What to do when you're writing about more than one thing | Plurals in Garbl's Editorial Style Manual

Here's advice from Garbl's Editorial Style Manual on forming plural words to show more than one of the things named:

• For most words, add s: books, guitars. Except when making a plural of single letter, do not add an apostrophe to words or numbers to make them plural.

• Add s to compound words written as single words: cupfuls, handfuls. For compound words that use separate words or link the words with a hyphen, make the most significant word plural: assistant attorneys, attorneys general, daughters-in-law, deputy chiefs of staff.

• Add s to figures: General Motors built the car in the 1940s. The Boeing Co. sold 12 more 767s.

• Don't change the spelling of proper nouns when making them plural. Add es to most proper names ending in es or z: Gonzalezes, Jameses, Joneses, Parkses. Add s to other proper names, including most proper names ending in y even if preceded by a consonant: the Clintons, the Abernathys, not the Abernathies.

• Add es to most words ending in ch, s, sh, ss, x and z: churches, buses, foxes, fuzzes, glasses.

• Change is to es in words ending in is: parentheses, theses.

• Add es to most words ending in o if a consonant comes before o: echoes, heroes. There are exceptions: pianos.

• Words with Latin roots: Change us to i in words ending in us: alumnus, alumni. Change words ending in on to a: phenomenon, phenomena. Add s in most words ending in um: memorandums, referendums but not addenda, curricula, media.

• Avoid using a possessive name as a plural: The free passes are available at four McDonald's restaurants. Not: The free passes are available at four McDonald's.

• Do not use 's when writing about words as words: His speech had too many ifs, ands and buts.

• To avoid confusion, add 's to single letters: Dot your i's. She earned two A's and three B's on her report card. Add s to multiple letters: He knows his ABCs. They have three color TVs.

When providing both the singular and plural forms of a noun, a common style is to put the plural ending in parentheses: truck(s), glass(es). An alternative style is to separate both forms with a slash: truck/trucks, glass/glasses. That style works well if a word must be spelled differently when it becomes a plural, like singular words ending in y (city/cities), singular words ending in f or fe (wife/wives, calf/calves) and odd words like mouse/mice, woman/women. Both styles can produce awkward, confusing sentences, however, and should be avoided unless necessary. Less confusing could be using only the singular form and letting the context show that your statement can apply to more than one thing.

When a number and a noun form a compound modifier (or compound adjective) before a noun, use a singular noun in the phrase and hyphenate the phrase. Drop the hyphens and use plural nouns in other uses: The room measured 6 by 9 feet, but a 6-by-9-foot room. The building has 3,300 square feet of usable space, but a 3,300-square-foot building. The container held 10 gallons, but a 10-gallon container. The type size is 18 points, but 18-point type. Her shift lasted 10 hours, but a 10-hour shift. She was on vacation for three weeks, but a three-week vacation. 

For plurals not covered here, check your preferred dictionary. 

Here's additional advice from my online style manual:

abbreviations and acronyms To form most common plural abbreviations, add an s: ABCs, CDs, chaps., Drs., IOUs, TVs, UFOs. Sometimes, an apostrophe may go before the s: when the abbreviation has internal periods (M.A.'s, M.B.A.'s, Ph.D.'s), when the abbreviation is composed of lowercase letters (pdf's), when the abbreviation is a single letter (A's, S's) and when the abbreviation would be confusing if only the swere added (OWS's instead of OWSs). In the last example, if your readers might misinterpret an abbreviation like OWS's as showing possession, leave out the apostrophe.

capitalization Lowercase common noun elements of names in all plural uses: Democratic and Republican parties, Ackley and Messer streets, 154th and 156th avenues southeast. But don't lowercase the common nouns when the form is not plural: Your sister can catch a bus on First or Third Avenue.

collective nouns Collective nouns name a group or collection of people, places, things, ideas, actions or qualities, including board, class, committee, crowd, family, group, herd, jury, panel, public, orchestra, staff, team. Nouns that show a unit take singular verbs and pronouns: The board is electing its committee chairs. The crowd is eager to march. To stress individuals in a group, use members of: Staff members answered questions. Some members of the panel left before lunch. 

Some nouns are both singular and plural in meaning, including corps, chassis, deer, fat, fish, grease, moose, oil, public, sediment, sheep, soil, water and waste. The use of a singular or plural verb in a particular sentence conveys the meaning. Because these words are already plural, avoid adding s or esto make them plural: Scientists studied sediment from Charger Bay. The geologist took samples of soil from the site. When mentioning various types or species, however, plural spellings may be used:Scientists studied Fox Lake and Lake Roosevelt sediments. The site contained both glacial and sandy soils.

Follow the rules of subject-verb agreement when using the proper names of athletic teams and musical bands or groups: The Seattle Mariners are on the road. The Seattle Storm is an event sponsor. The Beatles were wonderful at the old Seattle Center Coliseum and so were the Rolling Stones. The Who is still terrific.

possessives 

• Use only an apostrophe for singular proper names ending in s: Drakes' decision. And add only an apostrophe to plural proper names ending in s: the Parkses' home.

• Add 's to plural nouns not ending is s: children's passes, men's bike, women's rights, women's room.

• Add only an apostrophe to plural nouns ending in s: the girls' books, boys' bike, plants' supervisors, families' cars.

• When a plural noun is possessive but each person "owns" only one item, the item should also be listed in plural form. To confirm correctness, rephrase the possessive relationship as an of phrase:the children's brains or the brains of the children; the teachers' hands or the hands of the teachers.

• Follow the rule above (and its test for correctness) when using plural nouns and possessive pronouns: The children became upset when their mothers left the room or the mothers of the children. Gerry and Lena took their dogs for a walk or the dogs of Gerry and Lena.

• When writing about a family in the plural, add s and then an apostrophe: the Abernathys' Christmas greeting (but Bob Abernathy's Christmas greeting). See plurals above.

• Add only an apostrophe to nouns plural in form, singular in meaning: mathematics' rules, United States' wealth.

• Treat nouns that are the same in singular and plural as plurals, even if the meaning is singular:the two deer's tracks. See collective nouns above.