Why are long vowels represented differently in hiragana and katakana?


[Wikiversity](http://en.wikibooks.org/wiki/Japanese/Pronunciation#Long_vowels)
says the following about long vowels in Japanese:

> A long vowel takes two morae. In rōmaji it's written with a macron: ā, ī, ū,
> ē and ō.
>
> In hiragana, it's written with an extra "あ" (a), "い" (i) or "う" (u)
> depending on the vowel. In katakana, it's marked by appending a dash-like
> symbol "ー".

Why are they represented differently in hiragana versus katakana?




Let's start by saying that not all words follow this rule. According to
[Japanese
Wikipedia](http://ja.wikipedia.org/wiki/%E9%95%B7%E9%9F%B3%E7%AC%A6), a number
of words are written in katakana but with doubled vowels, as if they were
written in hiragana (in which they can be equally well written):

> 例：シイタケ、フウトウカズラ、セイウチ、ホウセンカ、オオバコ

But these appear to be words that have kanjis, and fallen out of use. The
"dash" is used mainly for foreign and mimetic words:

> 例：ニャーン、テーブル

It would thus appear that the dash is mainly used in "new" words. I could
imagine as being a consequence of the use of new phonemes, such as `ティ` which
would look maybe weirder when elongated into `ティイ` than `ティー`.

As for the origin (I take this directly from the Japanese wikipedia), it is
said that it was invented to transcribe foreign languages, but it appears
(according to 国語学大辞典{こくごだいじてん}, literally "great dictionary of japanese
language") that it was first used by a scholar of the Edo period and that it
became commonplace in the Meiji era.

The symbol itself apparently originates from:

> 引く音の「引」の右側の旁（つくり）から取られたという説がある。

i.e. The right part of the kanji of `引{ひ}く`, "to pull", as in "to stretch the
sound". Note that this is a theory.

Apparently, in 1900, the ministry of education tried to enforce a new rule, by
which all long vowels (in kanji pronunciations and interjections) would be
denoted by a dash `-`, for example: 校長｛こーちょー｝ (principal of a school).
However, this ordinance was quickly repelled, in 1908.




What you've seen on Wikiversity is just a superficial explanation (or for
beginners?).

The spelling rule doesn't reside in _hiragana_ and _katakana_ , but in **words
often written in hiragana** (native and Sino-Japanese vocabulary) and **those
in katakana** (other loanwords and onomatopoeia). Mere rewriting hiragana ←→
katakana doesn't change the spelling.

The former way is mainly retained orthographically as reconfirmation of
traditional convention. The [original public
notice](http://www.mext.go.jp/b_menu/hakusho/nc/k19860701001/k19860701001.html)
on [modern orthography](https://en.wikipedia.org/wiki/Modern_kana_usage)
clearly differentiates between pronunciation notation (`ユー`) and real spelling
(`ゆう`).

`ー` appears in hiragana context indicating words or prolongation undefined in
the orthography.

> あーちゃん (a nickname), こんばんはー ("Eveniiiing!"), えー？ ("Gah!") cf. ええ ("Yes,
> sir/ma'am.")

While `アイウエオ` reduplication appears in katakana context representing syllable
or pitch breaking.

> アア溶岩 ("[ʻAʻā
> lava](https://en.wikipedia.org/wiki/Lava#.CA.BBA.CA.BB.C4.81)"), サナア
> ("Sana'a", Yemen's capital), オオオオオオ ("Arghhhhh!", maybe a dying scream)

