Why should you use a comma before which in this sentence:
- The fire, which occurred in 1666, destroyed a large part of central London
Is an example without a comma incorrect?
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Sign up to join this communityWhy should you use a comma before which in this sentence:
Is an example without a comma incorrect?
I shall try to be succinct, for a fuller explanation, see this answer by StoneyB, as suggested by user178049.
Both with and without commas, your sentence would be grammatically correct, but they would mean slightly different things.
With commas, the clause inside the commas becomes a nonrestrictive relative clause. This means that it is there to add extra, non-essential information to the sentence. The meaning of the sentence doesn't change if you were to remove the clause entirely.
Without commas, the clause becomes a restrictive relative clause. This means that it provides essential information, restricting the noun it modifies to uniquely identify it. Removing the clause would change the meaning of the sentence. (Some people will tell you that you can't use "which" and must use "that" for a restrictive relative clause, but this is not a strict grammar rule used universally.)
So, if you wish to identify which fire by saying "which occurred in 1666", then don't use commas. If you want to add extra information about a fire that has already been identified, then use commas.
What you are looking at is a dependent relative clause.
If the "which occurred in 1666" part is a nonrestrictive phrase (also an adjective clause) then it requires a comma:
A nonrestrictive phrase adds a little bit of extra (but not essential) information about a noun phrase that you’ve already mentioned in your sentence.
which introduces a nonrestrictive phrase. Therefore, you need a comma before which and another one at the end of the nonrestrictive phrase.
If the same part is a restrictive phrase then it should appear without commas and be an essencial part of the sentence.
https://www.grammarly.com/blog/comma-before-which http://www.cws.illinois.edu/workshop/writers/clauses