When a verb such as "can" is modified by "only", the meaning of the sentence becomes rather negative (impossibility rather than possibility), and to me it sounds strange to use the negative tag "can't it?". On Google Books I find an example of an author doing it so,

It can only be Jagged Sky we're aiming for, can't it? (The Empty Sea, by Craig Michael Curtis)

But I'm not sure it's the most cautious literature. I would have said "isn't it", based on meaning:

It can only be Jagged Sky we're aiming for, isn't it? (= isn't it Jagged Sky we're aiming for?)

Is there a rule, and what is the actual usage?

EDIT: I understand that since "be" was present in the first example, my alternative suggestion is confusing as it seems to be related to it. A second example is:

Lorries can only use the main road, can't they?

where I wonder whether one would employ this negative tag or rather a positive one, "can they?" (="can they use other roads?")

  • 2
    The default "rule" is if the preceding assertion being presented for confirmation includes an auxiliary verb (can, in your examples), the "inverted / negated" form of that verb is used in the tag question. Hence It can be fixed, can't it?, It can't be fixed, can it? Including only makes no difference to that rule, so it's I can only try, can't I? Feb 20, 2020 at 13:17
  • @FF Are you sure that's the default rule in 'AmE'? Feb 20, 2020 at 13:19
  • ... See, for instance, We have plenty of time, don't we? / , haven't we?. Feb 20, 2020 at 13:23
  • @EdwinAshworth: I've never bothered to "study" such matters. I just made up that rule on the fly. I initially started with a comment saying the tag verb was always the verb from the preceding "assertion", but I edited to include reference to auxiliaries before clicking "Add Comment". The only specific AmE/BrE difference I know is Younger Brits often don't bother choosing between possible tag question verbs, innit? Feb 20, 2020 at 13:28
  • 1
    Syntactic rules are not made up from meanings; they're automatic, like digestion, and are triggered by individual words and constructions. Meanings get supported and enhanced, but nothing like directly. It's an evolutionary process, as Darwin pointed out. Feb 20, 2020 at 15:16

3 Answers 3


Lorries can only use the main road, can't they?

is grammatical, idiomatic, and is asking for confirmation of a fairly strong conviction. ('I think this is true; I'm correct, aren't I?'

Lorries can only use the main road, can they?

is equally grammatical, and uses a tag question either showing a degree of surprise at this newly disclosed piece of information, or sarcasm at a claim known to be false.

Sorry, no references on this one.


The tag question negates only the active verb. Negating an already negated active verb results in a positive.

In the sentence, can is the active verb and "be" is an infinitive, i.e. not active, and thus "be" is not repeated. Thus, "can" becomes "can't/cannot" in the tag.


It can only be Jagged Sky we're aiming for, can't it?

It is only Jagged Sky we're aiming for, isn't it?

See https://www.englishclub.com/grammar/tag-questions.htm

  • In the question mentioned in a comment above, the acceptability of not echoing the 'active verb' in a tag question is addressed. / Again, there are no authoritative references. Feb 20, 2020 at 13:25
  • @Edwin Ashworth: My apologies, I thought a non-contentious and/or elementary explanation would not require such a reference.
    – Greybeard
    Feb 20, 2020 at 14:30
  • 'Non-contentious and/or elementary' neatly sidesteps the issue that what you overtly assert (the tag verb always echoes the verb in the matrix sentence) is contentious, as the answers at the duplicate prove. Site policy is for answers to be accompanied by authoritative references (or, if 'elementary', not to be answered but either close-voted as inappropriate, or close-voted as better asked on ELL). The only exception is where the answerer is known to be a renowned published academic, like Professor Lawler (who usually gives links in any case). Feb 20, 2020 at 15:52
  • Well your own link is barely in agreement with your answer, is it? It provides examples such as "She can rarely come these days, can she?"
    – Joce
    Feb 21, 2020 at 12:39

Based on the link provided by @greybeard, https://www.englishclub.com/grammar/tag-questions.htm, two elements:

  1. The verb in the tag has to be the active verb indeed, "can" and not not "be" in the OP original sentence.

  2. It will not always be negated, if there is already a negative meaning implied. The link provides examples:

Negative adverbs

The adverbs never, rarely, seldom, hardly, barely and scarcely have a negative sense. Even though they may be in a positive statement, the feeling of the statement is negative. We treat statements with these words like negative statements, so the question tag is normally positive. Look at these examples:

He never came again, did he?

She can rarely come these days, can she?

You hardly ever came late, did you?

I barely know you, do I?

You would scarcely expect her to know that, would you?

However, "only" is not in the list.

  • I covered your point 2. in "Negating an already negated active verb results in a positive." - perhsaps I could have been clearer.
    – Greybeard
    Feb 21, 2020 at 13:17
  • @Greybeard One question is whether "can only" is already negative or not.
    – Joce
    Feb 21, 2020 at 14:21

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