This is part of a series about the humble comma, and discusses its role (or lack thereof) in relative clauses.
What Is a Relative Clause?
First, let’s get the gag out of the way. Relative clauses are not parts of a will that define what you’re leaving to your nephews and nieces.
There. Now we can move on.
A relative clause is a clause that provides additional information about a subject without needing to start a new sentence. Additional information is information that, among other things, provides clarity or precision, or helps the reader paint a more detailed mental picture. Let’s take a simple example.
The orange smurf looked decidedly out of place among its blue brethren.
No additional information has been given. Those of us who know and love(?) smurfs get the picture. However, it’s a bare-bones statement; there is no relative clause.
The orange smurf, which had “Made in Ireland” printed on its bottom, looked decidedly out of place among its blue brethren.
The country of origin of the orange smurf is now provided as additional information, perhaps because the author wanted to offer it as a possible explanation for the smurf’s colour (Orange is one of the colours of the Irish flag).
The orange smurf that had “Made in Ireland” printed on its bottom looked decidedly out of place among its blue brethren.
Here the author is providing information that helps identify a specific orange smurf.
“Which had ‘Made in Ireland’ printed on its bottom” and “that had ‘Made in Ireland’ printed on its bottom” are both relative clauses. Neither sentence would be any less grammatically correct if the clause was removed, but the first would lose information and the second would lose precision. In the world of relative clauses, the first is “non-restrictive” and the second is “restrictive”. But it’s not the “which” and the “that” that make the difference—it’s the commas.
Restrictive/Defining/Identifying Relative Clauses
The purpose of a restrictive relative clause is to define or identify which of a number of possible subjects the sentence refers to—it restricts the scope of the sentence.
“That had ‘Made in Ireland’ printed on its bottom” is a restrictive relative clause. It identifies a specific orange smurf—the one with “Made in Ireland” printed on its bottom. Without that defining information, we might be left wondering which orange smurf it was that looked out of place.
Restrictive relative clauses are introduced with “that” (or who or whom or whose).
The Chicago Manual of Style maintains that the word “that” may be omitted if the sentence is just as clear without it, such as the following.
The car that I rented was less comfortable than my own car.
The car I rented was less comfortable than my own car.
Non-Restrictive/Non-Defining/Non-Identifying Relative Clauses
The purpose of a non-restrictive relative clause is to provide additional, non-essential information about the subject—its omission would not reduce the precision of the information.
“Which had ‘Made in Ireland’ printed on its bottom” is a non-restrictive relative clause. The information about the smurf’s country of origin hasn’t been provided to identify/define which specific smurf we’re referring to—it’s been provided as “by-the-way” information.
Non-restrictive relative clauses are also known as non-defining relative clauses and non-identifying relative clauses.
Where Does the Comma Come into All This?
Now we understand the difference between restrictive and non-restrictive relative clauses, answering that question is a piece of cake.
Non-restrictive relative clauses are always delimited by commas.
Restrictive relative clauses are never delimited by commas. In the case of the optional “that”, whether you include or omit the word “that”, you still do not delimit with commas.
British English—Breaking its Own Rules One at a Time
I grew up in England, and I learned that I could use the word “which” to introduce a restrictive relative clause (although I have to say that I was never explicitly taught about restrictive and non-restrictive relative clauses!) So in the UK (and possibly in other parts of the world), the following sentences are both valid, even if they mean something different.
The orange smurf, which had “Made in Ireland” printed on its bottom, looked decidedly out of place among its blue brethren.
The orange smurf which had “Made in Ireland” printed on its bottom looked decidedly out of place among its blue brethren.
There are two lessons to be learned here.
- If you’re writing a particular variety of English (I write in both British and Canadian English), you need to be careful which word you use.
- The commas are all the more important in British English, because they are all that distinguish a restrictive relative clause from a non-restrictive relative clause.
What Happens When You Use the Wrong Kind of Clause?
Let’s reconsider “The orange smurf that had “Made in Ireland” printed on its bottom looked decidedly out of place among its blue brethren.”
The construction of the sentence implies that the reason the orange smurf looks out of place is because it has “Made in Ireland” printed on its bottom and not because it’s orange. The reader is led to infer that there are other orange smurfs in the picture that were made elsewhere than Ireland. That’s likely not what the author had in mind; such are the perils of using a restrictive relative clause where a non-restrictive one was needed.
This may sound trivial while we’re using smurfs in our examples, but what if we were addressing a safety topic? And especially if we were writing in British English?
The orange wire, which is nearest to the timer, should be cut first. Failure to do so will result in immediate ignition of the bomb.
The orange wire that/which is nearest to the timer should be cut first. Failure to do so will result in immediate ignition of the bomb.
Do they sound the same to you? What if there are two orange wires in the bomb—do they sound the same now? In the first example (the non-restrictive one), the bomb disposal person would be on the radio to someone asking which orange wire to cut. In the second example, he or she would know which one to cut—the one nearest to the timer.
The Long and Short of it
The delimiting commas make all the difference to the information contained between them and to the information’s relationship to the rest of the sentence. In non-British English, the use of “that” or “which” helps clarify which kind of relative clause is being used; in British English, it’s usually only the presence of the commas (and perhaps the context) that tells you.
Bottom line—be sure to use the commas where they are needed, but only where they are needed.
Especially if you’re writing about how to defuse a bomb.
Please Help Improve Yonder Pedant’s Ramblings
- Did I miss a typo? (I’ll feel bad when you tell me, but I’d rather you did tell me!)
- Did I write something that makes you want to turn green and burst out of your shirt?
- Do you have any better examples that you would share and allow me to use?
If so, please let me know by leaving a comment.