The comma between city and state—or, following the same principle, between city and province or city and country—is so thoroughly inscribed in the written record that most editors don’t give it a second thought.
But what, exactly, is that comma doing? And is it always necessary, no matter the context?
An Organizing Comma
The comma separating the name of a city from the name of a state or other region is, first and foremost, an organizing comma. It allows readers to distinguish the two entities as belonging to different categories:
Chicago, Illinois
London, Ontario
London, England
That’s one of the roles played by this comma, but there’s a second principle at work.
An Abbreviated Relative Clause
When a comma sets off a state or province or country from a city, it introduces an abbreviated relative clause. Here’s how that works:
I live in Chicago, Illinois.
is equivalent to
I live in Chicago, in Illinois.
or, stated more fully,
I live in Chicago, which is in Illinois.
The relative clause as spelled out in that last example—“which is in Illinois”—is nonrestrictive, or parenthetical. A parenthetical relative clause is set off with a comma (or two in the middle of a sentence) and introduced by the relative pronoun “which” (or a form of “who,” as when referring to a person rather than a city; see CMOS 6.27 [17th ed.]).
The clause is parenthetical because the information it provides is optional; specifically, you don’t need it to identify the noun to which it refers. And if I say I live in Chicago, you should know where that is. The name of the state (Illinois) may help some readers, but it isn’t essential.*
Parenthetical or Essential?
Chicago, however, is unique (or very nearly so). For many other cities, the name of the state might be restrictive, or essential.
For example, if I said I visited Portland, would you know what I’m talking about?
If you knew somehow that my visit coincided with the coast of New England in the United States, then you’d probably know what I meant. Without sufficient context, however, the identity of Portland would be in doubt. I could be referring to Portland Maine or Portland Oregon, among other Portlands.
As an editor following Chicago or practically any other style, however, I would be obliged to go back and add three commas—of the organizing kind—to that last sentence (see CMOS 6.39 and 10.29 [17th ed.]):
I could be referring to Portland, Maine, or Portland, Oregon, among other Portlands.
Those commas—all three of them (or four, if you count the one after “Oregon,” which, if it weren’t busy setting off the prepositional phrase at the end of the sentence, might still be required)—are not only cumbersome (they risk appearing at first to set up a series rather than a pair of alternatives), but they break the rule that says not to use commas with essential relative clauses.
Here’s how that works in this case:
I could be referring to Portland Maine or Portland Oregon, among other Portlands.
is equivalent to
I could be referring to the Portland in Maine or the Portland in Oregon, among other Portlands.
or, stated more fully,
I could be referring to the Portland that is in Maine or the Portland that is in Oregon, among other Portlands.
Essential relative clauses, including the two in that last example, typically begin with “that” (though “which” is common in British English, and a form of “who” may be used when the reference is to a person), and they’re not set off with commas.
Unlike parenthetical relative clauses, an essential relative clause can’t be deleted without obscuring the identity of the noun to which it refers. Try it: “I could be referring to Portland or Portland, among other Portlands.” Without the state names, that sentence doesn’t make any sense.
Possessive Avoidance
There are lots of potential Portlands, from London, Ontario, and London, England, to Duluth, Minnesota, and Duluth, Georgia. If a city has a name, chances are good it’s not the only city with that name.
So what’s wrong with leaving out the comma? Not only is there no ambiguity in a reference to Miami Florida or Paris Texas, but omitting the comma would spare us from some awkward constructions, chief among them the possessive: Miami Florida’s skyline is a lot easier to like than Miami, Florida’s, skyline—or, if you prefer, Miami, Florida’s skyline.
If it were up to me, the comma would be optional for just that reason. But it’s not, so I follow Chicago’s advice to rewrite as needed to avoid the possessive (e.g., “the Miami, Florida, skyline” or “the skyline of Miami, Florida”; see also CMOS 6.43 and 6.44 [17th ed.]).
Another Loophole, or Maybe Two
There is, however, a third principle at work here. A city and state are like the first and last names of a person. A surname isn’t a state, but it does name a family, and a person could be said to belong to a family just as a city belongs to a state. So why not Bob Dylan from Duluth Minnesota?
And one more: If the comma’s organizing role is so important, then certainly it could be dropped when referring to Duluth, MN, or London, ON, or London, UK. Those two-letter abbreviations in all caps clearly belong to a different category from the spelled-out cities, without any help from the commas.
Back to Reality
It would be wrong to leave out the well-established “City, State” comma in formally edited prose. Readers have come to expect that comma, so its absence would be more of a distraction than its presence. Not that I wouldn’t be prepared to make an exception for two cities with the same name mentioned in an either-or scenario (as in the Portland/Portland example). But that’s a special case.
When the state or province or country is abbreviated, on the other hand, commas can seem like overkill. You’d think they could simply be omitted, as Chicago and others decided to do decades ago with Jr. and Sr. in people’s names, a roughly parallel scenario. But don’t worry, that’s not about to happen—not unless you count the style long preferred by the US Postal Service for addresses on mailing labels.
* There may be one or two other Chicagos out there, but the context of this post narrows it down to just the one.
Top image by Flavijus Piliponis / Adobe Stock.
Editor’s Corner posts at Shop Talk reflect the opinions of its authors and not necessarily those of The Chicago Manual of Style or the University of Chicago Press.
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Russell Harper (@cpyeditor) is editor of The Chicago Manual of Style Online Q&A and was the principal reviser of the last two editions of The Chicago Manual of Style. He also contributed to the revisions of the last two editions of Kate L. Turabian’s A Manual for Writers of Research Papers, Theses, and Dissertations.
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