The apostrophe ( ’ , ' ) is a punctuation mark used in languages that write with the Latin alphabet and some other alphabets. In English, the apostrophe has two main uses:

It shows possession, such as in "the cat's toy" or "Sarah's book." It is also used in a few special cases to form plurals, like in "p's and q's" or "Oakland A's." The apostrophe can also act as a single quotation mark. Sometimes, it is used informally in place of other symbols, such as the prime symbol, to represent units like feet or minutes of arc.

The word "apostrophe" comes from the Greek term ἡ ἀπόστροφος [προσῳδία], meaning "turning away or elision." This term passed through Latin and French before becoming the word we use today.

Usage in English

The apostrophe was first used by Pietro Bembo in his edition of De Aetna in 1496. It was introduced into English in the 16th century, following French practices.

Geoffroy Tory introduced the apostrophe in 1529. It was used to replace a vowel letter when a sound was left out, such as in l'heure instead of la heure. It was also used to replace a final e (which was still spoken at the time) when it was left out before a vowel, as in un' heure. Modern French spelling has changed back to une heure.

From the 16th century, English followed French practices and used the apostrophe when a vowel was left out. This happened either because a sound was skipped (as in I'm for I am) or because a letter no longer made a sound (as in lov'd for loved). English spelling kept many letter endings that were no longer pronounced, such as -est, -eth, -es, -ed for verbs and -es for nouns. These endings marked plurals or possessives (called genitives). An apostrophe followed by s was often used to show a plural, as noted in The Oxford Companion to the English Language.

Elision, or leaving out sounds, is still used today. However, rules for possessive and plural forms have changed. By the 18th century, an apostrophe with an s was used for all possessive singular forms, even when the letter e was not left out (as in the gate's height). This was seen as representing the loss of an e from Old English endings, not from modern spellings.

Plural possessives sometimes had the same spelling as singular possessives, causing confusion. To fix this, an apostrophe was added after the plural s (as in girls' dresses). This change became widely accepted by the mid-19th century. Plurals not ending in -s keep the -s marker, such as children's toys or men's toilet, to avoid confusion.

The apostrophe is used in English to show the possessive case, which is called the genitive in older language rules. This case shows relationships other than ownership. For example, the school's headmaster does not mean the school owns the headmaster. Merriam-Webster's Dictionary of English Usage notes that only 40% of possessive forms show actual ownership. Modern rules distinguish between singular possessives (Bernadette's, flower's), simple plurals (Bernadettes, flowers), and plural possessives (Bernadettes', flowers'). For example, glass's is the singular possessive of glass, while glasses' is the plural possessive.

Possessive personal pronouns like ours, yours, his, hers, its, theirs, and whose do not use an apostrophe, even if they end with s. Other pronouns, singular nouns not ending in s, and plural nouns not ending in s use 's for the possessive, such as someone's, a cat's toys, and women's. Plural nouns already ending in s use only an apostrophe for the possessive, like three cats' toys.

For most singular nouns, 's is added, such as the cat's whiskers. If a singular noun ends with an s sound (spelled with -s, -se, etc.), rules vary on whether to use 's or just an apostrophe. Acronyms like TV follow the same rules as singular nouns: the TV's picture quality.

When a noun is a normal plural (with an added s), no extra s is added for the possessive. For example, the neighbours' garden is standard, not the neighbours's garden. If the plural is not formed by adding s, an s is added after the apostrophe, such as children's hats or some people's eyes.

Some nouns have plurals not ending in s but still end with an s or z sound, like mice, dice, and pence. Their possessives are formed by adding 's, such as seven titmice's tails or the dice's last fall. These are often rephrased for clarity.

Compound nouns use 's for possessives, such as *the Attorney-General's

Non-English use

In many languages, especially European languages, the apostrophe is used to show when one or more sounds are left out, as in English.

