I know that some people use this when they want to say that they have no idea about that particular thing. But the thing is that, in my case none of them are native English speakers. So I thought it's worth to ask if natives use That thing I don't know. Though, indeed, it sounds OK and some natives even use "That I don't know" in the same context.

Also, what about That one I don't know? Sounds like native English to my non-native ears :)

  • That one I don't know.
  • That thing I don't know.

Not (really) sure about that (one). I don't (really) know about that. Can't say about that (one) - are among those I've heard from natives.

...a helpful reference I found on this. Still I think the question is valid. Should I say "I don't know" or "That I don't know"?


1 Answer 1


You asked if they 'sounded native' so I am contributing my opinion;

Those two sentences do not sound native to my native ears. The only exception I could think of would be if you wanted to declare a few objects before stating to which category they belonged (i.e.: 'like' vs 'dislike'). You could say;

That one, that one,... and that one I like, that one and that one I dislike

But using a single item, it doesn't sound native to me. The only time I have heard that kind of wording (and those specific sentences in particular) was from non-native people.

As far as those sentences being 'properly acceptable', I don't think so - but that's not what you asked.

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