The Editors’ Association of Canada email list has lately had a discussion on the topic of sentences such as “Victoria, BC is a pretty place” – or should that be “Victoria, BC, is a pretty place”?
It’s quite common not to use the second comma. And in fact in most cases one is not too likely to misunderstand the sentence without it. But does it belong there, strictly speaking? And if so, why?
My answer is yes, technically, it does belong there. The “BC” is an appositive. Compare:
I visited John, the butcher, and he made meat pies.
I visited John, your nephew, and and we drank too much.
I visited Cochrane, Alberta, and saw my parents.
I visited Cochrane, Ontario, and saw not much worth reporting on.
Why have that second comma for appositives? Clarity and syntactic coherence. Here are a couple of contrasting examples:
When I visited John, the butcher, and he made meat pies, we all drank too much. [John is the butcher; he made meat pies.]
When I visited John, the butcher and he made meat pies, and we all drank too much. [John is not the butcher; he made meat pies with the butcher.]
One could argue that it would be better just to go with postal abbreviations as post-modifiers:
I visited Cochrane AB and saw my parents.
I visited Cochrane ON and saw not much worth reporting on.
It would be difficult to do that with full words, though:
I visited Cochrane Alberta and saw my parents.
But if you’re going to put one comma in, you need to put a second in; otherwise you’re signalling the beginning of a new phrase:
Although I like Cochrane, Alberta is kind of dry.
Consider a parallel case where both options would be coherent but different in meaning:
I saw David, the accountant in our office. [David is the accountant in our office; I don't say where I saw him]
I saw David, the accountant, in our office. [I saw David in our office; I don't say where he's an accountant normally]
So, by the same logic, we use commas on both sides of the province name.