Origin of the pronunciations of 観音 and 漢音

Question

The Japanese name for the deity Guanyin, 観音, seems as far as I can tell to be almost universally pronounced かんのん Kannon, and not かんおん Kan’on.

The origin of the name, as Wikipedia correctly gives it, is an Old or Middle Chinese translation of the Sanskrit name अवलोकितस्वर Avalokitásvara (later supplanted by अवलोकितेश्वर Avalokitéśvara) ‘he who looks down upon sound’.

The first of the two characters used in the Chinese translation, 觀 is pronounced guān /kʷan˥/ in modern Mandarin and is usually reconstructed as /kʷan/ or /kʷɑn/ in Middle Chinese. The Japanese pronunciation かん kan (earlier くゎん kwan) follows directly from this pronunciation.

The second character, 音 (yīn /(j)in˥/ in Mandarin), is reconstructed as something like /ʔiəm/ or /ʔjəm/ or /ʔi(ɪ)m/ in Middle Chinese. The Japanese Go’on pronunciation, おん on, follows fairly directly from this reconstruction, representing dialects where the /ə ~ ɪ/ was rounded and remained; while the Kan’on pronunciation, いん in, represents dialects where the initial /i ~ j/ merged with the nucleus, yielding /(j)i/. Whatever the precise form of the vowel, it definitely had a vocalic/glide initial.

Putting these two together, thus, should yield 観{かん}音{おん} kan’on, and it does seem to, rarely. Most commonly, though, it yields 観{かん}音{のん} kannon, as though 音 began with a nasal, which it obviously doesn’t.

Where does this extra nasal come from? Is it just simple 連声{れんじょう} in action?

And if so, then what about the historically almost entirely identical 漢音{かんおん}? The first character there, 漢 (Mandarin hàn /xan˦˩/) is reconstructed as Middle Chinese /xan ~ xαn/ or /han ~ hɑn/, with a non-labialised spirant rather than a labialised plosive as the initial, but with the same final (and the initials merged in Japanese anyway). So if 連声 hits 観音, it would be logical to expect it to also hit 漢音, or indeed 幹音{かんおん}, where the first character is reconstructed as /kan ~ kɑn/ and thus even closer to 観. Yet none of those seem to have gathered an extra nasal.

How random was 連声 when it was productive? How come it affected 観音, but not 漢音, if 連声 is indeed what lies behind the extra nasal in 観音?

Answer 1

I can only answer part of your question: the shift from かんおん to かんのん in the reading of 観音 is listed by several sources as due to 連声. (Shogakukan's 国語大辞典, and 大辞林 and 大辞泉)

The Japanese Wikipedia article on 観音 states:

日本語の「カンノン」は「観音」の呉音読みであり、連声によって「オン」が「ノン」になったものである。

The Japanese Wikipedia article on 連声 interestingly suggests that the 音読み of kanji could end in /t/, /m/, or /n/. Only /n/ persists in the modern language as an ending. The article also states (emphasis mine):

江戸時代以降になると、-t は独立の音節である「ツ」または「チ」にかわり、また -m および -n は撥音で発音されることが一般的になり、漢語の連声はほとんど見られなくなったが、一部の漢語には今も痕跡的に残っている。

The article lists a few other examples of 連声 following a first syllable ending in ん.

As to why 連声 occurs in 観音 but not 漢音, I cannot find anything specifically explaining why. To speculate, it might be a matter of deliberate differentiation. There's also the way that 音 in 漢音 as on is specifically about sound, and matches the on in other kanji-reading-related words like 呉音. Meanwhile, the 音 in 観音 is only etymologically about sound -- in terms of the modern term, Kannon is basically a name, and thus the sound element of 音 isn't as relevant.