Combining Texts

Ideas for 'Against Coherence', 'W.V. Quine' and 'Tractatus de corpore Christi'

unexpand these ideas     |    start again     |     choose another area for these texts

display all the ideas for this combination of texts

---

1 idea

4. Formal Logic / D. Modal Logic ML / 4. Alethic Modal Logic

8480	S4: 'poss that poss that p' implies 'poss that p'; S5: 'poss that nec that p' implies 'nec that p' [Orenstein]
	Full Idea: The five systems of propositional modal logic contain successively stronger conceptions of necessity. In S4 'it is poss that it is poss that p' implies 'it is poss that p'. In S5, 'it is poss that it is nec that p' implies 'it is nec that p'.
	From: Alex Orenstein (W.V. Quine [2002], Ch.7)
	A reaction: C.I. Lewis originated this stuff. Any serious student of modality is probably going to have to pick a system. E.g. Nathan Salmon says that the correct modal logic is even weaker than S4.