Second Order Logic Second-order logic is the extension of first-order logic obtained by introducing quantification of predicate and function variables. A first-order formula, say Fxy, may be converted to a second-order formula by replacing F with a...

Logic, Non-Classical The purpose of this entry is to survey those modern logics that are often called "non-classical," classical logic being the theory of validity concerning truth functions and first-order quantifiers likely to be found...

In logic and mathematics second-order logic is an extension of first-order logic, which itself is an extension of propositional logic.[1] Second-order logic is in turn extended by higher-order logic and type theory. Both first-order and second-order...