more from C.I. Lewis

Single Idea 7803

[catalogued under 10. Modality / B. Possibility / 8. Conditionals / a. Conditionals]

Full Idea

C.I.Lewis began his groundbreaking work in modal logic because he was concerned about the unreliability of the material conditional as a translation of 'If ... then' conditionals.


p materially implies q if not(p-is-true and q-is-false)

Gist of Idea

Modal logic began with translation difficulties for 'If...then'


report of C.I. Lewis (Symbolic Logic (with Langford) [1932]) by Rod Girle - Modal Logics and Philosophy 12.3

Book Reference

Girle,Rod: 'Modal Logics and Philosophy' [Acumen 2000], p.180

A Reaction

Compare 'if this is square then it has four corners' with 'if it rains then our afternoon is ruined'. Different modalities seem to be involved. We even find that 'a square has four corners' will be materially implied if it rains!