# Is there a One True Set Theory?

Logically, no. Set theory is just one of many first-order theories. Other theories can be defined independently of set theory. For example, Euclidean geometry and group theory are two first-order theories that can be defined without any mention of sets.

## Is set theory real?

So, the essence of set theory is the study of infinite sets, and therefore it can be defined as the mathematical theory of the actual—as opposed to potential—infinite. The notion of set is so simple that it is usually introduced informally, and regarded as self-evident.

## Is naive set theory still used?

The term naive set theory is still today also used in some literature to refer to the set theories studied by Frege and Cantor, rather than to the informal counterparts of modern axiomatic set theory.

## What is Cantor’s set theory?

Cantor’s theorem, in set theory, the theorem that the cardinality (numerical size) of a set is strictly less than the cardinality of its power set, or collection of subsets. In symbols, a finite set S with n elements contains 2n subsets, so that the cardinality of the set S is n and its power set P(S) is 2n.

## Why there is no set of all sets?

Reasons for nonexistence. Many set theories do not allow for the existence of a universal set. For example, it is directly contradicted by the axioms such as the axiom of regularity and its existence would imply inconsistencies. The standard Zermelo–Fraenkel set theory is instead based on the cumulative hierarchy.