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{{dablink|For other senses of this word, see [[bracket (disambiguation)]].}}
:''For technical reasons, ''<tt>:)</tt>'' and some similar combinations redirect here. See [[emoticon]].''
{{Punctuation marks}}

'''Brackets''' are [[punctuation]] marks used in pairs to set apart or interject text within other text. With respect to [[computer science]], the term is sometimes said to only strictly apply to the square or box type.<ref>[http://foldoc.org/index.cgi?query=bracket&action=Search Free Online Dictionary of Computing]</ref>

Types of brackets include '''parentheses''' or '''round brackets'''&nbsp;(&nbsp;), '''box brackets''' or '''square brackets'''&nbsp;[&nbsp;], '''curly brackets''' or '''braces'''&nbsp;{&nbsp;}, and '''angle brackets''' < >.  All these forms may be used according to [[typography|typographical]] conventions that may vary from publication to publication and may vary even more from language to language.  Some typical uses in English texts follow.

== Usage ==  
In addition to referring to the class of all types of brackets, the unqualified word ''bracket'' is most commonly used to refer to a specific type of bracket. In modern American usage this is usually the square bracket, whereas in modern British usage it is usually the parenthesis (round bracket).

In fact, in American usage, parentheses are usually considered separately from other brackets, and calling them ''brackets'' at all is unusual, even though they serve a similar function.  In more formal usage, parenthesis or ''parenthesised'' may refer to the whole bracketed text, not just to the particular punctuation marks used {so all the text in this curly bracket may be said to be parenthesised}.

It must be noted that commas must go outside of the parenthesis, unlike [[quotation mark]]s.

=== Types of brackets ===
====Parentheses ( )====
'''Parentheses''' (the singular is '''''parenthesis''''', with an ''i'') &ndash; sometimes called '''round brackets''', '''curved brackets''', '''oval brackets''', or just '''brackets'''; or, colloquially, '''parens''', or '''fingernails''' &ndash; are used to contain [[parenthesis|parenthetical]] (or optional, additional) material in a sentence that could be removed without destroying the meaning of the main text. 

In formal writing, parentheses may be used to add supplementary information, such as "Sen. Edward Kennedy (D., Massachusetts) spoke at length." They can also indicate shorthand for "either singular or plural" for nouns&mdash;e.g., "the claim(s)".

In literature and informal writing, parenthetical phrases have been used extensively in stream of consciousness literature. Of particular note is the southern American author [[William Faulkner]] (see ''[[Absalom, Absalom!]]'' and the Quentin section of ''[[The Sound and the Fury]]''). In most writing, overuse of parentheses is usually a sign of a badly structured text.  A milder effect may be obtained by using a pair of commas as the delimiter. If the sentence contains commas for other purposes, visual confusion may result.

Historically, parentheses have been used where the [[Slash (punctuation)|solidus]] is modernly used&mdash;that is, in order to depict alternatives, such as "parenthesis)(parentheses". Examples of this usage can be seen in editions of ''[[Fowler's Modern English Usage|Fowler’s]]''.

Parentheses may also be nested (with one set (such as this) inside another set).  This is not commonly used in formal writing (though sometimes other brackets [especially square brackets] will be used for one or more inner set of parentheses [in other words, ''secondary'' {or even ''tertiary''} phrases can be found within the main sentence]).

Any punctuation inside parentheses or other brackets is independent from the rest of the text: "Mrs. Pennyfarthing (What? Yes, that was her name!) was my landlady".  In this usage, the explanatory text in the parentheses is a [[parenthesis]].  (It is most common for the parenthesised text to be within a single sentence, but not uncommon for an entire sentence, or even several sentences, of supplemental material to be in parenthesis.  In this case, even the final full-stop - period - would be within the parentheses. Again, the parenthesis implies that the meaning and flow of the text as a whole would be unchanged were the parenthesised sentences removed.) 

In [[mathematics]], parentheses are used to signify a different precedence of operators. For example, 2&nbsp;+&nbsp;3&nbsp;×&nbsp;4 would be 14, since the multiplication is done before the addition. On the other hand, (2&nbsp;+&nbsp;3)&nbsp;×&nbsp;4 is 20, because the parentheses override normal precedence, causing the addition to be done first. They are also used to set apart the [[parameter|argument]]s to mathematical [[function (mathematics)|function]]s. For example, ''f''(x) is the function ''f'' applied to the [[variable]] x. In the [[coordinate system]], parentheses are used to denote a set of coordinates. For example, (4,7) may represent the point located at 4 on the x-axis and 7 on the y-axis.  Parentheses are also represent [[Interval_(mathematics)|intervals]]. For example, (0,5) is the interval between 0 and 5, non-inclusive. Parentheses can also represent multiplication, as in the instance of 2 (3) = 6. Please note that in mathematic equations, if parentheses are used twice around each other, the inner pair are parentheses and the outer pair are square brackets. Ex: [5-(7+3)]+4=x. Parentheses also represent a [[binomial coefficient]]

[[Image:Brackets.svg|thumb|145px|Various brackets in [[Arial]]]]

==== Box brackets or square brackets [ ] ====

Square brackets are used to enclose explanatory or missing […] material, especially in quoted text. For example, "I appreciate it [the honor], but I must refuse". Or, "the future of [[psionics]] [See definition] is in doubt".  

