Definition:Undefined Term

Definition
For a definition to not be circular, the definer must use already defined terms.

However, this process cannot go on indefinitely. If we were to insist on everything being defined only using previously defined terms, we would enter an infinite regress.

Concepts that are not defined in terms of previously defined concepts are called undefined terms, primitive terms, or primitive notions.

An undefined term is frequently explained by using an ostensive definition: that is, a statement that shows what something is, rather than explains.

Also see

 * Axiom
 * Set


 * Ostensive Definition