Parentheses (( )), also called round brackets, always occur in pairs. They have one major use and one or two minor uses.

Most commonly, a pair of parentheses is used to set off a strong or weak interruption, rather like a pair of dashes or a pair of bracketing commas. In the case of a strong interruption, very often it is possible to use either dashes or parentheses:

The destruction of Guernica — and there is no doubt that the destruction was deliberate — horrified the world.
The destruction of Guernica (and there is no doubt that the destruction was deliberate) horrified the world.

As a rule, however, we prefer parentheses, rather than dashes or bracketing commas, when the interruption is best regarded as a kind of "aside" from the writer to the reader:

On the (rare!) occasion when you use a Latin abbreviation, be sure to punctuate it correctly.
The battle of Jutland (as you may recall from your school days) put an end to Germany's naval threat.
The Basque language is not (as the old legend has it) exceedingly difficult to learn.

We also use parentheses to set off an interruption which merely provides additional information or a brief explanation of an unfamiliar term:

The number of living languages (currently about 6000, by most estimates) is decreasing rapidly.
The bodegas (wine cellars) of the Rioja are an essential stop on any visit to northern Spain.
The royal portraits of Velázquez (or Velásquez) are justly renowned.
The German philosopher Gottlob Frege (1848–1925) laid the foundations of formal logic and of semantics.

In the last two examples, the phrases in parentheses merely provide an alternative spelling of the painter's name and the birth and death dates of the philosopher. In all these examples, neither dashes nor bracketing commas would be possible, except that you might conceivably use dashes in the first. Note also the way I introduce each new punctuation mark in this document.

It is possible to put an entire sentence into parentheses, or even a series of sentences, if they constitute an interruption of an appropriate type:

It appears that 33% of girls aged 16–18 smoke regularly, but that only 28% of boys in this age bracket do so. (These figures are provided by a recent newspaper survey.)

Note that a sentence in parentheses is capitalized and punctuated in the normal fashion.

Do not overdo parentheses to the point of stuffing one entire sentence inside another:

*The first-ever international cricket match (very few cricket fans are aware of this) was played between Canada and the United States in 1844.

This sort of thing is very common in the writing of those who neither plan their sentences ahead nor polish their writing afterward. If you find you have done this, rewrite the sentence in some less overcrowded way:

Very few cricket fans are aware that the first-ever international cricket match was played between Canada and the United States in 1844. or
The first-ever international cricket match was played between Canada and the United States in 1844. Very few cricket fans are aware of this.

Parentheses may also be used to represent options:

The referees who decide whether an abstract should be accepted will not know the name(s) of the author(s).
The (French) horn is an unusually difficult instrument to play.

The point of the last example is that the names French horn and horn denote the same instrument.

Finally, parentheses are used to enclose numerals or letters in an enumeration included in the body of a text:

A book proposal prepared for a potential publisher should include at least (1) a description of the content, (2) an identification of the intended readership, (3) an explanation of why the book will be necessary or valuable and (4) a comparison with any competing books already in print.

Observe that, in contrast to what happens with dashes and bracketing commas, we always write both parentheses:

He was smitten by a coup de foudre (as the French none too romantically put it).

Occasionally you may find yourself placing one set of parentheses inside another. Sometimes this is unavoidable, but you should avoid it whenever possible, since it makes your sentence hard to follow.

Copyright © Larry Trask, 1997

Maintained by the Department of Informatics, University of Sussex