The bracketed expression [[sic (Latin)|sic]] (Latin for "thus") is used to indicate errors that are "thus in the original"; a bracketed [[ellipsis]] […] is often used to indicate deleted material; bracketed comments are used to indicate when original text has been modified for clarity: "I'd like to thank [several unimportant people] and my parentals [sic] for their love, tolerance […] and ''assistance'' [italics added]". 

In [[mathematics]], square brackets are used in a variety of notations, including standard notations for [[interval (mathematics)|intervals]], [[commutator]]s, the [[Lie bracket]], and the [[Iverson bracket]].

Square brackets are also sometimes used as parentheses within parentheses (secondary parentheses [as mentioned earlier]).

With the [[International Phonetic Alphabet]], square brackets are used to indicate a [[phonetic]] transcription (as opposed to a [[phonemic]] one).

In [[chemistry]], square brackets can also be used to represent the [[concentration]] of a [[chemical substance]], or to denote a [[complex ion]].

In [[architecture]], square brackets can be used to emphasize cool words, such as [metaliving] or [cityscape]. It can also be used to make the layout generally look more cool and [[modern]].

In [[proofreading|proofreading,]] square brackets (called ''move-left symbols'' or ''move right symbols'') are added to the sides of text to indicate changes in indentation:


{| border="1" align="center" width="65%" cellpadding="4"
|-----
| width="15%" |
{| align="left"
'''Move left'''
|}
| width="85%" |
{| align="left"
[To Fate I sue, of other means bereft, the only refuge for the wretched left.
|}
|-----
| width="15%" |
{| align="left"
'''Center'''
|}
| width="85%" |
{| align="left"
]Paradise Lost[
|}
|-----
| width="15%" |
{| align="left"
'''Move up'''
|}
| width="85%" |
{| align="left"
[[Image:Quote_to_be_Moved_Up.svg|330px]]
|}
|}

==== Curly brackets or braces { } ====

Curly brackets (so-called in British English; North American English prefers ''braces'') are sometimes used in prose to indicate a series of equal choices: "Select your animal {goat, sheep, cow, horse} and follow me". They are used in specialized ways in poetry and music (to mark repeats or joined lines). In [[mathematics]] they are used to delimit [[set]]s.

Presumably due to the similarity of the words ''brace'' and ''bracket'' (although they do not share an [[etymology]]), many people casually treat ''brace'' as a [[synonym]] for ''bracket''.  Therefore, when it is necessary to avoid any possibility of confusion, such as in computer programming, it may be best to use the term ''curly bracket'' rather than ''brace''.  However, general usage in North American English favours the latter form.  The  term ''curly braces'' is redundant since no other type of brace exists.  Indian programmers often use the name "flower bracket".

Curly brackets are often used in internet communities and through instant messaging to indicate hugging. {{{{{{{username}}}}}}}

==== Angle brackets or chevrons < > ====

Angle brackets (< >) are often used to enclose highlighted material. Some dictionaries use angle brackets to enclose short excerpts illustrating the usage of words. True angle brackets are not available on a typical computer keyboard, so the "less than" and "greater than" symbols are used instead (&lt;,&nbsp;&gt;). These are often loosely referred to as ''angle brackets'' when used in this way. For example, the symbols &lt;&nbsp;and&nbsp;&gt; are often used to set apart [[URL]]s in text, such as "I found it on Example.com <nowiki><http://www.example.com/></nowiki>". It may also often be found to indicate an [[e-mail]] address, such as "This photo is copyrighted by John Smith <john@smith.com>", and is the computer-readable form for such in [[E-mail#Internet e-mail header|message headers]] as specified by RFC 2822.

Angle brackets are used in physical sciences to denote an average over time or another continuous parameter.  For example, 

:<math>\left\langle V(t)^2 \right\rangle = \lim_{T\to\infty} \frac{1}{T}\int_{-T/2}^{T/2} V(t)^2{\rm{d}}t </math>

In [[linguistics]], angle brackets are used to indicate [[orthography]], as in "The English word {{IPA|/kæt/}} is spelled {{Unicode|〈}}cat{{Unicode|〉}}."

