This is from "The Lion King":

Nala: And your mother, what will she think?

Simba: She doesn't have to know. Nobody has to know.

Nala: Of course they do!

Why doesn't she reply: "Of course they have!" ?


To omit the rest of the sentence, you need an auxiliary verb. And sometimes, have is an auxiliary verb:

Have you taken out the trash?
Yes, I have [taken out the trash].

Here, have is an auxiliary verb, so the rest of the sentence can be omitted as long as it can be understood from context.

If you don't have an auxiliary verb, you can insert the meaningless auxiliary do:

You like eggs, right?
Yes, I do [like eggs].

Note that you can't simply say "Yes, I like", because like isn't an auxiliary verb. You need an auxiliary to omit the rest of the sentence.

And in your example, have is not an auxiliary. In this sense, it's a lexical verb:

She doesn't have to know. Nobody has to know.
Of course they have to know!

Since it's not an auxiliary verb, the rest of the sentence can't be omitted. But if we insert the meaningless auxiliary do:

Of course they do [have to know]!

Then we can omit it.

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  • Actually, I think have is not a lexical verb but a fossil spelling of the first syllable of the recently evolved 'enhanced' modal hafta. Note that with the "have to" and "got to" phrasals a)the "verb" and "to" cannot be separated: modifiers cannot be placed before "to" b) the phrase can stand by itself for the full VP: "Nobody hasta know? Of course they hafta!" But the evolution is so recent that the default pro-verb do is also in play. – StoneyB on hiatus Feb 28 '14 at 14:02
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    Further examples: "Nobody wants to know", "Of course they want!" is incorrect. "Nobody has ever known", "Of course they have!" is correct. "Nobody wants anything", "Of course they want!" could be correct, but only if the second speaker isn't eliding words as snailplane is talking about, rather they've switched to using "want" as an intransitive verb, which changes the meaning a little. – Steve Jessop Feb 28 '14 at 14:38
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    Oh, and "Nobody must know", "Of course they must!" is correct, again because "must" is an auxiliary verb. And I think "Nobody has to know", "Of course they have to!" is correct, although I wonder whether some "don't split infinitives" fanatics would object to treating "has to" in that way. I think they shouldn't because as StoneyB says "have to" is a modal. – Steve Jessop Feb 28 '14 at 15:00
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    @StoneyB Hafta fails the main tests for a modal auxiliary: it doesn't negate, it doesn't invert, and it doesn't appear in tag questions. See The Morpholexical Nature of English to-Contraction for a more detailed rejection of the idea that hafta is either a lexeme or a modal, and specifically page 100 for discussion of the evidence from VP ellipsis. – snailplane Feb 28 '14 at 19:25
  • @snailplane I will read this when I have the leisure to do so properly; but you're quite right; I should have called it a 'quasi-' or 'semi-'modal. But it belongs to a group (it's a little early to call it a 'class') that appears to be in the process of replacing the traditional modals at the same fairly rapid pace with which they were introduced. – StoneyB on hiatus Feb 28 '14 at 19:50

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