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A double negative is a construction occurring when two forms of grammatical negation are used in the same sentence. This is typically used to convey a different shade of meaning from a strictly positive sentence ("You're not unattractive" vs "You're attractive").
In propositional logic, the double negation of a statement states that "it is not the case that the statement is not true". In classical logic, every statement is logically equivalent to its double negation, but this is not true in intuitionistic logic; this can be expressed by the formula A ≡ ~(~A) where the sign ≡ expresses logical equivalence and the sign ~ expresses negation.
In logic, a rule of replacement [1] [2] [3] is a transformation rule that may be applied to only a particular segment of an expression.A logical system may be constructed so that it uses either axioms, rules of inference, or both as transformation rules for logical expressions in the system.
A set of rules can be used to infer any valid conclusion if it is complete, while never inferring an invalid conclusion, if it is sound. A sound and complete set of rules need not include every rule in the following list, as many of the rules are redundant, and can be proven with the other rules.
(Rhetorically, this becomes the device of litotes; it can be difficult to distinguish litotes from pleonastic double negation, a feature which may be used for ironic effect.) Although the use of "double negatives" for emphatic purposes is sometimes discouraged in standard English, it is mandatory in other languages like Spanish or French.
Expletive negation is a term that originated in French language studies. It refers to a sentence construction that contains one or more negations that, from a modern perspective, seem superfluous. An example is the "double-negative" in: "Nobody never lifted a finger to help her."
A negation is a negative polarity item, abbreviated NPI or NEG. The linguistic environment in which a polarity item appears is a licensing context. In the simplest case, an affirmative statement provides a licensing context for a PPI, while negation provides a licensing context for an NPI. However, there are many complications, and not all ...
A double negation does not affirm the law of the excluded middle ; while it is not necessarily the case that PEM is upheld in any context, no counterexample can be given either. Such a counterexample would be an inference (inferring the negation of the law for a certain proposition) disallowed under classical logic and thus PEM is not allowed ...