**Zeroth-order logic** is first-order logic without variables or quantifiers. Some authors use the phrase "zeroth-order logic" as a synonym for the propositional calculus,^{[1]} but an alternative definition extends propositional logic by adding constants, operations, and relations on non-Boolean values.^{[2]} Every zeroth-order language in this broader sense is complete and compact.^{[2]}

## References

**^**Andrews, Peter B. (2002),*An introduction to mathematical logic and type theory: to truth through proof*, Applied Logic Series,**27**(Second ed.), Kluwer Academic Publishers, Dordrecht, p. 201, doi:10.1007/978-94-015-9934-4, ISBN 1-4020-0763-9, MR 1932484.- ^
^{a}^{b}Tao, Terence (2010), "1.4.2 Zeroth-order logic",*An epsilon of room, II*, American Mathematical Society, Providence, RI, pp. 27–31, doi:10.1090/gsm/117, ISBN 978-0-8218-5280-4, MR 2780010.