Onbin

Onbin is a set of sound changes that occurred in Early Middle Japanese around the end of the eighth century to the beginning of the tenth century, first attested in written texts of the Heian period. Onbin changes affected certain consonant-vowel sequences in non-word-initial position, causing them to become replaced with either a single vowel sound or a single consonant sound. Onbin played a role in diversifying the syllable structure of native Japanese words by creating heavy syllables that ended in two vowels or in a vowel followed by a consonant.
Historical onbin changes did not occur systematically, and some sequences could yield multiple outcomes. The non-deterministic nature of the historical sound changes is exemplified by doublets showing different outcomes of the same original form, such as komichi versus kōji from original, or akindo versus akyūdo from original. However, some onbin changes have come to be grammaticalized in the conjugation of Japanese verbs: as a result, certain verbs systematically display an "onbin stem" before certain suffixes in standard modern Japanese. The formation of these onbin stems varies between dialects.

Sound changes

The outcomes of onbin changes were bound moraic phonemes pronounced in the same syllable as the preceding vowel. Four distinct outcomes can be identified based on modern Japanese kana spellings: the two high vowels and the two moraic consonants :

, currently spelled as い in hiragana and イ in katakana
, currently spelled as う in hiragana and ウ in katakana
or N-onbin, currently spelled as ん in hiragana and ン in katakana
or Q-onbin, currently spelled as っ in hiragana and ッ in katakana

divides i-onbin and u-onbin into two categories based on whether they were originally nasalized, and so recognizes six possible outcomes of onbin in the Early Middle Japanese period:.
The core set of onbin changes affected non-word-initial syllables that contained the consonants followed by. Some onbin changes could affect word-final syllables, such as the change of to or to , and occasionally to, or to or . In contrast, onbin changes involving seem to be attested only in the middle of words.
These core changes can be summarized as follows:
Subscript numbers distinguish syllables that were different in Old Japanese, as indicated by man'yōgana, but that merged in the transition to Early Middle Japanese. considers it likely that onbin changes affected only and not , whereas disagrees. Since syllables with /i₂/ were less frequent, the relevant evidence is limited, and there is a possible case of > in the word, normally derived from Old Japanese tuki₂ "moon, month": Frellesvig argues this could be a folk etymology.

Additional changes

When the consonant in the affected sequence was either nasal or prenasalized, onbin produced a nasal output: either a nasalized high vowel or a moraic nasal consonant. These nasal sounds caused following to be replaced with their prenasalized counterparts,. By Late Middle Japanese, the nasalized vowels had merged with, and the change of to after a nasal sound ceased to apply as an automatic process, although it had lasting effects on the form of some inflectional morphemes and lexicalized compound words.
During Late Middle Japanese, vowel sequences ending in fused into long vowels. If the first vowel was originally or, the resulting long vowel was preceded by a palatal glide. This produced the following outcomes:

late Early Middle Japanese	Late Middle Japanese	Modern Japanese

Because of this vowel fusion, words with u-onbin, such as, do not always contain the vowel phoneme in modern Japanese, although they are still spelled with the kana う/ウ because of a convention of spelling long non-phonetically in this context.

In verbs and adjectives

Verb stems

As a result of onbin changes, consonant-stem verbs developed variant "onbin stems" used before certain suffixes. Consonant-stem verbs are those that can be analyzed as having underlying stems that end in a consonant : these verbs take the suffix -u in the dictionary form, in contrast to vowel-stem verbs, which have stems that end in either or and take the suffix -ru in the dictionary form. In Japanese grammatical terminology, consonant-stem verbs are called five-grade verbs, because their inflected forms make use of the five kana that represent the stem-final consonant plus each of the five Japanese vowels. Verbs with stems ending in show an additional complication: stem-final is deleted before suffixes that start with, since Japanese phonotactics only allow to occur before the vowel. In terms of historical development, verb stems that end in originally ended in the consonant *p.
The onbin stem developed from the Early Middle Japanese infinitive form, which ended in. When the infinitive form of a consonant-stem verb ended in one of the syllables, it could undergo the [|onbin sound changes described above]. In addition, it came to be possible for to undergo analogous changes in this context: thus, could become and could become . argues that verbs with stems ending in developed onbin stems purely as a result of the morphological process of analogy, rather than as a result of the same phonetic processes as the other onbin changes.
In modern Standard Japanese, the form of a verb's onbin stem can typically be predicted from the underlying stem-final consonant: give, give , gives, and gives . Verbs with underlying stems ending in do not show onbin in contemporary standard speech, but instead use before the relevant suffixes.
A few verbs have an exceptionally formed onbin stem. For example:

the verb has an onbin stem in, e.g., rather than the expected.
the verbs and have u-onbin stems, e.g.,, rather than the expected.
the honorific verbs,,,, and all exhibit an i-onbin stem prior to the polite auxiliary verb, e.g.,, etc., rather than the expected non-onbin form. These verbs have the expected onbin forms before suffixes -ta, -te, -tara, -tari.

Dialects show some differences in the formation of onbin stems. Some dialects regularly use u-onbin for verb with underlying stems that end in or verbs with underlying stems that end in .

