Using Commas for a Parenthesis (Grammar Lesson)

The Quick Answer
Commas can be used to offset a parenthesis (i.e., non-essential additional information in your sentence). For example:
  • While on holiday in London, Simon Schmidt, a fireman from New York, rescued a cat from a tree.
In other words, commas can be used as parenthetical punctuation just like brackets and dashes.
  • While on holiday in London, Simon Schmidt (a fireman from New York) rescued a cat from a tree.
  • While on holiday in London, Simon Schmidt — a fireman from New York — rescued a cat from a tree.

Using Commas for a Parenthesis

Commas can be used to separate a parenthesis (i.e., additional information that is not essential to the meaning of the sentence) from the rest of the sentence. It is also possible to use dashes or parentheses (brackets). When used to offset a parenthesis, commas, dashes, and parentheses (brackets) are called parenthetical punctuation.

Read more about parenthetical punctuation.
Read more about the choice between commas, dashes, and parentheses (brackets).

Examples of Commas Used as Parenthetical Punctuation

In each example below, the parenthesis is shaded:
  • The second boat in the race, the 6-berth Kontarka, was crewed by school children from Pembrokeshire.
  • Mr Tommy Millar, 36, was jailed for robbing his father's grocery store.
  • James, a 23-year-old beggar from Hale, left his 4-million-pound mansion to live on the streets.
  • Last year's GB faggot-eating champion who works with my brother came in here and ate two loaves of bread in one sitting.
    • (This is incorrect because who works with my brother should be separated from the remainder of the sentence using one of the types of parenthetical punctuation, e.g., commas.)
  • Critics search for ages for the wrong word, which, to give them credit, they eventually find.

A Parenthesis Is Not Always Mid-Sentence

A parenthesis is not always mid-sentence. For example:
  • They will be taking Jamie, a young man from London.
    • (When a parenthesis ends a sentence, only one comma (or dash) is needed to offset it. (Obviously, if parentheses (brackets) are used, then both the open bracket and the close bracket are needed.)
When a parenthesis is mid-sentence, you must offset both ends of it; i.e., you cannot use just one comma. For example:
  • Mr Tommy Millar, 36 was jailed for robbing his father's grocery store.

Choose Your Parentheses to Assist Your Reader

Although the use of commas as parenthetical punctuation makes for a normal-looking sentence, commas can become confused with other commas in the sentence. For example:
  • Last night, Josie, an escaped wallaby from London Zoo, attacked two young sisters, Rebecca and Josie, which is pure coincidence, Evans, in a bid to steal their crisps.
    • (Although grammatically correct, the writer could have used a mixture of parenthetical punctuation to make the sentence clearer.)
  • Last night, Josie (an escaped wallaby from London Zoo) attacked two young sisters – Rebecca and Josie (which is pure coincidence) Evans – in a bid to steal their crisps.
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See Also

Using commas (a summary) Our big commas test More about your choice of parenthetical punctuation What is a parenthesis? More about parenthetical punctuation Commas after a sentence introductions Commas after a transitional phrase Commas after interjections (yes, no, indeed) Commas before conjunctions (and, or, but) Commas in lists Commas with a long subject Commas with numbers Commas with quotation (speech) marks Commas with the vocative case Commas with Dear, Hello, and Hi List of easily confused words