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What’s a good introduction to Modal Logic?(r/philosophy)
Propositional logics and modal logics are quite different, and thus I could really use more info on what exactly you’re looking for.
I would also suggest taking an actual course in logic before attempting to teach yourself anything, especially modal logic.
The Logic Book is my favourite intro to logic textbook. It covers all of first-order classical logic in a thorough yet easy way. However it’s not particularly cheap.
As for modal logic, I used First-Order Modal Logic by Fitting and Mendelsohn, however it’s fairly difficult and uses an atrocious axiomatic proof system instead of natural deduction. Luckily it also contains tableaux, however a natural deduction system would have been preferable.
I have heard Garson’s Modal Logic for Philosophers suggested quite often, however I haven’t used it personally.
I want to stress that unless you have taken a course in propositional and first-order logics, you will get little to nothing out of the modal textbooks, and likely will not be able to work correctly through any standard classical textbook alone. This isn’t meant to dissuade you, but rather to motivate you to take a course in logic.