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I'm writing a scientific paper and my coauthor claims that ending a sentence with "did" is ungrammatical. The sentence has the following form:

Half the boys jumped, but only a quarter of the girls did.

Is he correct?

How can we describe the grammatical role that did is playing here, by standing in for the already-mentioned verb "jumped"? Is it a pro-verb (not to be confused with a proverb)? Where can I find rules for where pro-verbs can and cannot appear in sentences?

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    This is Conjunction Reduction with optional Do-Support. Yes, it is called a "pro-verb" (pronounced differently, of course), and do is one of the most common pro-verbs. It is completely grammatical; your colleague is incorrect. Require them to cite a rule next time they try to correct your grammar. – John Lawler Jan 27 '15 at 19:10
  • It's a perfectly fine sentence. Several ways one might reword it, but I doubt that any would be noticeably better. – Hot Licks Jan 27 '15 at 19:34
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The sentence is fine grammatically, and the pattern is very common in English in both informal and formal speech and writing.

Did is an auxiliary verb, but what is more interesting is what is NOT there: the verb jump is understood to be there grammatically, just like you is understood to be the subject in Stop criticizing my grammar!

This is an example of verb phrase ellipsis.

From Wikipedia:

Verb phrase ellipsis

Verb phrase ellipsis (also VP-ellipsis or VPE) is a particularly frequent form of ellipsis in English. VP-ellipsis elides a non-finite VP. The ellipsis must be introduced by an auxiliary verb or by the particle to.

John can play the guitar; Mary can [play the guitar], too. - VP-ellipsis
He has done it before, which means he will [do it] again. - VP-ellipsis

An aspect of VP-ellipsis that is unlike gapping and stripping is that it can occur forwards or backwards. That is, the ellipsis can precede or follow its antecedent, e.g.

The man who wanted to [order the salmon] did order the salmon. - VP-ellipsis
The man who wanted to order the salmon did [order the salmon]. - VP-ellipsis

  • The quote from the Wikipedia article is missing what looks like the all-important crossing out of what can be omitted. Your quote didn't make sense until I looked at the article. And just as I posted this you edited it. Ignore this, sorry. – Jonathan Spirit Jan 27 '15 at 19:31
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    Yes, I saw that at the same time you did [see it]. Thanks. :) – Jim Reynolds Jan 27 '15 at 19:34

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