# Predicate logic

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In mathematical logic, **predicate logic** is the generic term for symbolic formal systems like first-order logic, second-order logic, many-sorted logic, or infinitary logic. This formal system is distinguished from other systems in that its formulae contain variables which can be quantified. Two common quantifiers are the existential ∃ ("there exists") and universal ∀ ("for all") quantifiers. The variables could be elements in the universe under discussion, or perhaps relations or functions over that universe. For instance, an existential quantifier over a function symbol would be interpreted as modifier "there is a function". The foundations of predicate logic were developed independently by Gottlob Frege and Charles Peirce.^{[1]}

In informal usage, the term "predicate logic" occasionally refers to first-order logic. Some authors consider the **predicate calculus** to be an axiomatized form of predicate logic, and the predicate logic to be derived from an informal, more intuitive development.^{[2]}

Predicate logics also include logics mixing modal operators and quantifiers. See Modal logic, Saul Kripke, Barcan Marcus formulae, A. N. Prior, and Nicholas Rescher.

## See also

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## Footnotes

- ↑ Eric M. Hammer: Semantics for Existential Graphs,
*Journal of Philosophical Logic*, Volume 27, Issue 5 (October 1998), page 489: "Development of first-order logic independently of Frege, anticipating prenex and Skolem normal forms" - ↑ Among these authors is Stolyar, p. 166. Hamilton considers both to be calculi but divides them into an informal calculus and a formal calculus.

## References

- A. G. Hamilton 1978,
*Logic for Mathematicians*, Cambridge University Press, Cambridge UK ISBN 0-521-21838-1 - Abram Aronovic Stolyar 1970,
*Introduction to Elementary Mathematical Logic*, Dover Publications, Inc. NY. ISBN 0-486-645614 - George F Luger,
*Artificial Intelligence*, Pearson Education, ISBN 978-81-317-2327-2 - {{#invoke:citation/CS1|citation

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