Subscribe to The Chicago Manual of Style Online
Q. It’s my observation that increasingly, in a sentence like this, the commas are being omitted, no matter how many sisters there are: “I wanted to go to the store, but my sister Sara refused.” Can’t we just admit that it’s cleaner and easier to omit them most of the time, unless there’s genuinely a clarity issue? The world is changing; can we make this official? Thank you.
A. In casual correspondence and the like, it’s OK to omit such commas wherever details related to family composition are unimportant or irrelevant (in other words, most of the time). So “my sister Sara” is totally fine in casual usage even if Sara is your only sister (and therefore functioning as a nonrestrictive appositive, which would normally be set off by commas). Consider that official. In more formal prose, however, these commas can be important. In a work of history or a biography—where the presence or absence of commas will help readers follow the narrative—they are essential. In other types of works, the rule can often be relaxed. (That’s not an official ruling, but it is a practical one.) For more on restrictive versus nonrestrictive appositives, see CMOS 6.28.