In mathematical logic, an elementary theory is a theory that involves axioms using only finitary first-order logic, without reference to set theory or using any axioms that have consistency strength equal to set theory.

Saying that a theory is elementary is a weaker condition than saying it is algebraic.

Examples

Examples of elementary theories include:

The theory of groups

• The theory of finite groups

• The theory of abelian groups

The theory of fields

• The theory of finite fields

• The theory of real closed fields

• Axiomization of Euclidean geometry

Related

• Elementary definition

• Elementary theory of the reals

References

• Mac Lane and Moerdijk, Sheaves in Geometry and Logic: A First Introduction to Topos Theory, page 4.