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Gödel's Incompleteness Theorems

Kurt Gödel · 1931

"Any formal system powerful enough to describe arithmetic contains true statements it can never prove, and it can't even prove its own consistency."

The idea

Gödel was 25 when he proved something unsettling about mathematics: any system rich enough to do arithmetic will always contain true statements it can't prove from within.

Why it works

Gödel's first theorem shows any consistent formal system capable of arithmetic contains true statements it can neither prove nor disprove — completeness and consistency can't both be had. His second theorem goes further: such a system can't prove its own consistency without stepping outside itself, by encoding 'this statement is unprovable' directly into arithmetic.

The takeaway — recall it first
Check your understanding

What does Gödel's second incompleteness theorem say a consistent formal system capable of arithmetic can never do?

Further reading

Read more about the topic

The explanation above is written with AI assistance. These are the originals — go to them to check it.

  • Gödel's Incompleteness TheoremsStanford Encyclopedia of Philosophy
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