In [[mathematics]], [[logic]], and [[formal system]]s, a '''primitive notion''' is an undefined concept. In particular, a primitive notion is not defined in terms of previously defined concepts, but is only motivated informally, usually by an appeal to [[Intuition (knowledge)|intuition]] and everyday experience. In an [[axiomatic theory]] or other [[formal system]], the role of a primitive notion is analogous to that of [[axiom]]. In axiomatic theories, the primitive notions are sometimes said to be "defined" by one or more axioms, but this can be misleading. Formal theories cannot dispense with primitive notions, under pain of [[infinite regress]].
==Details==
[[Alfred Tarski]] explained the role of primitive notions as follows:<ref>[[Alfred Tarski]] (1946) ''Introduction to Logic and the Methodology of the Deductive Sciences'', page 118, [[Oxford University Press]].</ref>