In [[textual criticism]], and hence in many editions of poorly transmitted works, angle brackets denote sections of the text which are illegible or otherwise lost; the editor will often insert his own reconstruction where possible within them.

Single and double angle brackets ({{unicode|&#x27ea;,&nbsp;&#x27eb;}}) or pairs of the appropriate comparison operators (&lt;&lt;,&nbsp;&gt;&gt;) are sometimes used instead of [[guillemets| guillemets ({{unicode|«}}, {{unicode|»}})]] (used as [[quotation mark]]s in many languages) when the proper [[glyph]]s are not available. 

The mathematical or logical symbols for greater-than&nbsp;(&gt;) and less-than&nbsp;(&lt;), when used as such, are not punctuation marks.

[[Chevron]]s are part of standard [[Chinese language|Chinese]], [[Japanese language|Japanese]], and [[Korean language|Korean]] punctuation, where they generally enclose the titles of books: {{Unicode|︿}} and {{Unicode|﹀}} or {{Unicode|︽}} and {{Unicode|︾}} for traditional [[tategaki|vertical printing]], and {{Unicode|〈}} and {{Unicode|〉}} or {{Unicode|《}} and {{Unicode|》}} for [[yokogaki|horizontal]] printing.

In [[comic book]]s, angle brackets are often used to mark dialogue that has notionally been translated from another language.

Angle brackets can also be used to indicate an action or status (eg. <Waves> or <Offline>), particularly in online, real-time text-based discussions (instant messaging, bulletin boards, etc). (Here, asterisks can also be used to signify an action.)

== In computing ==

* Opening and closing '''parentheses''' correspond to [[ASCII]] and [[Unicode]] [[character (computing)|character]]s 40 and 41, or [[hexadecimal|0x]]0028 and 0x0029, respectively.
* For '''square brackets''' corresponding values are 91 and 93, or 0x005B and 0x005D.
* For '''braces''', 123 and 125, or 0x007B and 0x007D.
* True '''angle brackets''' are available in Unicode at code points 0x27e8 and 0x27e9 (for mathematical use), or 0x9001 and 0x9002 (for East Asian languages), or 0x2329 and 0x232A (for "technical" use, canonically equivalent to the CJL code points 0x900x). The less than and greater than symbols can be found in both Unicode and ASCII at code points 60 and 62, or 0x003C and 0x003E.

Also, in many [[computer language]]s:

* "(" and ")"
** are often used to define the syntactic structure of expressions, overriding [[operator precedence]]: <code>a*(b+c)</code> has subexpressions <code>a</code> and <code>b+c</code>, whereas <code>a*b+c</code> has subexpressions <code>a*b</code> and <code>c</code>.
** are used to contain the arguments to functions: <code>substring($val,10,1)</code>.  On the other hand, in [[Lisp programming language|Lisp]] they open and close [[s-expressions]] and therefore function applications: <code>(cons a b)</code>.  In [[Fortran]]-family languages, they are also used for array references.
* "[" and "]"
** are used to refer to array or [[associative array]] elements, and sometimes to define the number of elements in an array: <code>queue[3]</code>. 
** in most [[regular expression]] syntaxes square brackets are used to denote a character class: a series of possible characters to choose from.
* "{" and "}" are used in some languages to define the beginning and ending of [[block (programming)|blocks]] of code. Languages which use this convention are said to belong to the [[curly bracket programming language|curly brace family]] of programming languages.  In some of these languages, they also denote array [[constant]]s.  On the other hand, in the [[Pascal programming language]], "{" and "}" define the beginning and ending of comments. 
* "&lt;" and "&gt;" are used in [[Standard Generalized Markup Language|SGML]] (and its applications and variants such as [[HTML]] and [[XML]]), to enclose code tags: <code>&lt;div&gt;</code>, and in the languages [[Java (programming language)|Java]], C++ and [[C Sharp|C#]] to delimit [[generic programming|generic arguments]] and [[preprocessor]] directives. They are also used as operators for [[redirection (Unix)|redirection]] in Unix. In this context, they are often referred to as '''hoinkies''' (singular '''hoinky''') in order to "avoid confusion with other bracket-type operators" (Bryant and O'Hallaron 2003).

=== Layout styles ===
In normal text an opening bracket is not put at the end of a line, and a closing bracket not at the beginning. However, in computer code this is often done to aid readability. For example, a bracketed list of items separated by semi-colons may be written with the brackets on separate lines, and the items, followed by the semicolon, each on one line.

For example, the [[Cascading Style Sheets|CSS]] code

 H1 { font-weight: bold; font-size: 12pt; line-height: 14pt }

may also be written

 H1 {
   font-weight: bold;
   font-size: 12pt;
   line-height: 14pt
 }

A superfluous semicolon may be added after the last item for uniformity of the item lines.

See [[Indent style]].

