<logic, semantics> a sentence, proposition, thought, or judgement is necessary if it is true of any possible world. Some philosophers (e.g. A.J. Ayer) maintain that the truths of logic and mathematics are necessary because they are a priori, and a priori simply because they are analytic; similarly maintaining that contigent, a posteriori, and asynthetic are equivalent.
[A Philosophical Glossary]
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