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Parentheses (also called brackets in British English) are a punctuation mark used to contain text that is not part of the main sentence, but that is too important to either leave out entirely or to put in a footnote or an endnote. Since there are many reasons to use parentheses, be sure that the function of parentheses is always made clear to your readers.

Reasons to Use Parentheses

1. To include extra information
The first function of parentheses is to offer extra information. Parentheses communicate to readers that the material inside the parentheses is not necessary to understand the main sentence, nor is it part of the grammar of the main sentence, but is pertinent enough to be included. In the example sentences below, the parenthetical text is not necessary for either the grammatical or the logical completeness of the sentence, but offers some extra, closely related information that the writer felt the reader should have.

This information may be a scientific fact:
"The liquid was brought to 212° F (the boiling point of water) and then poured into molds."

A birth date, death date, or range of dates:
"The anarcho-feminist Emma Goldman (b. 1869) was largely forgotten after her death, but experienced a huge resurgence of notoriety in the 1970s."

A political party affiliation or title:
“Bernie Sanders (I-VT) announced his candidacy for president in Burlington, Vermont, on Tuesday, May 26, 2015.”

Or simply non-essential information:
“My sister (according to Emily, who considers herself almost another parent) has always been the smartest person in the family.”

Simple non-essential information can also be formatted using long dashes, known as em-dashes. Please note that there are no spaces before or after em-dashes:
“My sister—according to Emily, who considers herself almost another parent—has always been the smartest person in the family.”

Parenthetical text can, in addition to being set off with em-dashes or parentheses, be denoted using commas. However, if there are other commas in the sentence, this method of punctuation can become ambiguous, as in the following example:
“My sister, according to Emily, who considers herself almost another parent, has always been the smartest person in the family.”

Here, the use of commas as the sole punctuation mark makes it unclear who “considers herself almost another parent”: “my sister” or Emily.

2. To cite authors
There are many different formats for citing authors and sources within a scholarly text. Many of these formats request that information such as authors’ names and year of publication be given in a parenthetical citation.

When providing citations, be sure that it is clear to your readers what exactly the citation pertains to. For example:

“The proportional carbon content of this component, 20%, is very similar to that found in pine trees (Winston et al. 2010),” implies that the present study has replicated Winston et al.’s prior finding regarding the carbon content of pine trees.

In contrast: “The proportional carbon content of this component, 20%, is very similar to that found in pine trees (See Winston et al. 2010 for a detailed description of the analyses)” clarifies that Winston et al. established the method by which this analysis was carried out, but may not have necessarily had the same findings.

3. To introduce abbreviations
The first time that an abbreviation appears in the main text, it should appear within parentheses next to its full form:

“Interest rates at First Regional Bank (FRB) have risen steadily over the past 20 years, despite FRB’s official corporate policy of offering affordable rates to the community.”

If you offer an abbreviation of a translated term, please specify its original-language form in a parenthetical citation, in italics. This prevents confusion around abbreviations that don’t seem to be logically related to the words they stand for. For example:

“The unexpected closure of the National Development Bank (BND; Banco Nacional de Desarrollo) wreaked havoc on the economy.”

4. To translate words or short phrases
Use parentheses to translate a word or a short phrase into English. For example:

“The Japanese title of Sensei (teacher) conveys the honor and respect accorded to older and wiser members of society.”

Note that Sensei is italicized to clearly denote the non-English word or words being defined.

“Germans wish each other a ‘Guten Rutsch’ (good slide) into the new year.”

Note that, in this second example, the words being defined are a direct, spoken quotation, indicated by quotation marks. Since the quotation marks clearly denote what text is being translated, italics are not needed.

5. To give examples
Use parentheses to offer examples. When using parentheses for this purpose, always preface your list with “e.g.” or other clarifying text.

“While my doctor was glad to hear that I regularly engage in plenty of strength-building physical activities (e.g., yoga, Pilates, and rock climbing), she was concerned that I don’t do anything very aerobic.”

