'Can't say' vs. 'can't tell'

May both expressions mean either 'don't know' or 'be not allowed to share the information'?

Or only 'can't tell' means 'don't know' while 'can't say' means 'be unwilling to reveal'?


'I can't tell/say if he's been hurt. I really have no idea.'

'I can't tell/say. I am sworn to secrecy.'

I am also aware that 'can't say' may mean 'realize/'must admit' like in the sentence 'I can't say I have not been warned.' However, this is not my question here.

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    I would say that both expressions can have either sense. However, in the first sense "Can't say" is more of a dismissive, shrug-of-the-shoulders "Don't know" while "I can't tell" implies that I have tried to find out but was unable to form an opinion. Apr 16, 2017 at 7:50
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    @KateBunting - Right, while I could say, “I can’t tell from from here if she’s got her book,” “can’t say from here” doen’t quite work.
    – Jim
    Apr 16, 2017 at 15:54
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    Let's not forget the variable of physical location, which is implied in the comment left by @Jim. "I can't tell if she's got her book" could mean that I'm too far away to see is she has her book, or that she just slipped around the corner and out of my line of vision. Eyesight also factors into not being able to tell, as in "I can't tell if the word in that sign a couple hundred feet away is 'but' or 'nut'." Apr 16, 2017 at 23:55

1 Answer 1


First of all, you are asking two questions in one. The first being the difference between can't say/can't tell in the first example, the second being the difference between being unable due to lack of knowledge vs prohibition (the second example).

In the first case (lack of knowledge), the difference is:

He may or may not be injured, but I can't tell.

You have not been able to glean any information yourself. You just don't know.

I think he might be injured, but I can't say for sure.

You may have some idea, but you cannot say with confidence.

In the second case (prohibition):

I can't say, I promised.

The normal usage, means what you expect - I am prohibited from saying/revealing that information.

I can't tell, I promised.

I would say this is incorrect in the case of prohibition - I have never heard it used in this way. This would be probably misinterpreted to mean some other valid use of "tell", such as:

I can't tell her, I promised.

In this case, tell means to "say to someone else".

I can't tell on her, I promised.

This has a completely different meaning based on a completed different definition of tell - to "tell on" - to reveal the wrongdoing of someone else to an authority. I.e. a full sentence might be:

Who stole your Apple?
It was Elise.
You should report her to the teacher!
I can't tell on her, I promised.

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