# Rendaku

Rendaku (連濁, Japanese pronunciation:, lit. 'sequential voicing') is a pronunciation change seen in some compound words in Japanese. When rendaku occurs, a voiceless consonant (such as /t k s h/) is replaced with a voiced consonant (such as /d ɡ z b/) at the start of the second (or later) part of the compound. For example, the morpheme kami (paper) starts with the voiceless consonant /k/ when used as an independent word or as the first part of a compound word, but this is replaced with the corresponding voiced consonant /ɡ/ in the compound word origami, from ori (fold) + kami.
Rendaku is common in Japanese, but does not occur in all compound words. It is regularly blocked in certain circumstances. The most important phonological condition blocking rendaku is known as Lyman's law, which prevents rendaku if the second element of the compound word already contains one or more of the voiced obstruent consonant phonemes /d ɡ z b/. Rendaku is also systematically blocked if the second element of a compound is a recent loanword into Japanese from a foreign language. Furthermore, rendaku may fail to occur even in contexts where no definite blocking factor is present.
In the Japanese writing system, rendaku affects how a morpheme is spelled when using one of the kana syllabaries: it causes the dakuten ("voicing mark", written as ゛) to be added to the upper right corner of the kana character representing the first consonant and vowel in the second element of the compound. For example, kami and origami are spelled in hiragana as かみ and おりがみ, respectively. Rendaku is not marked in writing when a morpheme is spelled using kanji (logographs taken from Chinese characters). For example, kami (paper) is written with the kanji character 紙, which is unchanged when used in the spelling of origami (折り紙).
Linguistically, since rendaku involves aspects of both pronunciation (phonology) and word structure (morphology), it is categorized as a morphophonological phenomenon.

