Partial series
I've been seeing grammatical constructions like this a lot lately (examples made up by me), both in fiction and elsewhere:
- He had lived in California, Oregon, and had been born in Nebraska.
- She voted for Clinton, Gore, and was a staunch Democrat.
- I like cheese, pickles, and I'm awfully fond of onions.
(There's a slight structural difference between that third one and the first two, but it's irrelevant to my point, and I've seen both structures recently.)
The problem here is that each of these sentences is structured as if it presents a three-part series, but the third part isn't grammatically parallel to the first two, so it's not actually a three-part set; it's a two-part set with a third grammatically unrelated clause tacked on.
The easiest way to resolve this is generally to change that first comma to an "and" (and sometimes to also remove the second comma):
- He had lived in California and Oregon, and had been born in Nebraska.
- She voted for Clinton and Gore, and was a staunch Democrat.
- I like cheese and pickles, and I'm awfully fond of onions.
Sometimes you can instead change the third clause to match the first two: "I like cheese, pickles, and onions."
