Why are the particles "は" (ha⇒wa), "へ" (he⇒e), and "を" (wo⇒o) not spelled phonetically?


As far as I know only three words (or particles) have irregular, non-phonetic
spelling in Japanese:

  * "は" - The topic particle is pronounced "wa" but the kana is otherwise pronounced "ha"
  * "へ" - The movement towards particle is pronounced "e" but the kana is otherwise pronounced "h"
  * "を" - The kana is only used for the object particle as far as I know and in the kana table takes the position of "wo" but pronunciation seems to hover somewhere between "o" and "wo"

So did the sounds of these particles change since the spelling was set down?
Or were the spellings intentionally chosen for some reason? Are there any
other irregular kana spellings I omitted?

(P.S. I found the question [Why is は pronounced as わ when used as a topic
particle?](https://japanese.stackexchange.com/questions/348/why-is-pronounced-
as-when-used-as-a-topic-particle) while working on this question but since
mine is broader I decided to go ahead anyway, plus it might give an
opportunity to test our duplicate marking strategies here)

**EDIT**

Some of the comments to Lukman's answer below suggests that these might not
seem like irregular sounds or kana to native speakers. I was surprised that
people interpreted this question to be about romaji rather than being about
kana and particles as I intended it.

So a further question: Are these particles and their kana and pronunciations
seen as irregular by native Japanese speakers? Or just to learners of
Japanese? And what do Japanese and non-Japanese linguists think?




I'll give you the same one I gave to the other question: Yes, the sounds of
these words has changed since their spelling was set down. In general, no
matter the language, whenever you see a discrepancy between spelling and
pronunciation that is not entirely regular, this is the result of sound
changes. And while there are some counter-examples of words that have changed
their spelling to something that doesn't reflect any prior pronunciation due
to [folk etymology](http://en.wikipedia.org/wiki/Folk_etymology) (such as the
English word `island`, which was thought to come from the Latin `insula` so a
totally superfluous `s` was inserted there) , they are rather rare.

In the case of the unruly Japanese particles を, は and へ, they all reflect an
earlier pronunciation that was retained in spelling for many words in
[historical kana usage](http://en.wikipedia.org/wiki/Historical_kana_usage),
but after the major language reforms of 1946, this conservative spelling was
kept only for these 3 particles.

To see what happened here exactly, we first have to get acquainted with
traditional kana, that had two extra letters (ゑ and ゐ in hiragana). These
letters are usually transliterated as WE and WI respectively, and that was
indeed their pronunciation in Old and probably Classical Japanese. In the
early 20th century however, the entire W-column (ワ行) has merged with the
vowel-column (ア行), except for the letter わ itself. As for the H-column (ハ行),
it merged even earlier with the ワ行 in some positions (between vowels), as I've
explained in [my other
answer](https://japanese.stackexchange.com/questions/348/why-is-pronounced-as-
when-used-as-a-topic-particle). Since the ハ行 was already merged with the ワ行
for these positions, it also underwent the merger with the ア行 when it came. So
to lay it out more clearly, this is the order of the changes:

  1. /p/ softens to /f/ and becomes /w/ between vowels. 
    1. は (originally pronounced as PA) is now pronounced WA. 
    2. へ (originally pronounced as PE) is now pronounced WE. 
  2. /w/ disappears before all vowels except /a/. 
    1. は (previously pronounced as WA) remains WA. 
    2. へ (previously pronounced as WE) becomes E. 
    3. を、ゑ、ゐ (originally pronounced as WO, WE, WI) become O, E, I.  

Up to 1946, you could find, for instance, spellings such as アヲイ (for 青い, the
color blue) and アヲヒ (a name for a family of flowers, sometimes translated as
Hollyhock). `awoi` underwent the disapperance of `w` and became `aoi`, while
`awopi` became first `awowi` and then `aoi`.




I'll give you the same one I gave to the other question: Yes, the sounds of
these words has changed since their spelling was set down. In general, no
matter the language, whenever you see a discrepancy between spelling and
pronunciation that is not entirely regular, this is the result of sound
changes. And while there are some counter-examples of words that have changed
their spelling to something that doesn't reflect any prior pronunciation due
to [folk etymology](http://en.wikipedia.org/wiki/Folk_etymology) (such as the
English word `island`, which was thought to come from the Latin `insula` so a
totally superfluous `s` was inserted there) , they are rather rare.

In the case of the unruly Japanese particles を, は and へ, they all reflect an
earlier pronunciation that was retained in spelling for many words in
[historical kana usage](http://en.wikipedia.org/wiki/Historical_kana_usage),
but after the major language reforms of 1946, this conservative spelling was
kept only for these 3 particles.

To see what happened here exactly, we first have to get acquainted with
traditional kana, that had two extra letters (ゑ and ゐ in hiragana). These
letters are usually transliterated as WE and WI respectively, and that was
indeed their pronunciation in Old and probably Classical Japanese. In the
early 20th century however, the entire W-column (ワ行) has merged with the
vowel-column (ア行), except for the letter わ itself. As for the H-column (ハ行),
it merged even earlier with the ワ行 in some positions (between vowels), as I've
explained in [my other
answer](https://japanese.stackexchange.com/questions/348/why-is-pronounced-as-
when-used-as-a-topic-particle). Since the ハ行 was already merged with the ワ行
for these positions, it also underwent the merger with the ア行 when it came. So
to lay it out more clearly, this is the order of the changes:

  1. /p/ softens to /f/ and becomes /w/ between vowels. 
    1. は (originally pronounced as PA) is now pronounced WA. 
    2. へ (originally pronounced as PE) is now pronounced WE. 
  2. /w/ disappears before all vowels except /a/. 
    1. は (previously pronounced as WA) remains WA. 
    2. へ (previously pronounced as WE) becomes E. 
    3. を、ゑ、ゐ (originally pronounced as WO, WE, WI) become O, E, I.  

Up to 1946, you could find, for instance, spellings such as アヲイ (for 青い, the
color blue) and アヲヒ (a name for a family of flowers, sometimes translated as
Hollyhock). `awoi` underwent the disapperance of `w` and became `aoi`, while
`awopi` became first `awowi` and then `aoi`.

