necessary(redirected from Necessary (logic))
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a. (of a statement, formula, etc.) true under all interpretations or in all possible circumstances
b. (of a proposition) determined to be true by its meaning, so that its denial would be self-contradictory
c. (of a property) essential, so that without it its subject would not be the entity it is
d. (of an inference) always yielding a true conclusion when its premises are true; valid
e. (of a condition) entailed by the truth of some statement or the obtaining of some state of affairs
2. Philosophy (in a nonlogical sense) expressing a law of nature, so that if it is in this sense necessary that all As are B, even although it is not contradictory to conceive of an A which is not B, we are licensed to infer that if something were an A it would have to be B