In English, there are three common uses for the apostrophe [ ‘ ]:
- to show omission (contraction)
- to show possession
- to clarify the meaning or pronunciation of certain non-standard words (typically plurals of abbreviations)
Most folks are familiar with the first two of these uses, or with all three. But most of us also get them wrong now and then. Lynn Truss dedicates at least a full chapter of Eats, Shoots & Leaves just to the apostrophe and common errors involving it.
Omission: When an apostrophe is used to note omission, it’s most commonly when letters are dropped in the formation of a contraction – when do not becomes don’t, for example, or when it is becomes it’s. There are less common contractions – fo’c’sle, o’clock, etc. – but these follow essentially the same rule (forecastle, of the clock). There are also contractions where the apostrophe shows characters dropped at the front of the word – ’tis, ’twas, ’12, etc. (for it is, it was, 2012).
Possession: The use of apostrophes to show possession seems to trip people up frequently. The various rules can get complicated (even the often terse AP Stylebook devotes four full columns to it), but I’ll try to keep it simple, without delving into every special case and exception. There are really two simple general rules that cover the majority of uses, and three special cases that deserve brief mention.
– When a noun is singular and possessive (Mike’s helmet – one Mike, one helmet), add [‘s].
– When a noun is plural and possessive (The teams’ helmets – more than one team, lots of helmets), simply add [ ‘ ]. If the plural noun doesn’t end in s (The children’s helmets), it’s [‘s] again.
The first special case worth knowing about: if the singular noun already ends in s (The boss’ office – one boss, one office) then the general idea is to only add [ ‘ ], not [‘s]. However, this varies in practice, and can often be subject to an individual publisher’s style. Chicago style, for example, recommends always using [‘s] (The boss’s office). If you’re not operating under a specific style, at least do your best to be consistent.
A second special case worth mentioning is similar. In the past some sources have recommended that nouns, especially proper nouns (names) ending in s, z, or x (when they sound near s), such as Marcus, Borax, or Hafez, not take [‘s] but only [ ‘ ]: Marcus’ script, Borax’ claims, Hafez’ problem. Current style seems to be moving away from this, with Chicago explicitly recommending [‘s]: Marcus’s script, Borax’s claims, Hafez’s problem (Chicago 16, 7.16).
A final special case worth mentioning could seem like a subset of the others. It’s what in older editions of style guides is sometimes called ‘the biblical exception.’ This exception notes that when biblical and classical proper nouns form a possessive (Jesus’, Moses’, Sophocles‘, Socrates’) the final [s] should be dropped. I specified older editions here, because current style is moving away from this: “In a departure from earlier practice, Chicago no longer recommends the traditional exception for proper classical names” (Chicago 16, 7.18, 354). Check the specific style you’re using, but chances are that if you’re making the biblical exception, then you’re out of date.
Clarification of unusual plurals or pronunciations : When using a plural form that could be unclear – often of an abbreviation – add [‘s] when forming the plural: CPA’s, MBA’s, IOU’s, ERA’s, and so on. You’ll also rarely encounter a word form that will cause confusion if not helped by an apostrophe. For example, this word: koed. You might be tempted to pronounce it as “code” or “co-ed.” However, if I insert an apostrophe and make it ko’ed you’re much more likely to recognize that it’s pronounced “kay-ode,” as the past tense of ko, short for knocked out. A last form to note here would be dates. While you would shorten 1999 to ’99, most styles will have you refer to the entire decade as either the 1990s (no [ ‘ ], since it’s not possessive) or, in short form, as the ’90s (with only the omission apostrophe). Be careful of unusual cases, like “1990’s greatest hits” (the hits of 1990) or “the 1990s’ greatest hits” (the hits of an entire decade) – which would not only be very unusual in structure, but would also use the apostrophe in what might look like unusual ways.