Using Commas for a Parenthesis (Grammar Lesson)
 
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 parentheses (i.e. 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.
 

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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 hildren 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 the 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, they 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.
 
WHAT IS A PARENTHESIS?

A parenthesis is additional information in a sentence. If a parenthesis is removed, the sentence still makes sense. For example:

  • The defendant, Mr Michael Evans, sat in silence.
  • (Mr Michael Evans is additional information. This is a parenthesis.)

  • The last owner of the Red Lion, who is my sister's friend, won over 4 million on The National Lottery.
  • (The clause who is my sister's friend is additional information. This is a parenthesis.)
Comments such as however, therefore, as a result, and as far as I am concerned fall into the category of parenthesis too.

  • John Winfield, on the other hand, is an experienced jockey.

  • We have really everything in common with America nowadays except, of course, language. (Oscar Wilde)
Read more about the definition of parenthesis.
 

See also:

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




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