• In Albanian, the apostrophe is used to show that a vowel has been left out in words, especially in different forms of verbs and personal pronouns. For example, t'i means "them" (from të + i), and m'i mori means "he took them" (from më + i mori). It is also used in some forms of possessive pronouns, such as s'ëmës (from së ëmës).
• In Afrikaans, like Dutch, the apostrophe is used to show that letters are left out. The most common use is in the word 'n, which is a shortened form of een meaning "one." When 'n starts a sentence, the next word is capitalized, as in 'n Boom is groen ("A tree is green"). The apostrophe is also used for plurals and diminutives when a word ends with a long vowel, such as foto's, taxi's, Lulu's, and Lulu'tjie.
• In Catalan, French, Italian, Ligurian, and Occitan, the apostrophe is used when a word ending with a vowel or a silent h is followed by another word that starts with a vowel. For example, L'Aquila (The Eagle) and L'Alpe d'Huez (Alpe d'Huez). In French, words like qu'il (instead of que il) and c'est (instead of ce est) use the apostrophe. Some surnames, like d’Alembert and D'Angelo, also use the apostrophe. In French, possessive adjectives like ma (my) change to mon (my) before masculine nouns, such as mon église (my church). In Quebec, a law called Bill 101 requires proper names to avoid using apostrophes if they are not used in standard French, so names like Tim Hortons (originally Tim Horton's) had to remove the apostrophe.
• In Danish, the apostrophe sometimes appears in advertisements, such as Ta' mig med ("Take me with"), even though the correct spelling is Tag mig med. The apostrophe is not used for possessive forms unless the base word already ends with s, x, or z, such as Esajas' bog ("The Book of Esajas").
• In Dutch, like Afrikaans, the apostrophe is used to show omitted letters. For example, een becomes 'n and het becomes 't. When these shortened forms start a sentence, the next word is capitalized. The apostrophe is also used in phrases like 's morgens ("at morning") and in place names like 's-Hertogenbosch. It is used for plurals ending with long vowels, such as foto's and taxi's, and for possessive names like Anna's and Otto's.
• In Esperanto, the apostrophe is used mainly in poetry and songs to show omitted letters, such as l' (from la) and kor' (from koro). Some phrases like dank' (from danko) and del' (from de la) use the apostrophe. Hyphens are used for compound words, such as D-ro (from doktoro).
• In Finnish, the apostrophe shows that a k between similar vowels is left out in certain word forms. For example, raaka ("raw") becomes raa'at in the plural. The apostrophe helps show that the vowels on either side belong to different syllables.
• In Galician, the apostrophe is used in contractions when the second word is a proper noun, such as d'A Esmorga ("of A Esmorga"). It is also used for spoken elisions and to join names of businesses, like O'Pote ("The Pot").
• In Ganda, when a word ending with a vowel is followed by a word starting with a vowel, the final vowel is left out, and the next vowel is lengthened. For example, taata w'abaana ("the father of the children") shows that wa becomes w'. However, if the first word has more than one syllable, the vowel is still written, such as omusajja oyo ("this man").
• In German, the apostrophe is used mainly to show omitted letters. It is not used for plurals or most possessive forms, except when a name ends with an s sound, like Max' Vater ("Max's father"). The use of apostrophes for possession is not widely accepted and is often considered incorrect.
• In Ancient Greek, apostrophes are used to show when a vowel is left out, such as d'állos (from dè állos). This is different from other Greek writing styles.
• In Hebrew, the apostrophe (called geresh) is used for abbreviations and acronyms. For example, פרופ׳ stands for professor. It is also used to show when a sound is left out, like אנ׳לא (short for אני לא, "I am not").
• In Irish, the past tense of verbs is formed with specific rules, but the text provided ends here.

Typographic form

The shape of the apostrophe began in handwritten manuscripts, where it was drawn as a small point with a tail that curved downward and to the right. This is the same shape used in modern punctuation (’), which is also called the typeset apostrophe, typographic apostrophe, or curly apostrophe. It is similar to the right single quotation mark. Later, some typefaces, such as sans-serif fonts, changed the apostrophe’s shape to be more geometric or simpler, but they still kept the same direction as a closing quotation mark.

When typewriters were invented, a new symbol called the "neutral" or "straight" quotation mark (’) was created. This symbol, known as the typewriter apostrophe or ASCII apostrophe, was used to represent several different symbols with one key: the apostrophe, both the opening and closing single quotation marks, single primes, and on some typewriters, even the exclamation point (by combining a period and backspacing). This same approach was used for double quotation marks ("). These changes were later included in computer keyboards and the ASCII character set.

