more on this theme     |     more from this text

---

Single Idea 13851

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

Full Idea

Unlike ∨, →, ↔, and ∀, the sign = is not eliminable from a logic.

Clarification

=

Gist of Idea

Unlike most other signs, = cannot be eliminated

Source

Engelbretsen,G/Sayward,C (Philosophical Logic: Intro to Advanced Topics [2011], Ch.3)

Book Ref

Engelbretsen,G/Sayward,C: 'Philosophical Logic: Intro to Advanced Topics' [Continuum 2011], p.70

---

The 8 ideas from Engelbretsen,G/Sayward,C

13849

Classical logic rests on truth and models, where constructivist logic rests on defence and refutation [Engelbretsen/Sayward]

13852

Axioms are ω-incomplete if the instances are all derivable, but the universal quantification isn't [Engelbretsen/Sayward]

13915

Syllogistic can't handle sentences with singular terms, or relational terms, or compound sentences [Engelbretsen/Sayward]

13913

The four 'perfect syllogisms' are called Barbara, Celarent, Darii and Ferio [Engelbretsen/Sayward]

13914

Syllogistic logic has one rule: what is affirmed/denied of wholes is affirmed/denied of their parts [Engelbretsen/Sayward]

13916

Term logic uses expression letters and brackets, and '-' for negative terms, and '+' for compound terms [Engelbretsen/Sayward]

13850

In modern logic all formal validity can be characterised syntactically [Engelbretsen/Sayward]

13851

Unlike most other signs, = cannot be eliminated [Engelbretsen/Sayward]