Ideas from 'The Structure of Paradoxes of Self-Reference' by Graham Priest [1994], by Theme Structure

[found in 'Mind' (ed/tr -) [- ,]].

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5. Theory of Logic / L. Paradox / 1. Paradox
Typically, paradoxes are dealt with by dividing them into two groups, but the division is wrong
                        Full Idea: A natural principle is the same kind of paradox will have the same kind of solution. Standardly Ramsey's first group are solved by denying the existence of some totality, and the second group are less clear. But denial of the groups sink both.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §5)
                        A reaction: [compressed] This sums up the argument of Priest's paper, which is that it is Ramsey's division into two kinds (see Idea 13334) which is preventing us from getting to grips with the paradoxes. Priest, notoriously, just lives with them.
5. Theory of Logic / L. Paradox / 4. Paradoxes in Logic / b. König's paradox
The 'least indefinable ordinal' is defined by that very phrase
                        Full Idea: König: there are indefinable ordinals, and the least indefinable ordinal has just been defined in that very phrase. (Recall that something is definable iff there is a (non-indexical) noun-phrase that refers to it).
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §3)
                        A reaction: Priest makes great subsequent use of this one, but it feels like a card trick. 'Everything indefinable has now been defined' (by the subject of this sentence)? König, of course, does manage to pick out one particular object.
5. Theory of Logic / L. Paradox / 4. Paradoxes in Logic / c. Berry's paradox
'x is a natural number definable in less than 19 words' leads to contradiction
                        Full Idea: Berry: if we take 'x is a natural number definable in less than 19 words', we can generate a number which is and is not one of these numbers.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §3)
                        A reaction: [not enough space to spell this one out in full]
5. Theory of Logic / L. Paradox / 4. Paradoxes in Logic / d. Richard's paradox
By diagonalization we can define a real number that isn't in the definable set of reals
                        Full Idea: Richard: φ(x) is 'x is a definable real number between 0 and 1' and ψ(x) is 'x is definable'. We can define a real by diagonalization so that it is not in x. It is and isn't in the set of reals.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §3)
                        A reaction: [this isn't fully clear here because it is compressed]
5. Theory of Logic / L. Paradox / 5. Paradoxes in Set Theory / c. Burali-Forti's paradox
The least ordinal greater than the set of all ordinals is both one of them and not one of them
                        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.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §2)
5. Theory of Logic / L. Paradox / 5. Paradoxes in Set Theory / e. Mirimanoff's paradox
The next set up in the hierarchy of sets seems to be both a member and not a member of it
                        Full Idea: Mirimanoff: φ(x) is 'x is well founded', so that w is the cumulative hierarchy of sets, V; &delta(x) is just the power set of x, P(x). If x⊆V, then V∈V and V∉V, since δ(V) is just V itself.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §2)
5. Theory of Logic / L. Paradox / 6. Paradoxes in Language / a. The Liar paradox
There are Liar Pairs, and Liar Chains, which fit the same pattern as the basic Liar
                        Full Idea: There are liar chains which fit the pattern of Transcendence and Closure, as can be seen with the simplest case of the Liar Pair.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §4)
                        A reaction: [Priest gives full details] Priest's idea is that Closure is when a set is announced as complete, and Transcendence is when the set is forced to expand. He claims that the two keep coming into conflict.
If you know that a sentence is not one of the known sentences, you know its truth
                        Full Idea: In the family of the Liar is the Knower Paradox, where φ(x) is 'x is known to be true', and there is a set of known things, Kn. By knowing a sentence is not in the known sentences, you know its truth.
                        From: Graham Priest (The Structure of Paradoxes of Self-Reference [1994], §4)
                        A reaction: [mostly my wording]