Single Idea 13800

[catalogued under 5. Theory of Logic / D. Assumptions for Logic / 4. Identity in Logic]

Full Idea

We usually take these two principles together as the basic principles of identity: |= α=α and α=β |= φ(α/ξ) ↔ φ(β/ξ). The second (with scant regard for history) is known as Leibniz's Law.

Gist of Idea

|= α=α and α=β |= φ(α/ξ ↔ φ(β/ξ) fix identity

Source

David Bostock (Intermediate Logic [1997], 8.1)

Book Reference

Bostock,David: 'Intermediate Logic' [OUP 1997], p.324

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