This post is the third in a series of posts on comma use. The first post dealt with commas and coordinating conjunctions. The second dealt with non-standard commas and punctuating for length. Today’s entry will discuss the way that some commas work best in pairs. Compare these three sentences:
This innovative new technique, developed by Woljert, has altered the way this surgery is performed.
This innovative new technique, developed by Woljert has altered the way this surgery is performed.
This innovative new technique developed by Woljert, has altered the way this surgery is performed.
The first sentence clearly conveys its meaning to the reader: there is an innovative new technique that has altered the way some surgery is performed. The reader is also given supplementary information: this technique was developed by some researcher named Woljert. This element (‘developed by Woljert’) either takes two commas (as in the first sentence) or takes no commas (‘This innovative new technique developed by Woljert has altered the way this surgery is performed.’). A single comma here (as in both the second and third sentences) will throw off your readers because it doesn’t clarify the grammatical role of the adjacent information.
When clauses like this appear at the beginning or end of a sentence, the need for paired commas is obviated:
According to Chen, this new technique is very valuable.
This new technique is very valuable, according to Chen.
This new technique, according to Chen, is very valuable.
In each of the first two sentences, an additional comma becomes unnecessary because of the placement of the clause at the beginning or end of the sentence. In the third sentence, we see the need for two commas to clarify the role of this brief interruption. (Of course, you will have noticed that the first sentence sounds much better than the other two. You don’t generally want to give this sort of unimportant information such a prominent place at the end of the sentence. Similarly, you don’t generally want to interrupt a sentence in this fashion unless the interruption itself is significant.)
This use of one comma instead of two (or none) isn’t a particularly grammatically complex issue, but it is a frequent occurrence in the student writing I see. And while it isn’t fatal, it does make your reader’s life more difficult. In lots of cases, this mistake may just be random carelessness; it’s certainly easy to miss a comma here or there. But if you repeatedly use a single comma when two (or none) are needed, you may be experiencing some confusion between restrictive and nonrestrictive clauses: not knowing whether to use no commas (as you would for a restrictive clause) or two commas (as you would for a nonrestrictive clause), maybe you split the difference and use just one. Come back for the next comma post, in which I will try to sort out the difference between restrictive and nonrestrictive clauses. As I will stress then, this distinction is most crucially an issue of punctuation, but I will also touch on the persistent dilemma experienced by writers trying to choose between ‘which’ and ‘that’.