When/why would one write a word using 直音表記?


I looked up [釈迦 at
goo辞書](http://dictionary.goo.ne.jp/srch/jn/%E9%87%88%E8%BF%A6/m0u/) and
noticed that there were two alternate readings presented for this word:
[さか](http://dictionary.goo.ne.jp/leaf/jn2/86197/m0u/%E9%87%88%E8%BF%A6/) and
[しゃか](http://dictionary.goo.ne.jp/leaf/jn2/101493/m0u/%E9%87%88%E8%BF%A6/).
The さか reading is given as being 『「しゃか」の直音表記。』, so these two are clearly the
same lexical item, just with different kana representations.

I then looked up [直音](http://ja.wikipedia.org/wiki/%E7%9B%B4%E9%9F%B3) and
found that this term basically refers to any mora that can be written using a
single kana - so it includes あ・き・す・て・の but excludes きゃ・しゅ・ちょ, as well as non-
standard two-kana morae like グァ. One can respell
[拗音](http://ja.wikipedia.org/wiki/%E6%8B%97%E9%9F%B3) (i.e. non-直音) as 直音 by
"removing" the middle phone, e.g. /sha/ → /sa/, /myu/ → /mu/, etc.

So I understand what 直音 are, but I do not know why one would choose to take a
perfectly good word like しゃか and then rewrite it using only 直音 so that you get
さか. When, historically, did people prefer 直音表記 and why? Are there some types
of words where the use of 直音表記 is particularly common, e.g. Buddhist
terminology?




Historically there were multiple way to write a word, and this wasn't
standardized. For example, some very old documents contain both 直音表記 and ヤ行表記.

This was subsequently standardized as
[歴史的仮名遣い](http://ja.wikipedia.org/wiki/%E6%AD%B4%E5%8F%B2%E7%9A%84%E4%BB%AE%E5%90%8D%E9%81%A3)
and then
[現代仮名遣い](http://ja.wikipedia.org/wiki/%E7%8F%BE%E4%BB%A3%E4%BB%AE%E5%90%8D%E9%81%A3%E3%81%84).

So, unless you are living in an ancient era you wouldn't use 直音表記.