Use of u-onbin for verbs with stems that end in is a feature of dialects spoken in western regions, such as Kansai and Kyushu. For example, in the Kyoto dialect the verb has the past form kōta, in contrast to standard Japanese katta. The 17th-century Arte da Lingoa de Iapam by João Rodrigues identified the use of u-onbin in this context as a feature of the Japanese spoken in Kyoto, in contrast to the use of Q in the Kanto dialect.
Use of u-onbin for verbs with stems that end in is found on Kyushu and in the far west of Honshu; in contrast, in Kyoto and most of Kansai, these verbs currently show consonantal onbin as in the standard language. For example, in some dialects the verb has the gerund form yōde, in contrast to yonde. The voicing of the suffix -te to -de indicates that these u-onbin forms originally contained nasalized.
Use of i-onbin for verbs with stems that end in survives dialectally in some regions, including much of Kansai. Thus, forms such as daite can occur in place of standard dashite for the gerund of the verb .
Some dialect forms show consonantal onbin in verbs with stems ending in or, where standard Japanese has i-onbin.

The use of onbin stems in inflected verb forms never become normative in literary written Classical Japanese. It is difficult to tell how frequent they were in speech at various historical periods.
, citing, gives the following chronology for the written attestation of onbin in verb forms:

to : seen from the late 9th century.
to : rarely seen until the mid 10th century, from which point it is found regularly.
to : seen from the first half of the 11th century.
to : seen sporadically from 11th century, becoming regular at the end of the 16th century.

However, suggests that onbin changes must have been active well before these dates, arguing that they precede [|the intervocalic merger] of and and most likely began in the early 9th century or even the late 8th century.

Adjective endings

Two suffixes used in the inflection of adjectives underwent onbin changes. The Old Japanese adnominal ending -ki developed by onbin into the Late Middle Japanese and Modern Japanese nonpast ending -i, as in takai, the nonpast form of the adjective stem. The adjectival infinitive ending -ku developed an onbin variant -u: however, -ku remains the normal form of this ending in Standard Japanese. The use of -u as an adjectival infinitive ending is a characteristic of the language spoken in the Kansai and Kyushu regions. Using the adjective taka- again as an example, the Kansai dialect form takō corresponds to the Standard Japanese infinitive takaku. The pronunciation of the adjectival infinitive ending as -u in Kyoto vs. -ku in the Kanto region is mentioned as a dialectal difference in Rodrigues' Arte da Lingoa de Iapam. The variant ending -u shows some limited use in Standard Japanese as part of the rarely used "super-polite" construction and in a few isolated, fixed expressions: its use in these contexts can be attributed to borrowing from the Kyoto dialect.

Phonetic development

Onbin sound changes likely had their roots in earlier phonetic variation in the pronunciation of Old Japanese consonants and vowels. Namely, the Old Japanese consonants might have varied phonetically between voiceless stops, voiced stops, voiceless fricatives, and voiced continuants. The consonants were prenasalized and possibly could vary between stops and continuants ; vowels before were likely phonetically nasalized. The high vowels could possibly be reduced to coarticulations on the preceding consonant.
Between vowels in the middle of a word, original merged with the phoneme around the second half of the tenth century or during the 11th century. After this merger, eventually was lost before any vowel other than. At the start of a word, original had come to be regularly pronounced as a voiceless labial fricative by the end of the 16th century. It was once widely thought that was completely replaced with already in Old Japanese, but argues that this assumption is not well justified. According to the traditional assumption, intervocalic merged with as a result of being voiced to. According to a competing hypothesis, word-medial intervocalic was already phonetically voiced or in Early Middle Japanese prior to its merger with.
Consonantal variants of verbal onbin stems are attested later than the vocalic variants, but this does not necessarily mean that consonantal onbin are chronologically more recent sound changes: it could simply mean that the varieties of speech in which they arose were not well represented in writing until later on.
There is disagreement about the exact phonetic path by which onbin developed. The development of the consonantal onbin N and Q can be explained in terms of vowel deletion, whereas the development of i- and u-onbin can be interpreted as involving deletion of consonants between vowels. If intervocalic consonant deletion is the correct explanation for the origin of u-onbin from sequences involving original labial consonants, then the deletion of these consonants must have been preceded by a sound change that turned into in contexts where onbin would occur. Such a change does appear to be attested by spelling variations in texts from the 11th and 12th centuries, although some of this evidence admits other interpretations. The hypothesis of intervocalic consonant deletion implies that in cases where i-onbin or u-onbin is derived from a consonant-vowel sequence that originally started with a nasal or prenasalized consonant, the change of following to prenasalized was not caused by assimilation between adjacent consonants; rather, it may have arisen by 'rightward' spreading of nasality from a phonetically nasalized vowel that originally preceded the deleted consonant. The following examples illustrate ways i- and u-onbin might have developed per this approach:

De Chene 1991 advocates an alternative account for the development of i-onbin from original and u-onbin from original, arguing there was an initial change of to moraic, to moraic, and to moraic, followed by vocalization of moraic to and of moraic and to . In support, de Chene cites the development of from original in the form kauburu "to place on the head' from kagapuru, arguing that this is easier to explain in terms of moraic nasal formation and vocalization rather than intervocalic consonant loss. De Chene also argues that the lack of onbin outcomes for word-final and implies that the development of these sequences to and involved a different mechanism from the intervocalic consonant deletion seen in the development of to, which could occur word-finally. Like de Chene, considers it possible that became by means of vocalization of, as in. De Chene interprets the use in Heian-era texts of the "mu" kana in the spelling of words like "yomutaru" as an orthographic device representing moraic ; the following examples illustrate the development of u-onbin according to this approach:

Instead of vowel or consonant deletion, prefers to explain onbin as a consequence of phonetic reduction of both the consonant and vowel, resulting in their fusion into a single phonetic segment : that could then be phonologically reinterpreted as a single phoneme. The following example illustrates Frellesvig's approach to explaining onbin:
*