### Single Idea 9539

#### [catalogued under 4. Formal Logic / B. Propositional Logic PL / 5. Completeness of PL]

Full Idea

A logical system is complete is all expressions of a specified kind are derivable in it. If we specify tautologous sequent-expressions, then propositional logic is complete, because we can show that all tautologous sequents are derivable.

Gist of Idea

Propositional logic is complete, since all of its tautologous sequents are derivable

Source

E.J. Lemmon (Beginning Logic [1965], 2.5)

Book Reference

Lemmon,E.J.: 'Beginning Logic' [Nelson 1979], p.90

A Reaction

[See Lemmon 2.5 for details of the proofs]