If two wh-clauses appear as the subject of a sentence, is the verb singular or plural?
Two or more wh-words might occur side by side and function as (part of) subject. Such subjects may be finite or nonfinite clauses: are they plural or singular in number?
To take when-and-where subjects for example:
When and where it first became the conventional system that a weary or inattentive infant in a class must have its face smoothed downward with a hot hand, or when and where the conventional volunteer boy first beheld such system in operation, and became inflamed with a sacred zeal to administer it, matters not.
It is yet a long and weary path, and when and where to strike it is now our greatest difficulty.
It read like a love affair, an assignation, though when and where were a blank.
Chuncan Feng firstname.lastname@example.org www.eduscitech.com China Posted 22 February 2003
Usually, but not always, two wh-clauses would have a singular verb.
We need to apply both a semantic rule and a grammatical rule to the sentences.
Sentence 1 is stylistically complicated, but can be paraphrased as
When and where [the idea] that a weary or inattentive infant in a class must have its face smoothed downward with a hot hand first became the conventional system.
When and where the conventional volunteer boy first beheld such system in operation, and became inflamed with a sacred zeal to administer it, doesn’t matter.
Now that we understand its structure, let’s look at the original version of Sentence 1, correctly punctuated:
When and where it first became the conventional system that a weary or inattentive infant in a class must have its face smoothed downward with a hot hand, or when and where the conventional volunteer boy first beheld such system in operation and became inflamed with a sacred zeal to administer it, matters not.
Each of the two clauses introduced by when and where can be considered as a single unit of thought, and therefore the verb should be the singular, is. There’s a further reason for using the singular verb. The grammatical rule decrees that with two subjects separated by or, the verb should be singular—except when at least one of the subjects is a plural noun. This is not the case here. Therefore the verb should be singular: first, because each occurrence of when and where is seen as a single unit of thought, and second, because the two wh- noun clauses are separated by or, which requires a singular verb.
Sentences 2 and 3 do not have a grammatical rule as much as a semantic one. The choice depends on whether the speaker or writer considers the two pairs to be a single unit, or as separate entities.
In sentence 2, the writer conceives of the ideas of when and where to strike as a single issue and therefore uses the singular verb is.
Sentence 3 contains an ellipsis—an omission of material that might follow when and where. Each of these ideas (e.g., when the (imagined) love affair/ assignation might have taken place plus where it might have taken place) is considered important in its own right and is treated as a separate idea. This view of the ideas as separate prompts the plural verb were.
This is not the only possible view. The two ideas—when and where—could just as easily be considered a single unit, and the verb could have been was. The choice of verb number depends on the writer’s view of the ideas.
I’ve found a couple of similar usages in Google with how and whether:
How and whether to use such a consultation to discuss drinking is trickier.
How and whether to model other agents is a ubiquitous issue in MAS.
In general, then, nominal clauses with pairs of wh-words as grammatical subject take a singular verb, unless the two ideas are viewed as separate.