6. To define or restate a word
Use parentheses when you think that readers may benefit from a brief definition or restatement of a word. Such parenthetical text can be a good idea when a word has many possible different definitions, or when you are using a discipline-specific word with an audience who may not be familiar with it. The following example illustrates not only a word that has many alternative meanings, but one that is being used in a way that is likely not familiar to most readers:

“Sports gamblers can spend hours debating the spread (i.e., the number of points between the winner and the loser) of a big upcoming game.”

7. To introduce terms
Use parentheses to introduce terms; i.e., words or phrases that have a clearly defined meaning or scope. Terms presented parenthetically are italicized. For example, in the sentence, “Patients were asked to give examples of bad experiences (trauma) they had experienced as children,” trauma is situationally defined as referring to “bad experiences.” In a paper discussing trauma, a precise and consistent definition of this term ensures that readers do not apply one of the many other logical definitions of the word “trauma.”

Note that “i.e.” can also be used instead of parentheses to denote explanations of terms:

“Patients were asked to give examples of bad experiences, i.e., trauma, they had experienced as children.”

8. To interrupt
The final reason to use parenthetical text is to convey an interruption or an aside. This is common in literature, when reproducing spoken words: “Now, just as the princess was beginning to think that all was lost—yes, Hattie, the princess’s name was Jenny, just like your dolly—she heard a thunderous knock at the front door.”

Interruptions may also be appropriate in very informal scholarly writing: “English is a difficult language to learn (although, according to a number of prominent linguists, it is not even among the top ten hardest, globally), especially for those who have neither a Romance nor a Germanic native tongue.”

However, too many interruptions make it hard for readers to follow your paper’s logic or grammar, and may indicate organizational problems. If you really think that it would be helpful to readers to insert such an unrelated piece of information, a footnote or endnote may be less distracting.

Tips on Parentheses Usage

Whatever the function of your parenthetical text, be sure to place it as close as possible to the word or words that it is supplementing, citing, abbreviating, translating, exemplifying, defining, or restating.

Parenthetical text must stand completely outside of the grammar of the main sentence. To test this, simply remove or insert the parenthetical text. If the sentence’s grammar becomes incorrect or its meaning changes, your parenthetical text is not truly parenthetical.

Sometimes the grammatical and logical separateness of parenthetical text can be deceptive. For example, the sentence “High heels are (particularly) dangerous in wintery weather” really makes two separate statements:

  1. High heels are dangerous in wintery weather.
  2. High heels are always dangerous, but particularly so in wintery weather.

While these two meanings are similar, they are different: the first argues for the dangers of high heels in a specific weather condition, while the second implies that high heels are always dangerous. The writer of this sentence needs to review the point that he or she is arguing: Is the argument that high heels are dangerous in the winter, or that high heels are always dangerous? Failing to correct fuzzy distinctions like these can contribute to muddy logic and hard-to-follow papers.

Using parentheses to compress multiple ideas into a single sentence is also discouraged. For example, a writer might want to compress “We were interested in the advantages of a long-format interview, as well as the disadvantages of a short-format interview” into the more succinct “We were interested in the advantages (disadvantages) of a long (short)-format interview.” Although such a shorthand version may be clear to insiders or appropriate for informal contexts, its logical ambiguity and nonstandard grammar preclude it from use in formal scholarly writing.

Finally, when writing a paper or other scholarly text, parentheses should not be used to indicate sarcasm, or to snidely editorialize. Take the following sentence: “While the Stop and Frisk policy has been (barely) effective in reducing crime, it does so at a great social cost.” Here, the author indirectly grumbles about this policy, but adopts an unprofessional tone and does not fully explain his or her reasoning, reducing the impact of the argument. A more effective tactic is to say exactly what you mean: “The Stop and Frisk policy has been estimated to reduce crime, at most, by less than one percent, and at the social cost of thousands of humiliating and unnecessary public searches.”