Commas for parenthesis
 
Commas can be used to offset additional information in your sentence (called parenthesis). For example:

While on holiday in London, Simon Schmidt, a fireman from New York, rescued a cat from a tree.

(also covered in the lesson Parenthesis)
 

Commas for Parenthesis

Commas can be used to separate additional information (called parenthesis) from the rest of the sentence. It is also possible to use dashes or brackets. When used in this way, commas, dashes and brackets are called parentheses. (See lesson Parenthesis.)

Examples (with each example of parenthesis 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.
  • ("who works with my brother" should be separated from the remainder of the sentence using commas)
  • Critics search for ages for the wrong word, which, to give them credit, they eventually
    find.

Not Always Mid-Sentence

A parenthesis is not always mid-sentence. For example:

  • They will be taking Jamie, a young man from London.

Choose Your Parentheses to Assist Your Reader

Although the use of commas for parentheses makes for a normal-looking sentence, they can become confused with other commas in the sentence.

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 parentheses in order 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.
See also: A choice of parentheses
 
PARENTHESIS? 

A parenthesis is additional information in a sentence. If a parenthesis is removed, the sentence still makes sense.
 
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. 
("who is my sister's friend" is additional information. This is a parenthesis.)

Comments such as however, therefore, as a result, as far as I am concerned, etc. 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)
 

See also:

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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