Consider the following:

Not only does she keep cats but she also keeps dogs.

I wonder why "does" is before the subject. Is it a rule, governing parallelism? And also, is the regular form acceptable too? I mean:

Not only she does this but she also does that.

Also, is there any other rule governing parallelism?

  • 1
    Please consider "Not only does she keep cats but she also keeps dogs" which uses a different verb. Commented Oct 13, 2020 at 16:36
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    If you start the sentence with not only, you have to use the inversion. That is a rule.
    – Lambie
    Commented Oct 13, 2020 at 17:28

2 Answers 2


The inversion occurs due to the fronted negative adverbial - not due to the parallelism. Fronted negative adverbials in non-parallel sentences show the same inversion:

Never have I heard of such a silly thing.

You can also say "I have never heard of such a silly thing" - but you can't say "Never I have heard of such a thing", which would be ungrammatical.

Cambridge gives these examples:

Never have we witnessed such cruel behaviour by one child to another.

Seldom does one hear a politician say ‘sorry’.

Not for a moment did I think I would be offered the job, so I was amazed when I got it.

It is equally possible to write "We have never witnessed..." or "One seldom hears..."or "I didn't think for a moment...". But you can't write "Never we have witnessed".

Similarly, "not only" doesn't need to be fronted. But if it is fronted, inversion must be used.

Parallelism itself doesn't require inversion. Your example is inverted because of the fronted negative:

Not only does she do this but she also does that.

("She not only does this but she also does that" works, too. But what you called the "regular" form, "Not only she does this", would be ungrammatical.)

But if it was "sometimes", there would be no inversion:

Sometimes she does this but other times she does that.

Or "On Wednesdays":

On Wednesdays she goes to the gym but on Thursdays she doesn't.

Again, no inversion is possible. "On Wednesdays does she go" would be ungrammatical in modern English - other than as a question.


Rule governing starting a sentence with not only:

To add emphasis, we can use not only at the beginning of a clause. When we do this, we invert the subject and the verb: Cambridge Dictionary

And add the auxiliary if there isn't one.

  • She keeps cats and dogs. Not only does she keep cats and dogs, she also has a bird.

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