I've just learned that Lao has two words for "to be", that are mostly interchangeable:
They both begin with a labial, have an "e-like" vowel, and end "n".
I think it's pretty established that the "b", "m", and "p" sounds can be variants of each other in variants of the same word or in closely related words.
The vowel in
ເປັນ is an
/e/ but as fpr the vowel in
ແມ່ນ I'm not sure if it's more like
/ɛ/, but I also believe that both of these can have close relationships with an
/e/ sound in a language.
The Isan language, generally considered a dialect of Lao spoken in Thailand with a different set of recent influences and now written in the Thai script, also has the two copulae:
There are two copulas used in Isan, as in Lao, one for things relating to people,
/pen/), and one for objects and animals,
I'm wondering if these two words that are similar in sound and similar in function are etymologically variants. I don't think Thai has two words and Zhuang seems to have an unrelated word as its copula: