more from Rod Girle

Single Idea 7788

[catalogued under 4. Formal Logic / D. Modal Logic ML / 4. Alethic Modal Logic]

Full Idea

The four important logical equivalences in modal logic (the Modal Negation equivalences) are: ◊p↔□p, ◊p↔□p, □p↔◊p, and ◊p↔□p.

Gist of Idea

Modal logic has four basic modal negation equivalences


Rod Girle (Modal Logics and Philosophy [2000], 1.2)

Book Reference

Girle,Rod: 'Modal Logics and Philosophy' [Acumen 2000], p.3

A Reaction

[Possibly is written as a diamond, necessarily a square] These are parallel to a set of equivalences between quantifiers in predicate logic. They are called the four 'modal negation (MN) equivalences'.