Apostrophe

An apostrophe' ( '' or ’ ) is a punctuation mark in languages written in the Latin alphabet. It marks omissions, forms the possessive, and, in special cases, forms plurals.

Usage

An apostrophe is commonly used to indicate omitted letters as in:
- abbreviations, as gov't for government
- contractions, such as can't from cannot and it's from it is.
It is used with an added s to indicate possession, as in Oliver's army, Elizabeth's crown.
It can be used to form a plural for abbreviations and symbols where adding just s rather than ’s would be ambiguous, such as mind your p's and q's. It isn't necessary where there isn't any ambiguity, so CDs not CD's, videos not video's, 1960s not 1960's.

Things to note

The apostrophe in it's marks a contraction of it is or it has. The possessive its has no apostrophe. Many find this confusing. (It might help to remember that there is no apostrophe in any of his, hers, or its.)
Likewise, its role in pluralization of symbols has led to a modern tendency to use the apostrophe incorrectly to form plurals of words, that is plural's of word's, such as the movie title Dating Do's and Don'ts in which the first apostrophe is erroneous.
When the noun is plural and already ends in s, no extra s is added, so pens' lids (where there is more than one pen) rather than pens's lids. If the plural noun doesn't end in s, then add 's as usual: children's hats.
If a name already ends with an s, the extra s is sometimes dropped: Jesus' parables. This is more common in U.S. usage and with classical names (Eros' statue, Herodotus' book). Additionally, many contemporary names that end with -es (a -z sound) will see the extra s dropped by some writers: Charles' car.
Who's means who is or who has. The possessive of who is whose. "The person whose responsibility it is is the member who's oldest."

Tip

To check you've got it right, swap the sentence around so that the part before the apostrophe becomes the last word. If the sense hasn't changed, you've got it right.

Pens' lids becomes lids of the pens.
Boy's hats becomes hats of the boy.
Boys' hats becomes hats of the boys.
Children's hats becomes hats of the children.
Two weeks' notice becomes notice of two weeks.
One week's notice becomes notice of one week.

But childrens' hats becomes hats of the childrens, so must be wrong.

Grocers' apostrophes

Wrongly placed apostrophes are known as Grocers' apostrophes (or sometimes, humorously, as Grocers apostrophe's), due to the frequent occurrence of hand-written signs on their produce, offering potatoe's, cabbage's and such like.

Derivation

The use of the apostrophe to note possession in the English language derived from the Genitive case, but is now considered a Clitic.

Alternative meanings

In computer programming, the "normal" apostrophe ('') ('apostrophe or apostrophe-quote) corresponds to Unicode and ASCII character 39, or U+0027. The (preferred) apostrophe ’ (right single quotation mark or single comma quotation mark) corresponds to Unicode character U+2019.

The difference between the two is great: U+0027 can be used to represent many different characters, such as a punctuation mark, a left single quotation mark, an apostrophe, a prime, etc. U+2019 always represent an apostrophe, or a right single quotation mark.

From the Unicode 2.1 standard:

U+02BC modifier letter apostrophe is preferred where the character is to represent a modifier letter (for example, in transliterations to indicate a glottal stop). In the latter case, it is also referred to as a letter apostrophe.

U+2019 right single quotation mark is preferred where the character is to represent a punctuation mark, as in "We’ve been here before." In the latter case, U+2019 is also referred to as a punctuation apostrophe. [1]

An apostrophe for punctuation should be drawn with a light curl (resembling an upsidedown comma), but U+0027 is nearly always drawn as a straight vertical line, and Unicode actually defines it must be drawn as such. U+2019 has the correct curl.

However, most digital documents use the "normal" apostrophe everywhere. The main reason for this is that on the character ' can be easily typed with any keyboard, whereas typing ’ typically requires a special input method. An additional reason is that there still exist old systems which can only handle ASCII or an 8-bit character encoding such as ISO 8859, which do not include the "correct" apostrophe.

The "normal" apostrophe is also used as a symbol to indicate measurement in feet; the right single quotation mark apostrophe is inappropriate in this context.

External links

Bob's Quick Guide to the Apostrophe, You Idiots (GIF image, from Bob The Angry Flower)
Bob's Quick Guide to Destroying the Apostrophe, You Idiots (GIF image, from the same site)