---
tag: XSZGB47B6Y
kind: concept
name: Abstraction principle
sources:
  - wikipedia: en:76765067@r1368301704
    locator: Glossary of logic, section A
    note: adopted
    mention: wikipedia://en/76765067#OV9C
    sections: [Summary]
inventory: [7QY9ZYB2PK]
---

## Summary

A formula of the form (∀α)(∀β)(Abst(α) = Abst(β) ↔ Equ(α, β)), where Abst is an abstraction operator mapping the type of entities ranged over by α and β to objects, and “Equ” is an equivalence relation on the type of entities ranged over by α and β. For instance, Hume's principle, and Basic Law V.