For today’s Tuesday grammar tip, I wanted to share an obscure grammar rule you’ll find buried in the pages of the 16th edition of the Chicago Manual of Style. (You can read more on why someone would want to use CMOS in this article.) This rule is something I learned once I started working as an editor, and it’s one not very many people are aware of but one many people use incorrectly.
I call it the “not/but” rule, and the best way to illustrate this is with a few examples. See if you can’t spot the changes:
1) I’m not only tired but also feeling sick.
2) I’m not only tired, but I’m also feeling sick.
Do you see anything different? In example #1 there’s no comma, but in #2 there is a comma. Why?
When “but” is not followed by a subject, there should be no comma before it. In other words, if what comes after “but” is not an independent clause, then the use of a comma before it is incorrect. In the case of #2, there is a subject (I’m) that comes after “but,” therefore a comma is necessary.
Here’s another example:
-He’s not only great at playing the piano but also the trumpet.
-She’s not only great at playing the piano, but she’s also great at the trumpet.
Hopefully this helps you understand the basic rule. What I see most often are unnecessary commas added before “but.” Ex: He’s not only great at playing the piano, but also the trumpet. The comma in this case is incorrect and should be removed.