As we have seen in this blog, commas cause more anguish for writers – beginning, student, and even professional ones – than any other punctuation mark. In fact, in the lists of twenty common errors in undergraduate writing, mistakes with comma use account for a quarter of the items. While professional writers do not usually have comma splices, they do have about the same number of comma errors as students do.
Included in the misuses of commas are some like comma splices and other unnecessary comma uses. While a whole post is focused on commas that are not needed, this post focuses on principal misuses.
As we saw in the earlier blogs on quotation marks and punctuation, a comma precedes a direct quotation: Mary said, “I am ready.” While a comma sets off a direct quotation, a principal misuse of the comma is to set off an indirect quotation, when you are reporting what someone has said without using the exact words; for example:
Experts say, that pollution is damaging. [wrong]
Experts say that pollution is damaging. [correct – no comma]
Another misuse of the comma is to set off a single word that isn’t a nonrestrictive appositive. In an earlier post on comma use with appositives, we saw that commas are used to set off nonrestrictive appositives because they are considered extra information so they are unnecessary to the meaning of the sentence. But restrictive appositives, as well as other restrictive elements, are essential to a sentence’s meaning so no commas are used. It’s easy when the appositive is one word to think that it should be set off with commas, but as the following sentence illustrates, a single word appositive that is restrictive uses no commas.
Experts say that the pollutant, ozone, is especially damaging. [wrong – misuse of commas]
Experts say that the pollutant ozone is especially damaging. [correct – no commas: The word ozone is essential to the meaning because there are many pollutants, but it is ozone that is especially damaging.]
As we saw in the post on unnecessary commas, another principal misuse of commas is to separate sentence constituents that go together. Commas should not be used to separate 1. subjects and verbs, 2. verbs and objects, 3. verbs and subject complements, or 4. prepositions and objects.
- subject and verb: The laptop on the table, is mine.
- verb and object: The dog understood at once, what his handler wanted.
- verb and subject complement: The only thing the lottery winners wanted was, to live their lives as they had before becoming millionaires.
- preposition and object: On her way home from work, she bought a book at, the bookstore.
There is no magical formula for accurate comma use. Most uses are conventional and follow established usage rules, though some uses require judgement calls. Writers develop the necessary judgment only through lots of reading and writing. Through that reading and writing, they also learn times and ways to bend or break the rules for rhetorical effects.