Basic Law V

E101761

Basic Law V is a central axiom in Frege’s logical system that equates the extensions of concepts with identical truth conditions, and whose inconsistency famously undermined his logicist foundation for arithmetic.

All labels observed (1)

Label Occurrences
Basic Law V canonical 3

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Statements (48)

Predicate Object
instanceOf axiom schema
logical axiom
principle in the philosophy of mathematics
aimedToJustify definition of numbers as extensions of concepts
alsoWrittenAs ∀F∀G(εF = εG ↔ ∀x(Fx ↔ Gx))
appliesTo first-level concepts
second-level concepts
author Gottlob Frege
category abstraction principle for concepts
centralIn Frege’s system in "Grundgesetze der Arithmetik"
surface form: Frege's logicist program
concerns extensions of concepts
criticizedBy Bertrand Russell
later neo-logicists
discussedIn Grundgesetze der Arithmetik, Volume II
surface form: Frege's Appendix to Grundgesetze der Arithmetik, Volume II
equates extensions of coextensive concepts
extensions of concepts with identical truth conditions
expresses that concepts with the same extension have the same course-of-values
formalizes principle of extensionality for concepts
historicalImpact influenced axiomatic set theory
motivated development of type theory
triggered revisions of logic and set theory
inconsistencyDiscoveredIn 1902
involves biconditional relating extension identity and coextensiveness
identity of extensions
isInconsistentWith naive set-theoretic reasoning
unrestricted comprehension for concepts
leadsTo Russell’s paradox
surface form: Russell's paradox
logicalForm abstraction principle
partOf Frege's logical system
Grundgesetze der Arithmetik, Volume II
surface form: Grundgesetze der Arithmetik
publicationYear 1893
relatedTo Axiom of Extensionality in set theory
naive comprehension schema
requires second-order quantification over concepts
roleIn derivation of arithmetic from logic
statedIn Frege’s system in "Grundgesetze der Arithmetik"
surface form: Grundgesetze der Arithmetik, Volume I
statusInModernLogic known to be inconsistent with second-order logic plus full comprehension
studiedIn foundations of arithmetic
history of logic
philosophy of mathematics
symbolicallyFormulatedAs ∀F∀G(Ext(F) = Ext(G) ↔ ∀x(Fx ↔ Gx))
undermined Frege's original logicist foundation for arithmetic
usesNotion course-of-values
extension of a concept
wasShownInconsistentBy Bertrand Russell
weakenedVariantsInclude Hume’s Principle (derivable, not postulated)
surface form: Hume's Principle

predicative restrictions on abstraction principles
weakenedVariantsUsedIn neo-logicism

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Referenced by (3)

Full triples — surface form annotated when it differs from this entity's canonical label.