The result of negating the negation of a proposition, and the principle (not admitted in intuitionist logic) that this is equivalent to the proposition itself.
〔哲〕否定之否定
Example sentencesExamples
One reason has to do with the common (natural language) reasoning involving counter-logicals, including, for example, sentences such as ‘If intuitionistic logic is correct, then double negation elimination is invalid’.
Thus, the double negation nPn is established when one shows that an assumption nPn is contradictory.
And so, classical logic is seen to be a fragment of intuitionist logic and obtains a legitimate, if virtual, existence, in the shadow world of double negations, a compelling picture.