Ideas from 'An Introduction to Modal Logic' by GE Hughes/M Cresswell [1968], by Theme Structure
[found in 'An Introduction to Modal Logic' by Hughes,G./Cresswell,M. [Methuen 1972,416294707]].
Click on the Idea Number for the full details 
back to texts

expand these ideas
4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / b. Terminology of PL
9540

A 'valueassignment' (V) is when to each variable in the set V assigns either the value 1 or the value 0

4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL
9541

The Law of Transposition says (P→Q) → (¬Q→¬P)

4. Formal Logic / B. Propositional Logic PL / 4. Soundness of PL
9543

The rules preserve validity from the axioms, so no thesis negates any other thesis

5. Theory of Logic / K. Features of Logics / 4. Completeness
9544

A system is 'weakly' complete if all wffs are derivable, and 'strongly' if theses are maximised
