more on this theme     |     more from this text

Single Idea 10879

[filed under theme 4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / j. Axiom of Choice IX ]

Full Idea

Axiom of Choice: For every set we can provide a mechanism for choosing one member of any non-empty subset of the set.

Gist of Idea

Choice: For every set a mechanism will choose one member of any non-empty subset

Source

Brian Clegg (Infinity: Quest to Think the Unthinkable [2003], Ch.15)

Book Ref

Clegg,Brian: 'Infinity' [Robinson 2003], p.206

A Reaction

This axiom is unusual because it makes the bold claim that such a 'mechanism' can always be found. Cohen showed that this axiom is separate. The tricky bit is choosing from an infinite subset.

The 20 ideas from Brian Clegg

10854 Transcendental numbers can't be fitted to finite equations [Clegg]
10853 Either lack of zero made early mathematics geometrical, or the geometrical approach made zero meaningless [Clegg]
10858 By adding an axis of imaginary numbers, we get the useful 'number plane' instead of number line [Clegg]
10861 Beyond infinity cardinals and ordinals can come apart [Clegg]
10860 An ordinal number is defined by the set that comes before it [Clegg]
10859 A set is 'well-ordered' if every subset has a first element [Clegg]
10857 Set theory made a closer study of infinity possible [Clegg]
10864 Any set can always generate a larger set - its powerset, of subsets [Clegg]
10862 The 'continuum hypothesis' says aleph-one is the cardinality of the reals [Clegg]
10866 Cantor's account of infinities has the shaky foundation of irrational numbers [Clegg]
10869 The Continuum Hypothesis is independent of the axioms of set theory [Clegg]
10872 Extensionality: Two sets are equal if and only if they have the same elements [Clegg]
10874 Specification: a condition applied to a set will always produce a new set [Clegg]
10877 Powers: All the subsets of a given set form their own new powerset [Clegg]
10879 Choice: For every set a mechanism will choose one member of any non-empty subset [Clegg]
10871 Axiom of Existence: there exists at least one set [Clegg]
10878 Infinity: There exists a set of the empty set and the successor of each element [Clegg]
10875 Pairing: For any two sets there exists a set to which they both belong [Clegg]
10876 Unions: There is a set of all the elements which belong to at least one set in a collection [Clegg]
10880 Mathematics can be 'pure' (unapplied), 'real' (physically grounded); or 'applied' (just applicable) [Clegg]