...a useful symbol the existence of which many novices, and many professional writers as well, particularly journalists, seem to have irretrievably forgotten.
Plain Style, p. 56
The Chicago Manual of Style devotes one page to the period, one page to the semicolon, two pages to the colon, and wholly eleven pages to the comma. Even the otherwise mysterious question mark gets little more than a page, and its louder cousin, the exclamation point, doesn't get even one.
This week, Research as a Second Language will be devoted to the comma, which "indicates the smallests break in sentence structure" (CMS 6.18). In standard Danish prose, use of the comma follows a hard and fast grammatical rule (which, like many Danes, I will one day learn as well). In English, however, "Effective use of the comma involves good judgment" (ibid.).
Let's start with how the comma can be used to set off appositives. "An appositive noun is one that immediately follows another noun or noun phrase in order to define or further identify it" (CMS 5.29). It's a good place to start because it involves the important distinction between restrictive and non-restrictive parts of sentences. The latter are "omittable", as the CMS (6.43) puts it, while the former are "esssential".
Stewart Clegg's first book, Power, Rule, and Domination, was published in 1975.
Here's an example of the non-restrictive appositive noun phrase. To see that it is non-restrictive, you need merely to notice that the phrase "Stewart Clegg's first book" and the title "Power, Rule, and Domination" refer to the same thing. The latter does not restrict the meaning of the former, i.e., it does not make the sentence refer more precisely to something in the world.
Stewart Clegg's first book was published in 1975.
Power, Rule, and Domination was published in 1975.
These two sentences are just as true as the first, though they are, of course, less informative. But consider the following sentence.
Stewart Clegg's book, Power, Rule, and Domination, was published in 1975. (Wrong)
I have simply removed the adjective "first" before the noun "book". The sentence as it stands now is, in fact, misleading. It suggests that Clegg has written only one book. I could have replaced "first" with "only" to emphasize this (but it would, of course, only have made it directly false).
Here we can see what the commas are doing. The right way to write this sentence is:
Stewart Clegg's book Power, Rule, and Domination was published in 1975.
The word "book" is actually unnecessary here. But the point is that the title is essential to the meaning of the sentence; it restricts the meaning of the phrase "Stewart's Clegg's book", which could otherwise refer to other books.
Stewart Clegg's book was published in 1975.
This sentence would only really work in a paragraph that had already distinguished Clegg's contribution from someone else's.
Well, that's all I have time for this morning. Tomorrow, while jogging, I will try to come up with a pithy rule of thumb for setting commas. That's actually a pretty daunting task. See you then.