Models, completeness and incompleteness
Semantic consequence and arithmetic completeness are distinct.
Key knowledge
A first-order model interprets a theory's sentences as true. Soundness and completeness equate derivability with truth in every model. A consistent effectively axiomatized extension of Peano arithmetic nevertheless leaves some arithmetic sentence and its negation unprovable.
Conditions and scope
- Use a countable first-order language and classical proof rules; the arithmetic limitation assumes effective axiomatization and consistency.
- Truth in all models is distinct from truth in one intended model; no claim about all human knowledge follows.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Sections 7.2–7.6: structures, assignments and quantifiers; section 9: soundness/completeness. Physical pages 83–100, 128–133 and 152–153. Section V: logically adequate strengthening of TNT/PA, consistency and Gödel–Rosser incompleteness; appendix C identifies TNT with PA.
2026-10-10 · Model semantics and scoped Gödel–Rosser limitation; no new proof certification.
Entry details
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- math-formal-models-incompleteness
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