The yomikata of 十三


This has been obsessing me for quite a while. While 十三 is normally pronounced
ジュウサン, it is often pronounced ジュウゾウ in people's names and also pronounced
ジュウソウ in names of places. I am wondering how these pronunciations come into
place. Are there any relevant historical perspectives? I don't see exotic
alternative pronunciations for say 12 and 14, and it is not the pronunciation
of traditional Japanese numbers either (which seems to be トサ), so what is
making 13 so special?




### Odd readings of 三: looking back in the history

I've read here and there that researchers think that the Chinese-derived
reading さん was originally borrowed as さむ. This is based partly on the
reconstructed Middle Chinese reading of `/sɑm/`, and partly on the fact that
Old Japanese (the stage of the language when most kanji were borrowed) didn't
have any ん yet. In fact, the kana ん comes from a
[hentaigana](https://en.wikipedia.org/wiki/Hentaigana) form of む, deriving
from kanji 无.

However, む on the end has been unstable historically, and tends to evolve
phonologically in a few different ways.

  * It becomes ん, as in archaic / formal constructions like 言わ[ん]【●】とする, from 言わ[む]【●】とする, where 言わむ is the classical volitional.
  * It becomes う, as in 言わ[う]【●】, the precursor to modern volitional 言おう. 
  * In rarer cases, the `/m/` in む shifted to a `/b/` sound to become ぶ -- and we see that `/m/` ↔ `/b/` alternation in a number of words and placenames, like さびしい ↔ さみしい, or the name of the "Tama River" in Tokyo, which seems to become "Taba" at some points along its course.

### Consonant shifts

Looking again at 三, the ancient さ[む]【●】 reading shifted regularly to さ[ん]【●】
in most instances -- but that final む took the other routes and became ぶ or う
in a few places, notably in names.

For instance, there's the not-uncommon male given name さ[ぶ]【●】ろう, spelled in
kanji as 三郎. We would ordinarily expect this to be さ[ん]【●】ろう instead, but
here, ancient さ[む]【●】 became さ[ぶ]【●】, giving us the modern さぶろう reading.

In your example, 十三 would ordinarily be じゅうさ[ん]【●】, as you note. However, in
some names, the ancient さ[む]【●】 became さ[う]【●】 instead. That would give us
じゅうさう, to which we add [rendaku](https://en.wikipedia.org/wiki/Rendaku), the
voicing of an initial consonant in compounds, to yield じゅう[ざ]【●】う.

But what about the vowels?

### Vowel shifts

Through normal vowel shifts, many cases of `/au/` in older forms of Japanese
(pronounced like _ow!_ in English) monophthongized or flattened out to became
`/ɔː/` (pronounced like _awwww_ in English).

This `/ɔː/` vowel sound, not-quite-あ-not-quite-お, was still distinct four
hundred years ago, which we can see in various entries in the 1603 Portuguese-
Japanese dictionary, [_Vocabulario da Lingoa de Iapam_ , a.k.a. the
日葡【にっぽ】辞書【じしょ】](https://books.google.com/books?id=TFJAAQAAMAAJ&pg=PP133#v=thumbnail&q=coxocuna&f=false).
Click through to the link, expand the page, and look at the two entries above
the yellow-highlighted one -- **Còxocu** for 紅色 ("Curenaino iro", i.e. 紅の色),
and **Cǒxocu** for 好色 ("Irogonomi", i.e. 色好み). Regular お is just plain **o**
in the dictionary. Long おお or おう is **ò**. And the oddball **ǒ** is used to
indicate that `/ɔː/` sound that arose from the flattening of `/au/`. And sure
enough, we can see in many monolingual Japanese dictionaries that 紅色 has
always been spelled in kana as [こ]【●】[う]【●】しょく, aligning with the **ò** in the
_Nippo Jisho_ , while 好色 _used to be_ spelled in kana as [か]【●】[う]【●】しょく,
pointing towards `/ɔː/` and aligning with the **ǒ** in the _Nippo Jisho_.
These old kana spellings were made obsolete by spelling reforms in the early-
to-mid 20th century, when there was a push to get the then-archaic spelling
conventions to align more closely with everyday pronunciation.

