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?

related: https://www.quora.com/Are-the-Hais-in-Japanese-and-Cantonese-related

  • 3
    Personally I don't believe so. Japanese underwent sound change of [p] > [h] over the past and "hai" could be "pai" in Old Japanese, while in Cantonese, the sound change was [k] > [h] and the early pronunciation of 係 was something like /kei/. Of course this does not rule the possibility that the two words were somehow related but only written in its modern form later...
    – user58955
    Commented Dec 17, 2014 at 1:50
  • 2
    It's interesting. I've tried to do some search, it seems just a popular belief, not admitted by academic community. Reference:はい
    – user4072
    Commented Dec 17, 2014 at 2:38

2 Answers 2


The Japanese wiki page mentions that the claim is a "folk theory" that is "denied by academics".

An alternative etymology for Cantonese hai6 comes from 系/繫. I don't have this book, but apparently Jerry Norman suggests this in Chinese (1988). This word had a very early meaning of 'to be connected', was used as a copula in later texts, and the phonological evidence is certainly not lacking.

To summarize the wiki article, はい is thought to come from either 拝, a courteously used Sino-Japanese word, or a corruption of similar words such as "ai" and "ei". It is only attested from the Edo period onwards, which is very recent.

Considering the relative isolation of Japan in the past few centuries, the word would have had to travel from Japan into rural Chinese villages in the past 100 years or so. Even if this did happen, it would likely have been heavily documented by various sources. The Chinese-internal etymology is much simpler and I personally see no reason to believe the Japanese etymology without further evidence.

  • 1
    The statement on that wiki article that the 係 theory is denied by academics has no sources either.
    – user102008
    Commented Dec 19, 2014 at 2:03

Definitely a false cognate. You would think that such basic words as yes and no are native rather than foreign loan words.

はい has thus always basically been written in some form of kana, and when Chinese characters have been used exclusively, it may have been rendered phonetically with such a character. For various reasons, 係 is not a good classical candidate.

  • 1
    I am not sure I understand what you mean by "when Chinese characters have been used exclusively, it may have been rendered phonetically with such a character". As far as I know, 係 is a recent Written Cantonese borrowing of a character to phonetically represent a Cantonese word which had no representation in standard Chinese.
    – user102008
    Commented Dec 17, 2014 at 23:57
  • I believe @倪阔乐 means the period of Japanese history when Chinese characters were exclusively used in Japan, i.e. before hiragana was invented or mainstream.
    – Ming
    Commented Dec 18, 2014 at 2:09

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