My question arises from this one, where OP asks whether he should use the singular or plural verb form after "the title, as well as the tone,"
As luck would have it, when I searched Google Books for exactly that text, I found…
The title as well as the tone of this volume errs, perhaps, in being unduly modest.
…and…
The title, as well as the tone, of the novel derive from Lady Molly Jeavon's household
At the risk of having this question closed as just peeving, I feel that the first one should have been plural "err", because without the commas it seems to me both "the title" and "the tone" have more or less equal status as "joint" subjects of the verb, making it plural.
On the other hand, I feel the commas in the second example effectively demote "the tone" to "parenthetical" status (the clause is almost incidental). Since this encourages us think of "the title" as the primary subject, it should have been singular "derives".
I'm no great fan of "grammatical rules", but it seems weird to me that the only two relevant examples for this specific wording should both (in opposite ways!) contradict my inclinations.
What's going on?
Best Answer
The question seems to me to turn on whether or not as well as is a coordinator. If it is, then the following verb behaves as if and had been used instead, that is, the subject becomes plural and so does the verb. But as well as says something that and does not. And places the two items on an equal footing, but as well as gives grammatical priority to the first item. How would it be if the sentence were The title in addition to the tone of this volume err(s), perhaps, in being unduly modest? That means much the same, but if you have reservations about making the verb singular after as well as, you may well have far fewer reservations about making it singular after in addition to.