Informal use in measurement and mathematics

The symbol used to show a foot of length, depth, or height is ′ (called a prime), and the symbol for an inch is ″ (called a double prime). For example, the notation 5′ 7″ means 5 feet and 7 inches. The same symbols are also used in measuring angles. The prime symbol represents a minute of arc, which is 1/60 of a degree, and the double prime symbol represents a second of arc. For example, 17°54′32″ means 17 degrees, 54 minutes, and 32 seconds. In mathematics, the prime symbol is often used to create new names for similar items without using subscripts. For example, x′ usually refers to something connected to or based on x. The symbols on a typewriter, such as the apostrophe (′) and double quote (″), look similar to the prime and double prime symbols. However, using these typewriter characters is not recommended in situations where clear writing is important. This is because typewriter characters may be automatically changed into standard punctuation marks, like apostrophes and quotation marks, which are not the same as the symbols meant to be used.

Unicode

The Unicode Standard (version 13.0) explains that three characters represent an apostrophe:

• U+0027 ' APOSTROPHE: This is the standard typewriter or ASCII apostrophe.

• U+2019 ’ RIGHT SINGLE QUOTATION MARK: This is preferred when the apostrophe is used as punctuation, such as in contractions like "we’ve." It is also called a punctuation apostrophe. In Unicode 2.1, this character was combined with the closing single quote to fix issues in code pages from Windows and Macintosh. This change can make searching for text harder because quotes and apostrophes may look the same without context.

• U+02BC ʼ MODIFIER LETTER APOSTROPHE: This is used when the apostrophe acts as a modifier letter, such as in transliterations to show sounds like the Arabic glottal stop (hamza) or the Cyrillic "soft sign." It is also called a letter apostrophe. This character is used in some languages, like Breton (e.g., "cʼh"), where it forms part of a three-letter combination. ICANN considers this the correct character for the Ukrainian apostrophe in IDNs. It appears the same as U+2019 in Unicode charts, but the standard warns that it should not be assumed to be used in any specific language.

Other Unicode characters related to apostrophes or similar marks include:

• U+0027 ' APOSTROPHE
• U+0060 ` GRAVE ACCENT
• U+00B4 ´ ACUTE ACCENT
• U+02B9 ʹ MODIFIER LETTER PRIME (used for Hawaiian ʻokina and transliterations of Arabic and Hebrew ʻayn)
• U+02BB ʻ MODIFIER LETTER TURNED COMMA
• U+02BC ʼ MODIFIER LETTER APOSTROPHE
• U+02BD ʽ MODIFIER LETTER REVERSED COMMA
• U+02BE ʾ MODIFIER LETTER RIGHT HALF RING (used for Arabic hamza and Hebrew alef)
• U+02BF ʿ MODIFIER LETTER LEFT HALF RING (used for Arabic and Hebrew ʿayin)
• U+02C8 ˈ MODIFIER LETTER VERTICAL LINE (used for stress or dynamic accents)
• U+02CA ˊ MODIFIER LETTER ACUTE ACCENT
• U+02EE ˮ MODIFIER LETTER DOUBLE APOSTROPHE (used for glottal stop in Nenets)
• U+0301 ◌́ COMBINING ACUTE ACCENT
• U+0313 ◌̓ COMBINING COMMA ABOVE (also called combining Greek psili)
• U+0314 ◌̔ COMBINING REVERSED COMMA ABOVE (also called combining Greek dasia)
• U+0315 ◌̕ COMBINING COMMA ABOVE RIGHT
• U+0341 ◌́ COMBINING ACUTE TONE MARK
• U+0343 ◌̓ COMBINING GREEK KORONIS (same as U+0313)
• U+0374 ◌̑ GREEK NUMERAL SIGN (also called Greek dexia keraia)
• U+0384 ΄ GREEK TONOS
• U+055A ՚ ARMENIAN APOSTROPHE
• U+059C ֜ HEBREW ACCENT GERESH
• U+059D ֝ HEBREW ACCENT GERESH MUQDAM
• U+05F3 ׳ HEBREW PUNCTUATION GERESH
• U+1FBD ᾽ GREEK KORONIS
• U+1FBF ᾿ GREEK PSILI
• U+2018 ‘ LEFT SINGLE QUOTATION MARK (also called turned comma, used to mark omitted letters)
• U+2019 ’ RIGHT SINGLE QUOTATION MARK
• U+201B ‛ SINGLE HIGH-REVERSED-9 QUOTATION MARK
• U+2032 ′ PRIME
• U+2035 ‵ REVERSED PRIME
• U+A78B ꘾ LATIN CAPITAL LETTER SALTILLO (used in Mexican languages)
• U+A78C ꞌ LATIN SMALL LETTER SALTILLO
• U+FF07 ＇ FULLWIDTH APOSTROPHE (a wide version of the typewriter apostrophe).

