
Originally Posted by
Ebizur
I think it does not need any explanation. Such a sound shift is both intuitively plausible and empirically common.
There is a comitative case marker in the Korean language (used to express meanings similar to English "(together/along) with" or "and") that actually exhibits morphophonemic variation, with one allomorph (/-wa/) occurring after any stem that ends in a vowel and another allomorph (/-gwa/) occurring after any stem that ends in a consonant. (In Late Middle Korean, the /-gwa/ variant would merge with the final /-h/ of a stem to produce /kwa/, but postvocalic /h/ has been eliminated in the meantime. Modern Korean has regularized the paradigm, so it has /nara-wa/ "[the] country and ~, (along) with [the] country" where Late Middle Korean had narakwa.)
Anyway, neither */gwa/ > /wa/ nor */wa/ > /gwa/ is a particularly unusual sound change.