Meaning/Use of 陰陽 in Japanese and differences in reading (Onmyō/In'yō)


I'd like to know if the word 陰陽 is commonly used to describe Yin and Yang as a
"series of words", or if it's (only) used to describe the combination of Yin
and Yang as one single term, so to speak. Basically, would it mean "'Yin' and
'Yang'" or "Yin and Yang", or perhaps both? I'm aware that the original
concept is Chinese, but it also exists in Japanese as 陰陽道, no? What I
basically would like to know is if saying 陰陽 is different from saying 陰と陽.

Also, the word can be read as Onmyō and In'yō, but is there any different in
the reading's meaning? I'm aware that the reading of a kanji normally doesn't
change its meaning, but it often gives more information, right? For example, 弟
with the reading ボブ to denote that the younger brother that is meant is Bob
and not Jim. Is that the case here?




It might be the difference between **Go-on** (呉音, "sound from the Wu region")
and **Kan-on** (漢音, "Han sound").

According to [this](https://en.wikipedia.org/wiki/Go-on), Go-on is:

> introduced to Japan during the 5th and 6th centuries, when China was divided
> into separate Northern and Southern dynasties, go-on readings are possibly
> imported either directly from the Southern dynasty or the Korean Peninsula.
> This explanation is based mainly on historical reasoning: there was an
> influx of thinkers from China and Korea to Japan at that time, including
> both Buddhist and Confucian practitioners. However, there is no historical
> documentation to conclusively demonstrate that go-on readings are actually
> based on southern Chinese.

According to [this](https://en.wikipedia.org/wiki/Kan-on), Kan-on is:

> one of the sources of pronunciation of Japanese kanji. They were borrowed
> during the Tang dynasty (7th to 9th century), introduced by, among others,
> envoys from Japanese missions to Tang China. This period corresponds with
> the Japanese Nara period.
>
> Kan-on is based on the central Chang'an pronunciation. The name Kan could
> refer to the Han dynasty, which also had Chang'an as its capital
> city.Furthermore, Kan has also become a description for all things Chinese,
> e.g., Kanji ('Chinese characters').
>
> Kan'on partly **displaced the earlier go'on** , which were "just imitations
> of Korean imitations, but Kan-on were imitations of the real things."

Apart from the explanation of Kan-on above,
[here](https://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q1416422854)
is an article that the Japanese government at that time often **abolished Go-
on and designated Kan-on as formal pronunciation of _kanji_**. As a result of
the policy of the government, we have a lot of Kan-on as _on-yomi_ for _kanji_
like [陰陽]{in-yoh}, but Go-on remains a little as _on-yomi_ for _kanji_ like
[陰陽]{on-myoh} in certain field.  
I quote the whole article in Japanese as follows.

> **陰陽師の読み方って、『おんみょうじ』以外に『いんようし』とも読めるのですか？**
>
>
> 「いん」は漢音（七～八世紀ごろに遣唐使が伝えた中国語音）、「おん（おむ）」は呉音（六世紀ごろ、またはそれ以前におもに仏典を通じて伝わった中国語音）です。「陰」を「おん」と読む例は、仏教の「四苦八苦」の中に、「五陰盛苦（ごおんじょうく）」というのがあります。漢字音については、たびたび、「漢音を正音とし、呉音を廃する」旨のお触れがでました。そういう影響で、現代にいたるまで、漢字音の大半は漢音です。ただし、古くから伝わって、もうそれが漢語だと意識しないぐらい日本語になじんでしまった言葉は、あまり改まりませんでした。「おんみょうじ」もその一つだと思います。ことさらに漢音で「いんようし」と発音する人も時にはいたのかもしれません。それなら、「いんようし」でも正しいということになりますね。

