Commas with adverb clauses
Linguistic Reminder
(A similar problem is discussed in French in the reminder Virgule avec un complément de phrase.)
Problem
Since comma rules in English are not always clear-cut, many writers delight in debating them. Rules with adverb clauses can be especially troublesome.
Solution
Use of commas with adverb clauses depends mainly on the position of the clause in the sentence. (However, in the case of a concluding adverb clause—i.e., one at the end of a sentence—the writer needs to determine whether the clause is essential or non-essential.)
Introductory clause
An introductory adverb clause normally takes a comma:
- If you decide to travel by car, the trip will be longer.
Note: It is possible to omit the comma if the clause is quite short and does not require a pause:
- When you call please mention my name.
But even with a short clause, make sure to include a comma if there is a risk of misreading:
- When you call, Janice may be out.
[comma prevents misreading When you call Janice]
Interrupting clause
An interrupting adverb clause—one which noticeably interrupts the flow of the sentence—takes a comma before and after the clause:
- Elephants, when they learn something, never forget it.
Concluding clause
A concluding adverb clause is usually essential to the meaning of the sentence and does not need a comma:
- We arrived as the movie was starting.
Note: Do use a comma before a concluding adverb clause when it gives additional, non-essential information:
- We arrived at 7 o'clock, as the movie was starting.
The phrase at 7 o'clock indicates the time of arrival; the clause as the movie was starting merely gives additional information and therefore needs a comma.
Tip
Use commas with the conjunctions although, even though, though and whereas, which introduce non-essential clauses.
- Sarah valued the gift, although it was not expensive.
Linguistic Recommendation reference number
REM-34/2011-11
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