Call Me -Al

Some words have an -al on the end. Some don't. Some can do either. Here are those words.

Without -al With -al Mean the same?
analytic analytical not really
symbolic symbolical yes?
scientific scientifical yes; the latter exists but is obsolete
theoretic theoretical where both are acceptable, yes ("set-theoretic" vs "set-theoretical"), but the latter is more widely acceptable
geometric geometrical yes
acoustic acoustical uses of the latter are a subset of uses of the former

See also the superb answers to the question Why is it geometric but theoretical?