Which form of punctuation is best suited for non restrictive clauses within a sentence?

by Craig Shrives

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A non-restrictive clause is a clause that provides additional, non-essential information. In other words, a non-restrictive clause is not needed to identify the word it modifies, i.e., it's just bonus information. As a non-restrictive clause is not essential to the meaning of a sentence, it is offset with commas (or some other parenthetical punctuation such as dashes).

Here is another example of a non-restrictive clause.

Peter Jones , who plays goalkeeper for our village football team, has worked at his father's greengrocers for twenty years.

identify

Non-restrictive clauses contrast with restrictive clauses. Look at this example of a restrictive clause:

The man who plays goalkeeper for our village football team has worked at his father's greengrocers for twenty years.

identifies

You are not limited to commas when offsetting a non-restrictive clause. You can use parentheses (brackets) or dashes too. (See Reason 2 below.) Read more about your choices of punctuation for offsetting a non-restrictive clause.
Here are some more examples of non-restrictive clauses:

I went to London with John Baker, who lives next door.
Betty, who is still on the ferry, will arrive before 4 o'clock.

Read more about using commas with "which," "that," and "who." Here are some more examples of non-restrictive clauses in real-life quotations (non-restrictive clauses shaded):

Every journalist has a novel in him, which is an excellent place for it. (Historian Russell Lynes)
Humans are the only animals that have children on purpose with the exception of guppies, who like to eat theirs. (Journalist P J O'Rourke)
She had a pretty gift for quotation, which is a serviceable substitute for wit. (Playwright W. Somerset Maugham)
You can talk about anything if you go about it the right way, which is never malicious. (comedian Rodney Carrington)

When looking at writing errors, there are more issues associated with restrictive clauses than non-restrictive clauses. As a general observation, non-restrictive clauses do not cause too many snags. Nevertheless, here are two good reasons to give non-restrictive clauses a little more thought. Writers often ask whether to put a comma before "who" and "which." The answer to that question is sometimes yes and sometimes no. It depends whether the "who" or "which" heads a restrictive clause or a non-restrictive clause.

Look at this example:

My brother, who lives in New York, caught coronavirus.
My brother who lives in New York caught coronavirus.

Remember that if your adjective clause is essential to identify its noun, then there are no commas. If it's just additional information, use commas, dashes, or parentheses (brackets)...or delete it.

Test for a Non-restrictive Clause

If you'd happily put it in parentheses (brackets) or delete it, use commas. The example above uses "who." Here's one with "which." There is a distinction between "who" and "which" because Brits are okay with a restrictive clause headed by "which," but, as a rule, Americans aren't.

I've enjoyed the benefits of this country, which has been very good to me. (Attorney Wendy Long)
How can you govern a country which has 246 varieties of cheese? (French President Charles De Gaulle)

Read more about using "who," "which," and "that" (go to Issue 1 on this link). Commas are the most common type of parenthetical punctuation, but, for certain effects, you can use others. Here are some guidelines:

Choice of Parenthetical Punctuation	Pros and Cons
commas	(pro) normal-looking sentence (con) commas are often confused with other commas in the sentence
brackets	(pro) parenthesis easily seen (con) brackets make official letters look a little unorganized
dashes	(pro) parenthesis easily seen (con) dashes look a little stark

Read more about your choices of punctuation for offsetting a non-restrictive clause.

Do you have an adjective clause headed by "which" or "who"? Would you happily put it in parentheses? Yes? It's non-restrictive. Offset it with commas or, if you think it helps, dashes or parentheses (round brackets).
Knowing your options for parenthetical punctuation is a useful writing tool.