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
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
it, doesn’t matter.
Now that we understand its structure, let’s look
at the original version of Sentence 1, correctly punctuated:
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
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
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
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
the plural verb were.
This is not the only possible view. The two ideas?b>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
viewed as separate.