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Is it correct to use a comma before 'can' in the following sentence? In addition, do I have to use a comma before 'such as'?

Urban pollution largely caused by vehicle emissions, can lead to respiratory problems such as asthma.

Sven Yargs
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Milad
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  • Short answer: none of those commas are needed. – Aleksandr Hovhannisyan Oct 26 '17 at 17:37
  • Whether or not to put a comma before "such as" has been asked and answered on this site before: Is a comma needed before or after “which” and “such as”? – Laurel Oct 26 '17 at 18:13
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    But if you are going to place one after "emissions" you also need a partner for it, after "pollution". They would then form a parenthetical pair, with the rest of the sentence grammatical without the words between commas. – WS2 Oct 26 '17 at 18:25
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    I'd go so far as to say the single comma here is unacceptable. @WS2's suggestion gives the parenthetical, a non-restrictive whiz-deleted relative clause purely adding a relevant bit of knowledge. Omitting both his commas is the other choice, making largely caused by vehicle emissions a restrictive whiz-deleted relative clause (CGEL offers a different classification for these deletions), with the meaning 'That variety / those examples of Urban pollution which is / are largely caused by vehicle emissions ...'/. – Edwin Ashworth Oct 27 '17 at 15:27

2 Answers2

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The sentence should not have any commas. Commas are used to separate phrases which can be removed without altering the structure of the sentence.

You could write the sentence as: Urban pollution, largely caused by vehicle emissions, can lead to respiratory problems such as asthma.

It changes the meaning of the sentence. With the commas, it says that Urban pollution of all types can lead to asthma. Without the commas, it means vehicle emissions cause asthma.

Michael Shulman
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    You start your answer by saying that the sentence should not have any commas and then add a second. Luckily, your correction is correct, even if your assertion is wrong! Specifically, commas are used to separate phrases that can be omitted without changing the overall meaning of the sentence. – Nick Oct 26 '17 at 20:07
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It is possible to read the sentence "Urban pollution largely caused by vehicle emissions can lead to respiratory problems such as asthma" as saying something different from the sentence "Urban pollution, largely caused by vehicle emissions, can lead to respiratory problems such as asthma."

According to this view of the effects of paired commas on sentence meaning, the version without commas limits its focus to "urban pollution largely caused by vehicle emissions," without venturing an opinion about the effects on respiration of other forms of urban pollution.

In contrast, according to the same view, the version with commas asserts that urban pollution (understood as a unitary entity) can lead to respiratory problems such as asthma, and it further asserts that urban pollution is largely caused by vehicle emissions.

In other words, a reader might interpret the commaless form of the sentence as saying this:

Urban pollution of the type that is largely caused by vehicle emissions can lead to respiratory problems such as asthma.

and the two-comma form of the sentence as saying this:

Urban pollution—which, by the way, is largely caused by vehicle emissions—can lead to respiratory problems such as asthma.

So the correct form of punctuation to use depends on which thing you are trying to say.

Sven Yargs
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