So between 1603 and today, all of those `/ɔː/` sounds further shifted to
become the long `/oː/` sounds we're used to in modern Japanese, producing the
long `/oː/` sound we hear in じゅうぞう.




### Odd readings of 三: looking back in the history

I've read here and there that researchers think that the Chinese-derived
reading さん was originally borrowed as さむ. This is based partly on the
reconstructed Middle Chinese reading of `/sɑm/`, and partly on the fact that
Old Japanese (the stage of the language when most kanji were borrowed) didn't
have any ん yet. In fact, the kana ん comes from a
[hentaigana](https://en.wikipedia.org/wiki/Hentaigana) form of む, deriving
from kanji 无.

However, む on the end has been unstable historically, and tends to evolve
phonologically in a few different ways.

  * It becomes ん, as in archaic / formal constructions like 言わ[ん]【●】とする, from 言わ[む]【●】とする, where 言わむ is the classical volitional.
  * It becomes う, as in 言わ[う]【●】, the precursor to modern volitional 言おう. 
  * In rarer cases, the `/m/` in む shifted to a `/b/` sound to become ぶ -- and we see that `/m/` ↔ `/b/` alternation in a number of words and placenames, like さびしい ↔ さみしい, or the name of the "Tama River" in Tokyo, which seems to become "Taba" at some points along its course.

### Consonant shifts

Looking again at 三, the ancient さ[む]【●】 reading shifted regularly to さ[ん]【●】
in most instances -- but that final む took the other routes and became ぶ or う
in a few places, notably in names.

For instance, there's the not-uncommon male given name さ[ぶ]【●】ろう, spelled in
kanji as 三郎. We would ordinarily expect this to be さ[ん]【●】ろう instead, but
here, ancient さ[む]【●】 became さ[ぶ]【●】, giving us the modern さぶろう reading.

In your example, 十三 would ordinarily be じゅうさ[ん]【●】, as you note. However, in
some names, the ancient さ[む]【●】 became さ[う]【●】 instead. That would give us
じゅうさう, to which we add [rendaku](https://en.wikipedia.org/wiki/Rendaku), the
voicing of an initial consonant in compounds, to yield じゅう[ざ]【●】う.

But what about the vowels?

### Vowel shifts

Through normal vowel shifts, many cases of `/au/` in older forms of Japanese
(pronounced like _ow!_ in English) monophthongized or flattened out to became
`/ɔː/` (pronounced like _awwww_ in English).

This `/ɔː/` vowel sound, not-quite-あ-not-quite-お, was still distinct four
hundred years ago, which we can see in various entries in the 1603 Portuguese-
Japanese dictionary, [_Vocabulario da Lingoa de Iapam_ , a.k.a. the
日葡【にっぽ】辞書【じしょ】](https://books.google.com/books?id=TFJAAQAAMAAJ&pg=PP133#v=thumbnail&q=coxocuna&f=false).
Click through to the link, expand the page, and look at the two entries above
the yellow-highlighted one -- **Còxocu** for 紅色 ("Curenaino iro", i.e. 紅の色),
and **Cǒxocu** for 好色 ("Irogonomi", i.e. 色好み). Regular お is just plain **o**
in the dictionary. Long おお or おう is **ò**. And the oddball **ǒ** is used to
indicate that `/ɔː/` sound that arose from the flattening of `/au/`. And sure
enough, we can see in many monolingual Japanese dictionaries that 紅色 has
always been spelled in kana as [こ]【●】[う]【●】しょく, aligning with the **ò** in the
_Nippo Jisho_ , while 好色 _used to be_ spelled in kana as [か]【●】[う]【●】しょく,
pointing towards `/ɔː/` and aligning with the **ǒ** in the _Nippo Jisho_.
These old kana spellings were made obsolete by spelling reforms in the early-
to-mid 20th century, when there was a push to get the then-archaic spelling
conventions to align more closely with everyday pronunciation.

So between 1603 and today, all of those `/ɔː/` sounds further shifted to
become the long `/oː/` sounds we're used to in modern Japanese, producing the
long `/oː/` sound we hear in じゅうぞう.

