**Set theory** is the branch of mathematics that studies sets, which are collections of objects. Although any type of object can be collected into a set, set theory is applied most often to objects that are relevant to mathematics. The language of set theory can be used in the definitions of nearly all mathematical objects.

The modern study of set theory was initiated by Georg Cantor and Richard Dedekind in the 1870s. After the discovery of paradoxes in naive set theory, numerous axiom systems were proposed in the early twentieth century, of which the Zermeloâ€“Fraenkel axioms, with the axiom of choice, are the best-known.

Set theory is commonly employed as a foundational system for mathematics, particularly in the form of Zermeloâ€“Fraenkel set theory with the axiom of choice. Beyond its foundational role, set theory is a branch of mathematics in its own right, with an active research community. Contemporary research into set theory includes a diverse collection of topics, ranging from the structure of the real number line to the study of the consistency of large cardinals.

Read more about Set Theory: History, Basic Concepts, Some Ontology, Axiomatic Set Theory, Applications, Objections To Set Theory As A Foundation For Mathematics

### Famous quotes containing the words set and/or theory:

“They *set* up a noise like crickets,

A chattering wise and sweet,

And her hair was a folded flower

And the quiet of love in her feet.”

—William Butler Yeats (1865–1939)

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—Rheta Childe Dorr (1866–1948)