an apostrophe before the “s” in a plural, unless not using one would result in confusion (e.g., two “i’s” in “iridescent”).
Form the possessive of a name ending in “s” by adding an apostrophe and another “s” or by simply adding an apostrophe. The possessive of a plural name takes an apostrophe after the final “s” (“the Harrises’ home”).
Regular plurals are formed by adding “-s,” “-es,” or “-ies” to the singular (“girls,” “viruses,” “duties”). Irregular plurals also often follow a pattern, originating sometimes in the parent language or rules of older forms of English (e.g., “children,” “criteria,” “mice”).
Data can be a plural noun (“the data are”) or a singular mass noun (“the data is”). As a mass noun, it is used much like the word “information.”
Use an apostrophe to indicate possession (“the woman’s hat”) or the omission of letters (“wouldn’t”, “singin’”). Only rarely is an apostrophe used to form a plural (“p’s and q’s”).
Count nouns have singular and plural forms (e.g., star/stars). Mass nouns are thought of in terms of quantity rather than number of units, and have no distinct singular and plural forms (e.g., milk, excitement, oxygen).
The plural of an abbreviation is formed by adding an “s” (URLs, DVDs). Avoid inserting an apostrophe to form the plural. Abbreviated SI units do not have a separate plural form (1 cm and 10 cm). Abbreviated social titles such as “Mr.” and “Mrs.” have nonstandard plurals.
Provide the full form of an abbreviation at first use. Abbreviations that are acronyms or initialisms generally use all capital letters, while contractions and abbreviated Latin terms often contain lowercase letters. Use of “a” or “an” before an abbreviation depends upon how the abbreviation is pronounced.