Sentences that start with an “only” adverbial, usually referring a particular time or condition, have a curious structure as they typically require an auxiliary verb and an inversion. These sentences can come in many tenses, and are usually emphatic. Here’s few examples:
- Only after the sun went down, did the bats come out.
- Only if you finish your homework can you go to the park.
- Only when we had eaten the pie did we realise that it was out of date.
So how do we use this structure?
Only after / when / if inversions
Two clauses connected by an “only after / when / if etc.” adverbial can be reversed like other sentences with multiple clauses and a conjunction – simply requiring the extra inversion of the main verb and subject.
- They cleaned up the river only when it started turning green.
- Only when it started turning green did they clean up the river.
- They cleaned up the river when it turned green.
- When it turned green, they cleaned up the river.
Note that the “only after” adverbial clause does not use a comma, unlike other reversed adverbial clauses.
“Only after / when / if” adverbials can also be used to start sentences that contain only when it is used as an adverb alongside the main verb, too, if you can find the rest of the adverbial later in the sentence (such as after, when, if). The time or condition adverbial needs to be combined with “only” and moved to the front of the sentence. If this is the case, be careful to group all the words together with the adverbial, as the time or condition may be made up of multiple words. How would you reverse these sentences?
- We only found the treasure then.
- You can only read the comic after the football game has finished.
- I only want your help if you’re willing to work quietly.
- He only danced when others weren’t looking.
Remember that the “only after / when etc.” adverbial comes first, then we invert the auxiliary verb (or add an auxiliary verb and invert it), then place the rest of the sentence in the same order as before.
- Only then did we find the treasure. (note that found becomes the bare infinitive find, because have added an auxiliary verb)
- Only after the football game has finished can you read the comic.
- Only if you’re willing to work quietly do I want your help.
- Only when other weren’t looking did he dance.
We add auxiliaries for statements in the simple tenses. We add to do for actions and to be for states. If you have a perfect, continuous or modal tense you won’t have to add an auxiliary verb. When starting a sentence with one of these only adverbials, you always need to put the auxiliary verb before the subject, though.
- They could drive home only after it stopped raining.
- Only after it stopped raining could they drive home.
The purpose of this construction is simple, even if the grammar is a little lofty. We use it to emphasise the condition, or the restriction. This is a strong way to show resistance to doing an action or event, or to emphasise a restriction. The auxiliary verb helps achieve this, in the same way that we might add an auxiliary for other emphatic statements: “I did do my homework – honestly!” “Only after / when etc.” adverbials bring particular attention to the conditions – giving us a negative aspect, rather than a simple sequence of events – to go back to some of our examples:
- Only after the river turned green did they clean it. (implying they waited too long)
- Only if you’re willing to work quietly do I want your help. (implying you have a problem with making too much noise)
Hopefully this helps clear up this construction – if you have any questions, as always, let me know.