What is correct in a sentence: "Only then can you do" or "only then you can do" ?

  • "Only you can prevent wildfires" - Smokey Bear – Elliott Frisch Jan 31 '14 at 13:51
  • Only then can you do is the common construction, as you are taking the words out of their common SVO and putting them in a somewhat set-by-tradition manner in this example. – anongoodnurse Jan 31 '14 at 15:31

After only then in this context, inversion is pretty much obligatory.

  • A Google Ngram adds support to the truth of this observation, with which I also agree. Barrie stresses that context is important: you can, of course, wangle acceptable counter-examples. You might prefer completing the Peekaboo Loop from Bryce Point to tackling the Navajo Loop from Sunset Point, only then you can do the Queens Garden Trail too. – Edwin Ashworth Jan 31 '14 at 14:15

The phenomon that the normal order of sentence elements is changed is called inversion, subject-verb inversion. Inversion is found regulary if the first position of the sentence is occupied by an adverb with negative or restricting character. Such adverbs/adverb groups are: hardly, scarcely, never, no sooner, under no circumstances, in vain and similar expressions. In spoken language the regular order of sentence elements is perferred. "only then" is an adverb group with restricting character so in written style you will find inversion. But this does not mean the normal sentence order is impossible. And of course there are other types of inversion.


In your first example, you have given an example of V2 (verb-second) order. This was the default syntax of Anglo-Saxon. The verb was almost always the second element in the sentence. Let us take a closer look at your example:

'Only then can you do.'

I have italicized the adverbs. As you can see, they form a sort of adverbial unit. After them is the verb in the second position. Then we have the subject you and then another verb; in Anglo-Saxon, the subject often succeeded the verb. I will give another example below:

'Over tips the boat.'

'The boat tips over.'

As you can see, both of these sentences sound natural, while 'over the boat tips' does not. Although we are seeing more frequent use of simple SVO (subject-verb-object) order where V2 was historically preferred, V2 is still prevalent in many constructions. Your example is one of these.

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