Can the second auxiliary be omitted in sentences like "...but she may (have)"?

Question

a. I don’t think she has seen it, but she may (have).
b. This one needs to be repaired; the other already has (been).

Can you omit the second auxiliary? If so, is it more natural to omit it?

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These examples are taken from The Cambridge Grammar (page 100):

Differences between stranding and the central do-support constructions
(a) Stranding not restricted to primary forms
One difference between stranding and the do-support constructions covered in §§2.1.1–3 is that while the auxiliaries in the latter are always primary forms, this is not so with stranding:

[29] i I don’t think she has seen it, but she may have ___. [plain form]
ii This one needs to be repaired; the other already has been ___. [past participle]
iii %He said I was being unfair, but I don’t think I was being ___. [gerund-participle]

This construction is subject to some regional variation: AmE doesn’t allow [iii], but it does have [i–ii], even if they are less usual than versions in which the second auxiliary is omitted.

The book is saying that it's more usual to omit the second auxiliary in [i–ii]. But I for one wouldn't omit the second auxiliary in [i] or [ii], so I have asked the question. Apparently, @EdwinAshworth seems to agree with me, but others seem to disagree. So I think it's worth investigating in ELU.

Answer 1

The answer is different for cases a and b.

In case b, leaving out “been” is acceptable and doesn’t change the meaning. It may seem slightly more fluent to leave it out because it’s a “redundant” word, but it depends on context.

In case a, leaving out “have” potentially changes the meaning. With “have” the sentence is anchored to the present/past and reads as an epistemic statement: “To the best of my knowledge she has not seen it, but I could be wrong”.

Without “have” it reads more like a temporally uncertain statement: “I don’t think she has seen it at this time, but in the future she may see it”.

But the reason for the difference is in which aspects the auxiliary verbs contribute. “May” (or “might”) doesn’t have any past tense aspect(or a past tense sense you could substitute in), so you need to use “have” to contribute that.

Answer 2

(a) is an ordinary example of Conjunction Reduction, and therefore grammatical:

a. I don’t think she has seen it, but she may have seen it
== Conjunction Reduction ==>
a' I don’t think she has seen it, but she may

Conjunction Reduction is a syntactic rule, and is therefore mindless, automatic, and insensitive to meaning, either lexical or contextual.

(b), on the other hand, is ungrammatical:

b. *This one needs to be repaired; the other already has

(b) looks like conjunction reduction (you can put in but or use a semicolon, as you like),
but it doesn't follow the rules required for the rule. In conjunction reduction, the second clause must have the same structure as the first, except for the word that gets deleted because of identity. That doesn't work with this example.

If you try to undo Conjunction reduction with (b), you get

• This one needs to be repaired; the other already has to be repaired.

And this is grammatical, but it doesn't mean the the other has already been repaired. Whoever put the sentence together used been, not be, before repaired, and thus did not replicate the structure required. Never mind what you want it to mean, it's not grammatical with that meaning.

So what to do with the been? Keep it; take off the parentheses. It can't be deleted under identity because it isn't identical.

Answer 3

This construction is subject to some regional variation: AmE doesn’t allow [iii], but it does have [i–ii], even if they are less usual than versions in which the second auxiliary is omitted.

The claim that the second auxiliary is usually omitted is only intended to apply to American English. I'm fairly confident that CGEL is just wrong on this point. I would prefer to include the second auxiliary in both sentences; the versions without them sound awkward, at least with the intended meaning, though I wouldn't call them ungrammatical.

In general, I've noticed that CGEL's treatment of the differences between American and British English is often incomplete or questionable. Both Huddleston and Pullum are Brits; though they've spent a great deal of time in Australia and the US, respectively, neither is a "native" speaker of AmE.

Answer 4

Too long for a comment, so an answer. I confess I find the question and the examples at odds. It looks like the stranding examples are talking about eliding the predicates - ie. not repeating them - and the highlighted words are identifying the stranded forms. I don't see how they could be optional.

In [29]i - I can't use may. Some might choose to not use may - preferring might, but I may not use may and must use might. So "I don’t think she has seen it, but she might have." The have is required.

In [29]ii - has been is required.

In [29]iii - I have never heard the being included locally. It sounds odd, but doesn't seem to hurt anything or shade the meaning one way or another.

American English with a southern bent.