## Effects

Consonants (in Hepburn) undergoing rendaku :
| Unvoiced | | Voiced |
| k | → | g |
| s, sh | → | z, j |
| t, ch, ts | → | d, j, z |
| h, f | → | b |
Rendaku replaces a voiceless obstruent consonant with a voiced consonant sound. For example, the voiceless alveolar plosive [t] becomes the voiced alveolar plosive [d] in the context of rendaku. In this case, the new consonant retains the same manner and place of articulation as the original consonant. However, rendaku can also cause additional changes depending on the sounds involved.
In the context of Japanese phonology, some consonant sounds that seem distinct to English speakers, and that have distinct spellings in Hepburn romanization, are analyzed as allophones (contextual variants of a phoneme). The following table describes the effects of rendaku in the standard variety of Japanese, using both phonemic transcriptions (marked by slashes, such as /s/) and phonetic transcriptions (marked by square brackets, such as [ɕ]).
Consonants eligible for rendaku :
| Original consonant | Original consonant | Original consonant | Consonant after rendaku | Consonant after rendaku | Consonant after rendaku |
| Phoneme | Allophones | Romanization | Phoneme | Allophones | Romanization |
| /t/ | [t] | t | /d/ | [d] | d |
| /t/ | [ts] | ts | /d/ or /z/ | [dz] or [z] | z |
| /t/ | [tɕ] | ch | /d/ or /z/ | [dʑ] or [ʑ] | j |
| /s/ | [s] | s | /z/ | [dz] or [z] | z |
| /s/ | [ɕ] | sh | /z/ | [dʑ] or [ʑ] | j |
| /k/ | [k] | k | /ɡ/ | [ɡ] or [ŋ] | g |
| /h/ | [ɸ] | f | /b/ | [b] | b |
| /h/ | [h] | h | /b/ | [b] | b |
| /h/ | [ç] | h | /b/ | [b] | b |
Depending on accent, the voiced velar nasal [ŋ] may be used in Japanese as an alternative to the voiced velar stop [ɡ] when the consonant occurs in the middle of a word. These two sounds are typically analyzed as allophones of a single phoneme /ɡ/. In accents that use [ŋ] like this, [k] is replaced with [ŋ] in the context of rendaku.
The voiceless affricates [ts tɕ] are commonly analyzed as allophones of /t/. The phonemic analysis of their voiced outcomes is complicated by a phonetic merger. Originally, [ts tɕ] corresponded to voiced affricate sounds [dz dʑ], whereas [s ɕ] corresponded to voiced fricative sounds [z ʑ]. However, the historical distinction between [dz dʑ] and [z ʑ] has been lost in the Tokyo-based standard (though not in all regional varieties of Japanese). The merged sounds may be pronounced either as voiced affricates or voiced fricatives, regardless of etymology (see yotsugana). As a result of this merge, the phonetic sequence [(d)zɯ] represents a neutralization of historical /du/ and /zu/, and [(d)ʑi] represents a neutralization of historical /di/ and /zi/.
In the context of rendaku, dialects with the merger may be analyzed as possessing an underlying phonemic distinction between /du di/ and /zu zi/ that becomes neutralized on the phonetic level as [dzɯ dʑi]. When morphemes that begin with the morae chi (ち/チ) and tsu (つ/ツ) undergo rendaku, the resulting morae ji and zu are generally spelled with the kana ぢ/ヂ and づ/ヅ, rather than the identically pronounced じ/ジ and ず/ズ. This is not a strict rule, however, and is relaxed in certain older compounds or names, especially those that are not easily recognized as compounds.
It is possible to characterize rendaku in terms of its effect on a morpheme's Japanese kana spelling: it adds the dakuten (voicing mark) to the first kana of the affected morpheme. The relevant graphemes are shown in the tables below (excluding yōon digraphs, which are formed by taking an i-column kana and placing a small ya, yu, or yo kana after it).
Hiragana monographs (gojūon) affected by rendaku :
| | Before rendaku | Before rendaku | Before rendaku | Before rendaku | Before rendaku |
| | a | i | u | e | o |
| K | か ka | き ki | く ku | け ke | こ ko |
| S | さ sa | し shi | す su | せ se | そ so |
| T | た ta | ち chi | つ tsu | て te | と to |
| H | は ha | ひ hi | ふ fu | へ he | ほ ho |
| | After rendaku (with dakuten) | After rendaku (with dakuten) | After rendaku (with dakuten) | After rendaku (with dakuten) | After rendaku (with dakuten) |
| | a | i | u | e | o |
| G | が ga | ぎ gi | ぐ gu | げ ge | ご go |
| Z | ざ za | じ ji | ず zu | ぜ ze | ぞ zo |
| D | だ da | ぢ ji | づ zu | で de | ど do |
| B | ば ba | び bi | ぶ bu | べ be | ぼ bo |
Katakana monographs (gojūon) affected by rendaku :
| | Before rendaku | Before rendaku | Before rendaku | Before rendaku | Before rendaku |
| | a | i | u | e | o |
| K | カ ka | キ ki | ク ku | ケ ke | コ ko |
| S | サ sa | シ shi | ス su | セ se | ソ so |
| T | タ ta | チ chi | ツ tsu | テ te | ト to |
| H | ハ ha | ヒ hi | フ fu | ヘ he | ホ ho |
| | After rendaku (with dakuten) | After rendaku (with dakuten) | After rendaku (with dakuten) | After rendaku (with dakuten) | After rendaku (with dakuten) |
| | a | i | u | e | o |
| G | ガ ga | ギ gi | グ gu | ゲ ge | ゴ go |
| Z | ザ za | ジ ji | ズ zu | ゼ ze | ゾ zo |
| D | ダ da | ヂ ji | ヅ zu | デ de | ド do |
| B | バ ba | ビ bi | ブ bu | ベ be | ボ bo |
The following table shows an example of rendaku for each major allophone of the eligible consonant sounds:
Rendaku examples :
| Change | Example |
| [t] t → [d] d | hi (ひ, fire) + tane (たね, seed) → hidane (ひだね, spark) |
| [ts] ts → [(d)z] z | ari (あり, ant) + tsuka (つか, mound) → arizuka (ありづか, anthill) |
| [tɕ] ch → [(d)ʑ] j | hana (はな, nose) + chi (ち, blood) → hanaji (はなぢ, nosebleed) |
| [s] s → [(d)z] z | kuro (くろ, black) + satō (さとう, sugar) → kurozatō (くろざとう, brown sugar) |
| [ɕ] sh → [(d)ʑ] j | tate (たて, vertical) + shima (しま, stripe) → tatejima (たてじま, vertical stripe) |
| [k] k → [ɡ~ŋ] g | te (て, hand) + kami (かみ, paper) → tegami (てがみ, letter) |
| [ɸ] f → [b] b | kawa (かわ, river) + fune (ふね, boat) → kawabune (かわぶね, river boat) |
| [h] h → [b] b | se (せ, back) + hone (ほね, bone) → sebone (せぼね, backbone) |
| [ç] h → [b] b | hana (はな, flower) + hi (ひ, fire) → hanabi (はなび, firework) |

