Why can you omit "is" at the end of "no matter how foul their mood"?

Question

In a recent episode of Frieren, one character said:

But people have to work to make a living no matter how foul their mood.

On one hand, it seems like this sentence is missing the word "is" at the end, but on the other hand, the sentence makes sense to me, and I don't feel that it is incorrect.

It seems to me that some sort of verb phrase ellipsis is involved, but wikipedia says that VPE requires that "its antecedent can be found within the same linguistic context", which does not seem to match the situation here. Perhaps it is a different kind of ellipsis?

Grammatically, what is going on?

Answer 1

Short answer (tl;dr)

This is a verbless Predicate-Subject construction (yes, Predicate first and Subject last). It is allowed here because it is functioning as the subordinate clause in an exhaustive conditional. It's not really a case of the be being deleted. It's more a case of there being no tensed verbs occurring in this particular type of verbless construction to begin with.

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The Full Story

1. People have to work to make a living no matter how foul their mood is.
2. People have to work to make a living however foul their mood is

You can, in principle, omit the copula, BE, in both of the bolded clauses above. The basic precondition for this is that both of these sentences are a special type of conditional known as an exhaustive conditional construction.

A normal, run-of-the-mill conditional tells us that under some certain condition described in the subordinate clause, the main clause will be true:

3. If it rains, I'm staying home.

The subordinate clause in an exhaustive conditional takes the form of a subordinate interrogative clause depicting a particular question/issue. The sentence as a whole tells us that it does not matter what the answer to that question is, or the resolution of that issue is. The main clause will be true in any case.

4. However lightly it rains, I'm staying at home.
5. Whether it rains or not, I'm staying at home.

We are interested here in conditionals like (4), where the subordinate clause is introduced by an open interrogative word. (We will note in passing that the subordinate clause can appear on either side of the main clause).

"Deleting" BE in exhaustive conditional protases

You will see in (1) and (2), that when the subordinate clause in the conditional begins with an open interrogative word, this word must have the suffix ‑ever. However, we can also get conditionals where the subordinate clause appears as the complement of another word or idiom. In the case of (1), the idiom is no matter. In such cases the suffix ‑ever is no longer necessary because that job is being done by the idiom itself.

I described these being subordinate clauses in conditionals [the technical term is protases] as a pre-condition for their being able to be "reduced". However there are a number of other criteria that must also apply:

6. *People must work, however foul their mood may. (ungrammatical, needs be)
7. *People must work, however foul their mood seems to. (ungrammatical, needs be)
8. *People must work, however unjust they know that it. (ungrammatical, needs is)

The examples above are all ungrammatical because the verb be must be the first verb in the verb phrase, and must be tensed— as was the case in (1) and (2). [Another way of putting the same thing is that there can be no other tensed verb heading the construction].

The following are ungrammatical too:

9. *People must work, no matter how unfair it.
10. *I will always take work, no matter what a job.
11. *They won't employ anyone at all this round, no matter how good John.

As shown above, the Subject of the "missing" be, cannot be a personal pronoun, an indefinite noun phrase or a proper noun.

The following versions are all fine:

12. People must work, no matter how unfair the arrangement.
13. I will always take work, no matter what the job.
14. They won't employ anyone at all this round, no matter how good the candidate.

Ellipsis, reduced clause, or a different construction?

The Original Poster has already realised that this cannot be a case of so-called verb phrase ellipsis (VPE). She notes that VPE requires that its antecedent can be found within the same linguistic context, and that doesn't seem to be the case in (1, 2). Another, more basic, reason to eschew such an analysis is that VPE requires a preceding auxiliary verb. And as we have seen there is no verb preceding the missing BE in any of these cases.

Another view we might take is that these are tensed, finite interrogative clauses where the interrogative word or phrase has been fronted (as is normal in interrogative clauses) and where the verb be has been deleted.

However, Arnold and Borsley (2014), following Cullicover (2013), make a good case that these exhaustive protases which look as though they have been "reduced" by removal of the word be are actually special Predicate-Subject constructions. English allows verbless Subject-Predicate constructions, for example the with clause in:

15. They came out with their hands tied behind their backs.

In (15), the bolded string means their hands were tied behind their backs. However, as it is the complement of the preposition with, no finite verb is allowed in that string. Some scholars refer to such strings as verbless clauses.

So Arnold & Borsley's argument is that the type of protasis seen in the Original Posters example is actually not a reduced finite clause but a Predicate-Subject construction in its own right, where, crucially, the Predicate must come first and the Subject of that Predicate must come second.

This, they convincingly argue, explains one last condition that other accounts cannot. Which is that the interrogative word or phrase, which occurs first, cannot be a Subject. It can only be a Predicate. For this reason the following example is ungrammatical:

16. *We will have a celebration, no matter which students successful.

In (16) the interrogative phrase which students appears first, as is required by this interrogative. However, it is the Subject of the clause and cannot appear in this construction before the Predicate phrase successful, and is thus ungrammatical. It is fine if we use a regular finite interrogative instead:

17. We will have a celebration, no matter which students are successful.

[Note that if Arnold & Borsley are correct, the interrogative phrase has not "moved" to the front of the construction. There is no perceived "gap" or deletion at the end there. In their terms this is not a "filler" construction]

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Executive summary

In the Original Poster's example no matter how foul their mood can occur without the verb be at the end for a number of reasons.

Firstly, it is a special verbless Predicate-Subject construction licensed because it is occurring as a protasis in an exhaustive conditional.

Secondly, it does not break any constraints that apply to the construction:

• the Subject of the construction, their mood follows the interrogative Predicate phrase how foul.
• the Subject of the construction, their mood, is a definite noun phrase and is not a pronoun, proper noun, or indefinite noun phrase.
• there is no tensed verb heading the construction.

That's all folks!

References

Arnold, D. and R.D. Borsley (2014) On the Analysis of English Exhaustive Conditionals. In: Proceedings of the 21st International Conference on Head-Driven Phrase Structure Grammar, University at Buffalo. CSLI Publications, 27 - 47.

Culicover, Peter W. (2013), Grammar & Complexity: Language at the Intersection of Competence and Performance. Oxford: Oxford University Press.