The Cantonese word meaning "to be", written as 係 (Jyutping: hai6) sounds similar to the Japanese word はい ("hai" in various Romanizations). Both words are used to answer "yes" or "it is correct" to yes-no questions.
The Japanese Wikipedia article on Cantonese contains a sentence I find interesting:
I think the second part of that says that there is a theory that 係 in Cantonese is the source of the はい in Japanese. However, the article does not provide any sources for this statement.
My questions are:
- Is this theory documented anywhere? And what are the details of this theory?
- Is this theory plausible?
- What is the source of the Cantonese word 係 (meaning "to be", ignoring the other meanings of that character) in Middle Chinese?
- What is the source of the Japanese word はい?
- Is it possible that they share a common source?