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I can't seem to determine whether or not the second half of the sentence below is restrictive or non-restrictive and thus, whether or not a comma is needed? While it doesn't seem necessary, it does seem to be rather important.

However, a previous history of drug use was found to be strong predictor of program success, which suggests that interventions should be put in place sooner rather than later.

I've spent the last little bit going over restrictive and non-restrictive clauses, as well as dependent and independent clauses separated by coordinating conjunctions and am a tad confused at this point. Is this a case where it is a case of personal preference?

Any help is appreciated.

Many thanks!

Richard Kayser
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Alex K
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  • You can replace << , which >> with << , which fact >>, << ; this >> (or even << . This >> ) here, showing that the whole part of the sentence following success is non-specifying (non-restrictive), ie tacked-on comment/s. The comma is necessary. – Edwin Ashworth Apr 30 '20 at 15:41
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    Does this answer your question? "Which" or "what" or ... when referring to a main clause? (Shoe's answer): 'Bob writes on the blackboard which causes a screeching noise.' vs 'Bob writes on the blackboard, which causes a screeching noise.' The comma shows that ['Bob writes on the blackboard'] (ie the entire main clause) 'is the cause of the screech'. – Edwin Ashworth Apr 30 '20 at 15:45
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    @EdwinAshworth. Thanks for the link. I've added an answer below with information from what may be considered a more authoritative source. – Shoe Apr 30 '20 at 16:07
  • No, not personal preference. There can only be one "previous history of drug use was found to be strong predictor of program success", so the relative clause is non-restrictive, and should be set apart with a comma. – BillJ Apr 30 '20 at 16:24
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    It's up to you to decide if something you write is meant to be restrictive or nonrestrictive. If you rephrased this sentence to use that and no comma (as well some other tweaks to make that acceptable), then the meaning becomes restrictive. It's a kind of chicken-and-egg scenario. But since the use of which with a comma clearly indicates it being nonrestrictive here, and there is no other evidence that it's a mistake, that's almost certainly the correct meaning and punctuation. – Jason Bassford Apr 30 '20 at 17:56
  • Thank you everyone for their input. BillJ (above) seems to suggest that this is not at all a matter of choice. Is this correct? – Alex K May 01 '20 at 07:46

2 Answers2

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There are other ways to classify relative clauses than restrictive and non-restrictive. The Cambridge Grammar of the English Language (p1034), for example, lists integrated, supplementary, cleft, and fused relative constructions.

Your sentence has an example of what the CGEL would call a supplementary relative clause. It states:

The supplementary relative...permits a much wider range of antecedents, as is evident from examples such as:

  • i. Pat is afraid of snakes, which I'm sure Kim is too.
  • ii. Pat is afraid of snakes, which doesn't surprise me at all.

The antecedents for which here are an AdjP in [i] and a whole clause in [ii]... .

Your sentence is an example of the [ii] type. The "which suggests that interventions should be put in place sooner than later" relative clause has the whole "a previous history of drug use was found to be strong predictor of program success" main clause as its antecedent.

Supplementary clauses must be marked off with a comma. The CGEL says:

The information expressed in this type of relative is presented as supplementary, and this is reflected in the fact that the relative clause is characteristically marked off prosodically or by punctuation from the rest.

Shoe
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  • Yes; CGEL is far better than Swan here. A specimen answer; perhaps the question I linked to should be closed. Or should this perhaps have been added there? – Edwin Ashworth Apr 30 '20 at 16:56
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You have asked a good question. But at first I want to clarify the defining (restrictive) relative clause and non-defining (continuative) relative clause with two examples :

Now compare the following two sentences :

(A) The place where I went to school is a wonderful town. (B) Edinburgh, where I went to university, is a beautiful city.

In (A) We can’t say “The place is a wonderful town” … why? Because we don’t know which place it is. This means that it is essential to put the complete defining clause :The place "where I went to school" is a wonderful town. (Here the quoted part is a Defining Relative Clause because it defines or describes its antecedent "The place". This clause clearly defined which place it was. Therefore, we DO NOT USE COMMAS here.

In B it is possible to say “Edinburgh is a beautiful city” and “where I went to university” is an extra information that grammatically is not necessary. Both parts are grammatically complete sentences (grammatically this type of Relative Clause is called a non-defining Relative Clause, because it does NOT define the subject, it only adds information, this type is written with COMMAS at the beginning and end).

Therefore, your posted sentence contains a non-defining relative clause : However, a previous history of drug use ....... predictor of program success, which ( = and it ) suggests that interventions should be put in place sooner than later.

Here the relative clause is adding extra information about the program success, and here which stands for 'and' it'. It's therefore a non-defining relative clause and a comma should be used before 'which'.

Hope, it's now as clear as daylight! Thank you, everyone.

Sandip Kumar Mandal
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  • Thanks for your reply. However, is the clause (after which) not essential to the meaning of the sentence? Without it, would a reader not be led to believe that a past history of drug use predicts program success in of itself? However, the point of the sentence is that this information is important because it suggests interventions should be used sooner than later... Thanks! – Alex K May 01 '20 at 07:50