How can't you know that?

0To me, "How can you not know that?" sounds more natural -- I think it would be more easily understood in conversation.0-

0I think using "how can you not know that..." has a level of exaggerated, dramatic resonance that this expression needs. You're expressing astonishment and surprise, so you'd want to emphasise that by using "can you not" instead of "can't you".02br
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00As a comparison, think about "You're supposed to be Italian, aren't you? So how come you can't make spaghetti vongole?"

0 How 01b00is it possible02b00 that you don't know that? 0-

0Thank you very much 05002br
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00Maybe it is because you would stress "not", so the non-contracted version is more common. Maybe the contracted version would be ok in more relaxed situations, without much emphasis. Like "How can't you know what a matrix is, Rose? I thought you learned that a school..." - Here you are not really supposed to know what a matrix is, so mayb

0I've been thinking more about "how can't you know", and tonight I discussed it with my daughter, who is very good at analyzing language. She had an interesting interpretation that made sense to me once I gave it some thought. Here it is:02br
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01font00"How 01i00can't you know02i00 what 'dude' means" has a 01i00d

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01cite10Khoff12cite10... I discussed it with my daughter, who is very good at analyzing language. She had an interesting interpretation that made sense to me once I gave it some thought. 12br
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10 I think your daughter hit it right on the nose. [<:o)] 'Know' should be negated, not 'can'. 02

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01cite10Khoff12cite10(Also -- Kooyeen -- "spaghetti" may be plural in Italian, but in English we eat "it," not "them.")12br
10Oops, thanks Khoff. But that will be a difficult mistake to avoid, you know, spaghetti is one of "my" words. 15012br
10What you said about "how can't you" makes sense. Thank you. 151