more on this theme     |     more from this thinker


Single Idea 13366

[filed under theme 5. Theory of Logic / L. Paradox / 5. Paradoxes in Set Theory / c. Burali-Forti's paradox ]

Full Idea

Burali-Forti: φ(x) is 'x is an ordinal', and so w is the set of all ordinals, On; δ(x) is the least ordinal greater than every member of x (abbreviation: log(x)). The contradiction is that log(On)∈On and log(On)∉On.

Gist of Idea

The least ordinal greater than the set of all ordinals is both one of them and not one of them

Source

Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §2)

Book Ref

-: 'Mind' [-], p.27


The 8 ideas from 'The Structure of Paradoxes of Self-Reference'

The least ordinal greater than the set of all ordinals is both one of them and not one of them [Priest,G]
The next set up in the hierarchy of sets seems to be both a member and not a member of it [Priest,G]
The 'least indefinable ordinal' is defined by that very phrase [Priest,G]
'x is a natural number definable in less than 19 words' leads to contradiction [Priest,G]
By diagonalization we can define a real number that isn't in the definable set of reals [Priest,G]
If you know that a sentence is not one of the known sentences, you know its truth [Priest,G]
There are Liar Pairs, and Liar Chains, which fit the same pattern as the basic Liar [Priest,G]
Typically, paradoxes are dealt with by dividing them into two groups, but the division is wrong [Priest,G]