== In mathematics ==

In addition to the use of [[Bracket#Parentheses .28 .29|parentheses]] to specify the [[order of operations]], both parentheses and square brackets can also be used to denote an [[interval (mathematics)|interval]].  The notation <nowiki>[a, c)</nowiki> is used to indicate an interval from a to c that is inclusive of a but exclusive of c. That is, <nowiki>[5, 12)</nowiki> would be the set of all real numbers between 5 and 12, including 5 but not 12. The numbers may come as close as they like to 12, including 11.999 and so forth (with any [[finite set|finite]] number of 9s), but 12.0 is not included. In Europe, the notation <nowiki>[5,12[</nowiki> is also used for this.

The endpoint adjoining the square bracket is known as ''closed'', while the endpoint adjoining the parenthesis is known as ''open''. If both types of brackets are the same, the entire interval may be referred to as ''closed'' or ''open'' as appropriate. Whenever [[infinity]] or negative infinity is used as an endpoint, it is always considered ''open'' and adjoined to a parenthesis.

This is used in [[mathematical notation]], and appears in some computer programming languages.  See the article [[Interval (mathematics)]] for a more complete treatment of the subject.

In quantum mechanics, angle brackets are also used as part of [[Paul Dirac|Dirac]]'s formalism, [[bra-ket notation]], to note vectors from the [[dual space]]s of the Bra <A| and the Ket |B>.  Mathematicians will also commonly write <''a'',''b''> for the [[inner product]] of two vectors.  In statistical mechanics, angle brackets denote ensemble or time average.  Angle brackets are used in [[group theory]] to write [[group presentation]]s, and to denote the [[group generators|subgroup generated]] by a collection of elements.

In [[group theory]] and [[ring theory]], square brackets are used to denote the [[commutator]].  In group theory, the commutator <nowiki>[</nowiki>''g'',''h''<nowiki>]</nowiki> is commonly defined as ''g''<sup>&minus;1</sup>''h''<sup>&minus;1</sup>''gh''.  In ring theory, the commutator <nowiki>[</nowiki>''a'',''b''<nowiki>]</nowiki> is defined as ''ab'' &minus; ''ba''.  Furthermore, in ring theory, braces are used to denote the [[commutator|anticommutator]] where {''a'',''b''} is defined as ''ab'' + ''ba''.  The square bracket is also used to denote the [[Lie derivative]], or more generally the Lie bracket in any [[Lie algebra]].

Various notations, like the [[vinculum (symbol)|vinculum]] have a similar effect to brackets in specifying order of operations, or otherwise grouping several characters together for a common purpose.

In the Z [[formal specification]] language, curly braces define a set and angle brackets define a sequence.

==In accounting==

Traditionally in [[Accountancy|accounting]], negative amounts are placed in parentheses.<ref>[http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=/com.ibm.db2.doc.sqlref/bjnrmstr635.htm IBM Information Management Software for z/OS Solutions Information Center]</ref>

== In law ==

Brackets are used in the citation of [[law report]]s to identify whether the report series is sorted by volume number - in which case round brackets are used - or by year - in which case square brackets are used. For example: (1983) 158 CLR 1 or [1998] 2 All ER 153.

== In sports ==

[[Bracket (tournament)|Tournament brackets]], the diagrammatic representation of the series of games played during a tournament usually leading to a single winner, are so named for their resemblance to square brackets.

==History==

The angle bracket was the earliest type to appear in English.  [[Desiderius Erasmus]] coined the term '''''lunula''''' to refer to the rounded parentheses (), recalling the round shape of [[the moon]]. <ref>Truss, Lynne.  ''Eats, Shoots & Leaves'', 2003.  p. 161.  ISBN 1-592-40087-6.</ref>

{{sect-stub}}

==Footnotes==
{{reflist}}

==References==
<div class="references-small">
* {{cite book
  | last = Bryant
  | first = Randal E.
  | coauthors = David O'Hallaron
  | title = Computer Systems: A Programmer's Perspective
  | publisher = Pearson Education, Inc.
  | date = 2003
  | pages = 794
  | id =  ISBN 0-13-034074-X}}
* [[John Lennard|Lennard, John]], ''But I Digress: The Exploitation of Parentheses in English Printed Verse'' (1991) ISBN 0-19-811247-5
* Turnbull et al., ''The Graphics of Communication,'' Holt, New York: 1964 states that what are depicted as square brackets above are called braces and curly brackets are called brackets. This was the terminology in US printing prior to computers.
</div>

== See also ==
* [[Bracket notation]]<nowiki>, a text-based method of tracking changes to a document</nowiki>
* [[Emoticon]]
* [[Japanese typographic symbols]]

[[Category:Punctuation]]
[[Category:Mathematical notation]]
[[Category:Typography]]

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