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Possible Duplicate:
Is “not eating or drinking” equal to “not eating or not drinking”?

I am confused in inferring a sentence of pattern "X is not Y or Z".

Is it the same as "X is not Y or X is not Z" ?

OR

Is it the same as "X is not Y or X is Z" ?

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  • J D is correct, applying the rule of that post here states that "X is not Y or Z" corresponds to "X is not Y or X is not X". In symbolic logic where n corresponds to not, we have X=n(Y v Z) if and only if X=nY ^ nZ. This is referred to as one of De-Morgan's Laws.
    – BBischof
    Oct 13, 2010 at 5:56
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    But "not X or Y" =/= not (X or Y), right? Oct 13, 2010 at 6:26
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    You can't use the rules of logic "and", "not, "or" to English. "Didn't you beat your wife?" "No!". The answerer is saying he did not beat his wife. If you used the negation from logic, the answerer would be denying he didn't, meaning he did. Oct 13, 2010 at 9:55
  • Martinho is exactly right, and this is the reason for the confusion of your comment. Notice in my comment I use parenthesis. It is for exactly this reason! However, now I think you get the idea.
    – BBischof
    Oct 13, 2010 at 18:51

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Language only partly follows the rules of logic: there are other dimensions, most importantly that of pragmatics.

"X is not Y or Z"

is formally ambiguous, and in certain contexts, or in certain tones of voice, it might mean one of your examples. But the normal pragmatic meaning is "X is neither Y nor Z", or expanding, "X is not Y and X is not Z".

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  • This is not easy to answer in the abstract, i.e., with no context and using variables (X, Y, Z) instead of actual words or qualities. Are we supposed to be thinking of nouns? classes or individuals? adjectives? Part of the problem is that "is" does not always mean "equals" in English, but often means "is included in". So "X is Y" often means not that X and Y mean the same thing, but that anything which is an X is also a Y (or anything which is X is also Y, or X has the quality Y, or ...) So it's better to look at specific instances, not abstrations. Jun 6, 2011 at 4:31

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