Grammar: Brackets

 

Two kinds of brackets appear in standard English: round brackets ( ) and square brackets [ ]. Angular brackets < > are used by scholars to indicate
missing or faulty texts and by computer programmers to indicate fields or tags. Brace brackets { } are used only by mathematicians.

 

Round Brackets (  )

The main purpose of round brackets (also called parentheses, meaning ‘an insertion besides’) is, as in this sentence, to enclose supplementary
information that would otherwise interrupt the flow. Although commas can be used for the same purpose, they generally enclose information that is
either short or closely related to the rest of the sentence –

      Alaska, the 49th state of the United States of America, comprises some
      590,000 square miles and 624,000 people.

For more divergent or lengthy information, brackets are preferred –

      Alaska (purchased from Russia in 1867 and granted statehood in 1959)
      comprises some 590,000 square miles and 624,000 people.

When the brackets enclose a complete sentence, the full stop must be placed inside the brackets, not outside –

      Alaska is the largest but least populated state of the USA, comprising
      some 590,000 square miles and 624,000 people. Between the 1940s and
      the 1960s, the economy was generated more by defence than mining.
      (Gold and copper were found in the late nineteenth century, while the
      vast oil reserves were not discovered until 1968.) Since then...

Such independent (sentence-like) clauses are often treated as part of the larger sentence, although this is not universally approved –

      Alaska is the largest but least populated state of the USA, comprising
      some 590,000 square miles and 624,000 people. Between the 1940s and
      the 1960s, the economy was generated more by defence than mining (gold
      and copper reserves were found in the late nineteenth century, while the
      vast oil reserves were not discovered until 1968). Since then...

The remaining uses of round brackets are to enclose the years of people’s births and deaths –

      J. S. Bach (16851750) has been called the musician's composer

to enclose sources of information in some referencing systems

      For Hobbes, it is a point of logic rather than prescription that the sovereign
      is above the law (Smith, 2011)

to indicate alternative singular and plural noun forms –

      Please ensure that your book(s) are scanned at the desk before you leave
      the library

(Note that the auxiliary verb are agrees with the plural books, not the singular book)

and to enclose sequentially numbered or sequentially lettered items when they are listed horizontally –

      (1) ..., (2) ..., (3) ...
      (a) ..., (b) ..., (c) ...

but no longer when they are listed vertically –

      1. ...
      2. ...
      3. ...

 

Square Brackets [  ]

Square brackets are used to enclose editorial comments and explanations within quotations –

      Jones (1998) continues: ‘It [the palace of Westminster] was destroyed by fire in 1834’

and in some referencing systems to enclose the dates that websites are accessed.