Only when my mental capabilities returned, like a slow-motion boomerang, did I absorb the implication of the situation.

Do I need the "did" in the sentence above? Why or why not?

Long ago, someone told me I needed to write "did" in these situations. However, I checked on Google books and some don't include it:

Only when my mother would bother herself enough to bring me some tea or draw me a bath would they start to go away.


2 Answers 2


This question is about sentences that begin with adverbials with a negative meaning. In these sentences, the subject and the auxiliary verb are inverted. You can find other examples with only here: only if, only after, only then, etc and not until. For details of other negative adverbials, for example under no circumstances, see the Oxford Guide to English Grammar, page 27.

You can only play after lunch.
Only after lunch can you play

This same inversion is much more common for questions and negatives, so these are much better understood and documented. Here is an example:

He can play the piano.
Can he play the piano?

But what happens if you need to invert and there is no auxiliary verb? The answer is that you insert do as an auxiliary verb, and then swap it.

He ... plays the piano.
He does play the piano.
Does he play the piano?

In your first sentence, there is no auxiliary verb so it is necessary to add did before the subject I. In the second sentence, would is the auxiliary verb, so there is no need to add do: you just move would before the subject (they).


It is required, because it is the action verb in this sentence. An action verb is required because the format is generally "Only when (something happens) [can I] [verb/do something]."

In your second quote, I'm assuming it's sole purpose is to disprove the statement that "did" is required.

However, "would they" is equal to "did I."

In these situations, you should remember that "did I" is interchangeably equal to "was I able to."

If you reread your sentence and it makes sense when you replace "did I" with "was I able to," then you are using it correctly.

  • Oh, it never occurred to me to use "would they." Is "would they" more commonly used in cases like these?
    – alex
    Jan 21, 2018 at 9:08
  • @JavaLatte I was attempting to explain my answer in a manner that even a non-native English speaker could comprehend with.
    – Bellator
    Jan 21, 2018 at 9:21
  • @alex No, "would they" and "do I" are not always going to be interchangeable. I simply meant that they both serve the same purpose, but they will not always express the same verb tense.
    – Bellator
    Jan 21, 2018 at 9:22
  • 1
    @JavaLatte I clearly said, "in these situations," they are equal. Meaning, only in this situation and similar uses of the phrase are they equal. However, I do get your point about my answer not being entirely correct and missing key information. I'll take your advice and do more research on topics before I answer.
    – Bellator
    Jan 21, 2018 at 9:37

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