Page "Naive set theory" Paragraph 2

In the sense of this article, a naive theory is a non-formalized theory, that is, a theory that uses a natural language to describe sets.

The words and, or, if ... then, not, for some, for every are not subject to rigorous definition.

It is useful to study sets naively at an early stage of mathematics in order to develop facility for working with them.

Furthermore, a firm grasp of set theoretical concepts from a naive standpoint is important as a first stage in understanding the motivation for the formal axioms of set theory.