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6. Mathematics / B. Foundations for Mathematics / 3. Axioms for Number / g. Incompleteness of Arithmetic

[discovery that axioms can't prove all truths of arithmetic]

20 ideas
There is a sentence which a theory can show is true iff it is unprovable [Smith,P on Gödel]
First Incompleteness: arithmetic must always be incomplete [Smith,P on Gödel]
Arithmetical truth cannot be fully and formally derived from axioms and inference rules [Nagel/Newman on Gödel]
First Incompleteness: a decent consistent system is syntactically incomplete [George/Velleman on Gödel]
Second Incompleteness: a decent consistent system can't prove its own consistency [George/Velleman on Gödel]
'This system can't prove this statement' makes it unprovable either way [Clegg on Gödel]
Some arithmetical problems require assumptions which transcend arithmetic [Gödel]
Gödel eventually hoped for a generalised completeness theorem leaving nothing undecidable [Gödel]
The real reason for Incompleteness in arithmetic is inability to define truth in a language [Gödel]
Gentzen proved the consistency of arithmetic from assumptions beyond arithmetic [Musgrave on Gentzen]
Intuitionists find the Incompleteness Theorem unsurprising, since proof is intuitive, not formal [Dummett]
Incompleteness results in arithmetic from combining addition and successor with multiplication [Smith,P]
Multiplication only generates incompleteness if combined with addition and successor [Smith,P]
Gödel showed that arithmetic is either incomplete or inconsistent [Rey]
It is only 2nd-order isomorphism which suggested first-order PA completeness [Mayberry]
The incompletability of formal arithmetic reveals that logic also cannot be completely characterized [Hale/Wright]
The Incompleteness proofs use arithmetic to talk about formal arithmetic [George/Velleman]
Arithmetical undecidability is always settled at the next stage up [Koellner]
Gödel's Second says that semantic consequence outruns provability [Hanna]
We can add Reflexion Principles to Peano Arithmetic, which assert its consistency or soundness [Halbach]