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I am a volunteer English tutor. My advanced ESL student wrote the following sentence after reading an article:

However, recent studies, in Sweden and in Finland, have found out that different patients suffering from diabetes could be divided into 5 groups, depending on which cluster they suffer from.

Of the four commas in the sentence, I marked commas 2, 3, and 4 as unnecessary. He argued that he was taught that because "in Sweden and in Finland" and "depending on which cluster they suffer from" are non-essential, they need commas around them.

I am more or less certain that the commas around "in Sweden and in Finland" are wrong and pretty sure that the last comma is also unnecessary, but I do not know how to explain how these are essential when non-essential elements, "elements embedded in the sentence that interrupt it without changing the essential meaning" according to Purdue, can be a bit subjective when talking about elements that add more information. Both elements can be removed from the sentence without changing its core (another 'how to determine if it's essential' tip I read), but the commas simply do not look right.

Am I in the wrong? Are these points of information that give the reader more detail non-essential and should actually be surrounded by commas? If not, how do I explain to the student how to determine when additional information is essential or non-essential?

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    "However, recent studies in Sweden and in Finland have found out that different patients suffering from diabetes could be divided into 5 groups, depending on which cluster they suffer from". The final comma is optional, though best omitted. – BillJ Mar 6 '18 at 20:24
  • I am not convinced that a focus on essential/non-essential information is the best way to decide on the need for commas. As @AndyT says, commas represent the pauses you would make if speaking the sentence. So I would suggest that you practise reading complex sentences aloud with your student and seeing if you can agree on where the natural pauses occur. In your sentence, they would, for me, be after however and groups. – Shoe Mar 7 '18 at 11:25
  • Commas two and three aren't wrong when the writer's intent is to supply that information non-restrictively, i.e., as non-essential information, instead of restrictively, i.e., as essential information. Since the writer made it clear to you that he intended that information as non-essential, meaning conveying what country the studies took place in wasn't germane to his point, then the commas are right. The fourth comma is also not wrong. In fact, not including it is wrong. It precedes an absolute phrase that modifies the entire preceding clause, not just the preceding noun "groups." – Billy Jul 6 '18 at 4:04
  • The point of punctuation in grammar is to help convey meaning in written communication. The writer explained what his meaning was, and what that meaning was jibes with how we use commas when that is the intended meaning. Just because you might have written it differently or just because you find that information to be essential rather than non-essential has no bearing. All that matters is what the writer meant, and the grammar the writer used was exactly right for what he meant. – Billy Jul 6 '18 at 4:10
  • Maybe you'd have found it more palatable if the writer had instead written "...recent studies, which were in Sweden and in Finland, have found..." However, English does not require a writer categorically precede all non-restrictive modifiers with "which." How this writer did it is perfectly grammatical. – Billy Jul 6 '18 at 4:32
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Comma 2 is unnecessary because it splits the subject clause into two parts. The specification "in Sweden and in Finland" distinguishes the research from other recent ones (for example, compare it with "the girl with the blue skirt") and as such it qualifies as necessary.

Comma 3 is definitely wrong because it splits subject and verb.

Regarding Comma 4, I would insert it, as it gives some breath to an otherwise long sentence. However, I think this is matter of personal preference rather than grammatical correctness.


I think that your student interpreted "in Sweden and in Finland" as a parenthetical element. From the link:

A parenthetical element is a word or group of words that interrupts the flow of a sentence and adds additional (but nonessential) information to that sentence.

Normally, parenthetical elements are isolated from the rest of the sentence with commas, as your student did with "in Sweden and in Finland".

Jane, the girl with the blue skirt, likes to drink green tea.

If we replace "in Sweden and Finland" with its parenthetical equivalent ("recent studies, which were conducted in Sweden and in Finland, have found out...") then comma 2 and 3 become not only correct, but also necessary; however, were we to excise the parenthetical element, the sentence would become "recent studies have found out...".

  • About comma 3: non-defining relative clauses have commas even if the comma separates subject and verb. See writingcenter.unc.edu/relative-clauses ("My mother, who is an excellent cook, is thinking of opening a restaurant."), ef.com/english-resources/english-grammar/… ("John's mother, who lives in Scotland, has 6 grandchildren."), learnenglish.britishcouncil.org/en/quick-grammar/… ("The skirt, which is a lovely dark blue colour, only cost £10.") – hvd Apr 6 '18 at 13:07
  • @hvd your examples are all parenthetical elements, which I mention in the second part of my answer; as far as I can tell, non-defining relative clauses are a subgroup of parenthetical elements. I should clarify my answer with regard to your comment. – LinuxBlanket Apr 6 '18 at 13:17
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    @hvd parenthetical elements need two commas around them. If we replace "in Sweden and Finland" with its parenthetical equivalent ("recent studies, which were conducted in Sweden and in Finland, have found out...") then I agree on both comma 2 and 3; however, were I to excise the parenthetical element, the sentence would become "recent studies have found out...". I regard the two commas before and after the non-defining relative clauses as signalling the beginning and end of such elements, thus being effectively part of them. – LinuxBlanket Apr 6 '18 at 13:31
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    I still don't understand why "in Sweden and Finland" cannot be a parenthetical element by itself the way the student took it. This isn't explained by your answer or your link. You assert "its parenthetical equivalent" is "which were conducted in Sweden and in Finland". It's possible you're right about that, but given that that is such a major point of the question, can you explain in your answer why? – hvd Apr 6 '18 at 13:48
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    @hvd "in Sweden and Finland" can be a parenthetical element, and "which were conducted in Sweden and Finland" can be a non-parenthetical element (defining clause?). It's a matter of the speaker's intent; both variants are grammatical. – Lawrence Jun 5 '18 at 22:35
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This is why "non-essential" and "essential" are misleading terms, and should be replaced by "non-restrictive" and "restrictive".

The clause "in Sweden and in Finland" is a restrictive clause because it addresses the question "which recent studies?" (unless you believe that there was only one set of recent studies) and thus there should be no comma. The fact that you can remove the clause from the sentence without making it nonsensical does not change the fact that this is a restrictive clause.

Finally, I believe the sentence reads much better with the fourth comma than without it.

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The student's logic in including commas 2 and 3 is fine, but it doesn't scan right to me.

I find it easiest to think of commas as "pausing in speaking". I can certainly see a situation where someone speaking might realise at the last second that they should mention "in Sweden and in Finland" and therefore pause before saying it, but it wouldn't be expected when reading the sentence.

I would say that "in Sweden and in Finland" is describing the "recent studies", and therefore should tied closely to it. Your student may as well say that "recent" is non-essential information, and put a comma between that and "studies" - it's just as valid and just as unlikely.

If he wanted to separate out the "in Sweden and in Finland" he should make it more of a separate clause, by making it "such as in Sweden and in Finland" or "which were carried out in Sweden and in Finland".


The final comma is a matter of opinion. Personally I would pause in speaking there, and so would write a comma. Others dislike commas there.

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    I agree about retaining the final comma. Without it the sentence may be momentarily parsed as groups depending on the cluster ... = groups that depend on the cluster ... , whereas in fact it is the division that depends on the clusters. – Shoe Mar 7 '18 at 11:14

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