My prof taught us to use trees to prove modal logic arguments. Trees seem to provide a more efficient way to test arguments than Fitch does. However, I find that trees generally, and alethic (modal) trees especially, don't read as elegantly as the methods that resemble Fitch. Can Fitch, or a system that resembles it, accommodate any of the modal logics (i.e. Alethic, temporal, deontic, etc.)? If so, is there a resource that explains how to use the system to prove modal logic arguments?

Thank you,



1 Answer 1


There are Fitch systems for about twenty different modal logics described very briskly here


More than enough to be going on with, I guess!

More expansively, Garson's good and accessible book Modal Logic for Philosophers (CUP) introduces Fitch style systems for modal logics.


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