Computing

Unicode is the main way computers encode characters today. However, Unicode and older computer systems still use some methods from the past. Also, the limited number of characters on computer keyboards has led to practical changes. These details are explained below.

The typewriter apostrophe, ' , was used on early computer keyboards. In the ASCII system (a 7-bit encoding), this character is at code 0x27 (39). In ASCII, it can represent a left or right single quotation mark, an apostrophe, a vertical line, a prime symbol, or an acute accent. Unicode, which includes all ASCII characters, uses U+0027 for the apostrophe. Before 1985, some computer systems displayed the ASCII apostrophe as a punctuation mark and the backtick ( ` , code 0x60, 96) as a left quotation mark. This made text look more like printed material: “I can't'' would appear as “I can´t´´ on these systems. This style is still visible in old documents and used in the TeX typesetting system.

Support for the punctuation apostrophe ( ’ ) appeared in some 8-bit systems, like the Mac Roman encoding (1984) and Microsoft Windows' CP1252. These systems used the same code for a closing quotation mark. ISO 8859-1 does not include this character. CP1252 places the punctuation apostrophe at 0x92. Because Microsoft software often changes ASCII apostrophes to this value, other programs have adopted it as a standard. HTML5 uses this code to represent the punctuation apostrophe. Earlier browsers sometimes displayed a question mark instead, making web pages from Microsoft software hard to read. Unicode uses U+2019 for the punctuation apostrophe, which is the most common form.

The punctuation apostrophe ( ’ ) is common in printed materials but hard to type on most keyboards, as it has no dedicated key. Most people use the typewriter apostrophe ( ' ) instead. Word processors often change typewriter apostrophes into punctuation apostrophes automatically, which is why punctuation apostrophes appear in many documents. XML and HTML5 use ' to represent the ASCII apostrophe.

To help users type punctuation apostrophes, some software changes typewriter apostrophes into punctuation ones during typing, along with quotation marks. This is called the "smart quotes" feature. Apostrophes and quotes that are not changed are called "dumb quotes."

Smart quotes sometimes cause errors. For example, they might change a leading apostrophe into an opening quotation mark (e.g., ‘29 instead of ’29 for years like 1929 or 2029). They might also incorrectly use an apostrophe instead of a prime symbol (e.g., 49° 53 ’ 08″ instead of 49° 53 ′ 08″).

In Microsoft Word, users can disable smart quotes by adjusting settings or using the Undo function (Control-Z) to revert apostrophes. Holding the Control key while typing two apostrophes creates a single punctuation apostrophe.

Some programming languages, like Pascal, use the ASCII apostrophe to mark the start and end of text strings. In languages like JavaScript, Python, and others, either apostrophes or double quotes can be used. Strings marked with apostrophes are often called "single quoted." In Perl, PHP, and some shell languages, single-quoted strings are treated as raw text, while double-quoted strings include variable values.

The C programming language (and languages like C++, Java, and C#) uses apostrophes to mark single-character values. In C++, apostrophes can also be used as optional digit separators in numbers. In Visual Basic, an apostrophe marks the start of a comment. In Lisp, an apostrophe is shorthand for a quote command. In Rust, apostrophes can also start an explicit lifetime.