Is there any difference between saying "I am not really sure where the noise is from" and "I am really not sure where the noise is from"? are they interchangeable?

  • In your example, they are interchangeable - but "I am not really sure" is probably more correct than the idiomatic: "I'm really not sure."
    – Oldbag
    May 28, 2015 at 10:58

1 Answer 1


There is a difference between the two:

I am not [really sure]

You're anywhere between almost completely sure and quite unsure. Really amplifies sure, and really sure means you's as good as completely, totally sure. The not just says you're not that sure yet, or even that you are not that sure at all. The exact amount of uncertainty depends on many things like context and intonation. I suspect a difference between BrE and AmE as well (cf "quite").

I am really [not sure]

You're not sure at all! Here, really amplifies not sure. While not sure implies you have doubts, really makes that stronger: you have serious doubts.

Another, slightly different example would be:

I am not completely happy.

Meaning you're happy, but not 100%.

On the other hand, if you change the order (and replace "not happy" with the more natural "unhappy"):

I am completely unhappy.

Means that you are almost completely unsatisfied; that is almost the opposite of the first version.

  • 2
    You've got the second one right. But the first 'not really sure' means you're vaguely unsure. Literally you're not absolutely certain, but that leaves a broad range of uncertainty, only slightly or very unsure.
    – Mitch
    May 28, 2015 at 11:20
  • 1
    Yeah, I have the same thoughts about the first -- generally it means that there is a fair amount of uncertainty.
    – Hot Licks
    May 28, 2015 at 11:36
  • @Mitch: I added some extra nuance to option 1. I think it depends largely on context. I suspect that especially in BrE "not really sure" may well mean "no way in hell". ("You want me to go skinny dipping in mid winter? I'm not really sure that's such a great idea.")
    – oerkelens
    May 28, 2015 at 12:58
  • @oerkelens there's a lot of pragmatics here, understatement, 'Not really sure' may be a nice way of saying 'No, but I feel bad saying that outright', and 'really not sure' means 'I can't believe you're thinking of bungie jumping what with your hernia, but you're responsible for your own hospital bills'
    – Mitch
    May 28, 2015 at 13:02
  • 2
    This rings true for me. I would say "I'm not really sure" if I'm expressing doubt and "I'm really not sure" if I'm trying to get someone to stop asking me for my stance on something. May 28, 2015 at 13:27

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