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When asked whether he recognized equal rights of atheists, George H. W. Bush said1:

No, I don't know that atheists should be considered as citizens, nor should they be considered patriots. This is one nation under God.

I would understand if he had used another verb:

No, I don't think/believe that atheists should be considered...

I would also understand if he had chosen another conjunction:

No, I don't know if atheists should be considered...

Is the original quoted sentence grammatically correct? Is it common to use know in the sense of think? Or is this some dialect-specific meaning? Could you please give some more examples of this usage of know?

1 Wikipedia source

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up vote 6 down vote accepted

The string I don't know that is grammatical and common and is used to express doubt. The use of subordinators if or whether after know would suggest a less firm position: he doesn't know or he's not so certain.

  • I don't know that there are bargains yet, but there certainly are opportunities.
  • I don't know that the President has said that he fully supports the conference of the states
  • I don't know that his chances are any better now than they were then
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Could I say: "I don't know that he is a competent professional."? – Armen Ծիրունյան Feb 2 '12 at 21:27
Yes, especially if the stress was on competent. It would commonly be followed by something like, "but he has passed the licensing tests." – Brett Reynolds Feb 2 '12 at 21:36
Could I ask you to update your answer with a couple of typical sentences with this meaning of know, please? – Armen Ծիրունյան Feb 2 '12 at 21:38
I've added a few, but if you click on the link, and then click on the result, it will give you thousands of relevant examples (mixed in with some non-relevant ones.) – Brett Reynolds Feb 2 '12 at 21:52
Thank you very much! – Armen Ծիրունյան Feb 2 '12 at 21:56

Yes, it is grammatically correct, albeit informal. It is an idiomatic use of the verb know, meaning I have doubts about somebody's ability to do something. The entry in the Oxford Dictionaries Online reads as follows:

not know that (informal) used to express one’s doubts about one’s ability to do something: I don’t know that I can sum up my meaning on paper.

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Do you have any reference or basis for your claim that this usage is "informal" and/or "idiomatic"? To the contrary, the first meaning of know in wiktionary is neither informal nor idiomatic: "To be certain or sure about. (eg) I know that I’m right and you’re wrong", from which "don't know" means uncertain, unsure. – jwpat7 Feb 2 '12 at 21:56
@jwpat7: If you follow the link of my answer to Oxford Dictionary, you will see the reference for my claim. Just scroll down to the phrases listed until you reach not know that (informal) used to express one’s doubts about one’s ability to do something: I don’t know that I can sum up my meaning on paper – Irene Feb 3 '12 at 13:25
Will you add that into your answer? – jwpat7 Feb 3 '12 at 14:52
@jwpat7: I just edited my answer per your instructions. – Irene Feb 3 '12 at 19:46

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