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I understand some of the sentences with frequency or degree adverbs (hardly, seldom, scarcely etc.) are regarded as negative sentences, though they "look" like affirmatives, in that they would come along with their affirmative tag questions, or they would receive "So auxilary-verb subject."

"You hardly ate the lunch, did you? (Not *didn't you?)"
"You hardly ate the lunch. Are you okay?" "Neither did you. (Not *So did you) Are you okay?"

Now, does this apply to "barely" and "only" as well?

My intuition tells me thus:
"He barely touched the ceiling, didn't he?" (He touched it however much it was. Whether he touched it or not is important)
"He barely spent time with his children over the weekends, did he?" (He nearly didn't spend time with them. The quality is looked upon. Spending a small amount of time does not count; thus this sentence is a negative)

How should you go about "only"?
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The same with 'only', certainly: He only ate one sandwich, didn't he?
I would say that these are invariable. You can't do an affirmative tag one time and a negative tag another time on the basis of any microscopic analysis of the meaning.

You [hardly / barely / scarcely] [ate any lunch / touched the ceiling / spent any time with your children], did you?

You only [ate lunch / touched the ceiling / spent some time with your children], didn't you?

CJ
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CalifJimYou [hardly / barely / scarcely] [ate any lunch / touched the ceiling / spent any time with your children], did you?
Tags for affirmative sentences with 'barely' --- you only use affirmative tags. However, I think you use two different replies of saying you did the same, depending if you mean affirmative or negative.

You barely touched the ceiling. So did I. (You touched it whether it be a lot or just a little)

You barely spent any time with your children over the weekend. Neither did I. (This is almost equal to your not having spent any time at all with them. So it's negative in meaning)
CalifJimYou only [ate lunch / touched the ceiling / spent some time with your children], didn't you?
As far as the inversion of sentences with 'only' placed at the head, I think with only meaning merely you don't invert the sentence, do you?

You moved out with her only yesterday. >>> Only yesterday you moved out with her.

You moved out with only her. >>> With only her did you move out.
HSSYou moved out with her only yesterday. >>> Only yesterday you moved out with her.
If "only" here means "no other times than" or "no more times than," then it should be "Only yesterday did you move out with her. --- Just crossed my mind.
HSSYou barely touched the ceiling. So did I. (You touched it whether it be a lot or just a little)
This exchange seems strange to my ear. I suppose it's possible, but it seems a very subtle point. I don't think it's very natural to think of using barelythat way. Well, not for me, anyway. Emotion: smile
HSSAs far as the inversion of sentences with 'only' placed at the head, I think with only meaning merely you don't invert the sentence, do you?

I'm not sure what you mean by different meanings for the word only. The following are all possible.

You moved out with her only yesterday.
Only yesterday you moved out with her.

Only yesterday did you move out with her.

You moved out with only her.
You only moved out with her.
Only with her did you move out.
(Not, typically, With only her did you move out. That's rather awkward. only is generally placed before the prepositional phrase.)

Maybe you're thinking of only when it means except that or but? This is quite informal.

I wanted to drive to the supermarket this morning, only the car broke down, so I never got there.

CJ
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Hi, CJ.
CalifJim
HSSYou barely touched the ceiling. So did I. (You touched it whether it be a lot or just a little)
This exchange seems strange to my ear. I suppose it's possible, but it seems a very subtle point. I don't think it's very natural to think of using barely that way. Well, not for me, anyway.
Then you'd think it would be better with 'Neither did I,' wouldn't you? --- You barely touched the ceiling. Neither did I.

I derived the above in the quote from the sentence I came across:

Chris barely passed the exam. So did I.

What do you think is the difference. To me the two sentences are both affirmative. (You touched the ceiling. Chris passed the exam)
CalifJim
HSSAs far as the inversion of sentences with 'only' placed at the head, I think with only meaning merely you don't invert the sentence, do you?

I'm not sure what you mean by different meanings for the word only. The following are all possible.

You moved out with her only yesterday.
Only yesterday you moved out with her.

Only yesterday did you move out with her.

You moved out with only her.
You only moved out with her.
Only with her did you move out.
I was thinking when 'only' means 'merely,' you normally don't invert the sentence:
Only yesterday you moved out with her.
And when you mean 'no more than,' you do invert it:
Only yesterday did you move out with her.
CalifJimYou only moved out with her.
With this, you would usually mean either "You moved out with her, but nothing other than that," or "You merely moved out with her," wouldn't you?
CalifJim(Not, typically, With only her did you move out. That's rather awkward. only is generally placed before the prepositional phrase.)
You mean it's rather awkward if the prepositional phrase is at the head of the sentence, and if 'only' is plased between 'with' and 'her,' right?
You moved out with only her is okay, right?
How about You moved out with her only? It's okay, right?
Just wondering.

Hiro