You would think that a few small marks between words every now and then wouldn’t cause so much trouble, but they do, for a lot of people. We looked last time (Some Common Commas) at several standard uses of the comma, including how to use them in a construction called apposition. That use is not only common, but among the commonest of the comma, and so a few more words might be in order.
If I say that my law firm, Smith and Associates, has offices in Chicago and San Francisco, my first intent, the reason I’m putting fingers to a keyboard, is to say something about my law firm; we know that because the standard word order in English places the subject first, followed by its verb. Here, though, we meet with a complication, because no sooner do I declare the subject, law firm, than I decide to name the firm with its proper noun, Smith and Associates. Do I have two subjects, then, or one?
The concept of apposition is meant to sort this out and help us decide on the appropriate punctuation. To appose something (not to be confused with oppose) means to put one thing in proximity to another, and that immediately raises the question of why we’re doing that. Grammatical apposition has two answers: either simply to describe more fully something we’ve already mentioned, or to define more exactly what we’ve mentioned so that the reader does not get confused. From this follows what I think can safely be called an invariable rule of punctuation in modern English: what is merely descriptive is set off with commas; what is defining is not.
In our example, the proper noun Smith and Associates is set aside with a pair of commas, and that is proof positive that I, the writer, thought it might be interesting, useful, helpful—but not necessary—for the reader to know the name of the firm I presumably work for. This kind of apposition is called nonrestrictive, because no obligation is felt to restrict, or hold, the reader’s attention to one particular law firm: I work for only one law firm and here, by the way, is its name. Giving the name of the firm is a way of describing it, and so commas are required, both before and after this nonrestrictive element, in order to signal to the reader that one could cut the entire phrase from the sentence without damaging the grammar and logic—that’s how inessential this merely descriptive element is.
But what about a sentence like this: John Steinbeck’s novel The Grapes of Wrath was published in 1939. The subject now is John Steinbeck’s novel. Just as in the first example, a proper noun, The Grapes of Wrath, is put immediately next to the subject, but this time the phrase is not set off by commas. According to our rule, the absence of commas indicates that the information put in apposition to the subject is now determined to be absolutely necessary in order to define exactly which John Steinbeck novel was the one published in 1939. The writer has therefore not isolated the additional information with commas because that would have worked against the logic: commas separate, and what is essential to something should not be separated from it. If there were commas around the proper noun The Grapes of Wrath, the reader would rightly proceed on the assumption that the phrase could be ignored entirely. But is that true, given the fact that John Steinbeck wrote sixteen novels? Without this element punctuated restrictively, the reader would end up confused.
To restrict, then, means to define what needs to be defined given the reality of the circumstances, and what is necessary is not set off in apposition by commas. When defining is not strictly necessary but describing is felt to be helpful to the reader, the commas around the inessential information do what commas always fundamentally do: separate.