## Conditions

Rendaku occurs most frequently in compounds where the second element is a single morpheme of native Japanese origin that does not already contain a voiced obstruent phoneme. However, even though rendaku is usual in this context, it does not invariably occur: there are numerous exceptions pronounced without rendaku. Some compound words are pronounced with rendaku by some speakers, but without it by other speakers.
Rendaku is blocked when a voiced obstruent phoneme is already present in the second element of the compound. This rule, called Lyman’s law, is highly reliable, with only a small number of exceptions.
Rendaku is also blocked if the second element is a recent loanword from a language other than Chinese (gairaigo). This rule likewise has few exceptions.
Rendaku does not affect most Sino-Japanese elements, but this tendency is less consistent. A substantial minority do undergo rendaku as the second element of a compound. It has been speculated that Sino-Japanese elements that can undergo rendaku might have become "vulgarized", that is, adopted into the same category of vocabulary as native Japanese morphemes.
Other rules have been proposed regarding circumstances where rendaku is either blocked or favored, but often, it is only possible to identify tendencies rather than inviolable rules.

### Lyman's law

Lyman's law is the constraint that rendaku cannot occur if the second element already contains a voiced obstruent phoneme (that is, if it contains any of the consonant phonemes /d ɡ z b/, including their allophones such as [dʑ] and [ŋ]; all of these sounds are written with the dakuten and called "muddy sounds" (濁音, dakuon) in Japanese). This is considered to be one of the most fundamental of the rules governing rendaku.
    yama + kado → Yamakado (surname) 山門（やまかど） ("mountain" + "gate" → place name). Since kado already contains a voiced obstruent consonant phoneme /d/, its initial consonant /k/ does not undergo rendaku, so the form *Yamagado やまがど does not exist (* indicates a non-existent form).
    hitori + tabi → hitoritabi ("one person" + "travel" → "traveling alone"), not *hitoridabi. Since tabi already contains a voiced obstruent consonant phoneme /b/, its initial consonant /t/ does not undergo rendaku.
    yama + kaji → yamakaji ("mountain" + "fire" → "mountain fire"), not *yamagaji. Since kaji already contains a voiced obstruent consonant phoneme /z/ (in the form of its allophone j [(d)ʑ]), its initial consonant /k/ does not undergo rendaku.
The precise formulation of Lyman's law varies between analysts. In particular, there are conflicting viewpoints on the size of the phonological domain in which it applies. One formulation states that rendaku is blocked by the presence of voiced obstruent consonant "within a morpheme"; this may be interpreted as a consequence of a more general constraint that applies also to the underived form of native Japanese morphemes, which do not generally contain more than one voiced obstruent phoneme. An alternative view is that Lyman's law applies whenever a voiced obstruent consonant occurs anywhere within the second element of a compound, and so might also include cases where this element is composed of more than one morpheme. Rendaku occasionally (although relatively infrequently) causes voicing of the initial consonant of a Sino-Japanese (kango) lexeme that is written with two kanji, and is in etymological terms composed of two Sino-Japanese roots; it is debatable whether such lexemes count as one morpheme or two from a synchronic perspective.
In modern Japanese, the presence of a voiced obstruent phoneme in the first element does not normally block rendaku, as demonstrated by examples such as sode (そで, sleeve) + kuchi (くち, mouth) → sodeguchi (そでぐち, cuff). Nevertheless, it has been proposed that in certain circumstances, Lyman's law might be (or might once have been) sensitive to the presence of a voiced obstruent in the first element of a compound. Compound personal names ending in the element ta 'rice field' seem to usually show rendaku when the final mora of the first element contains /t k s m n/ (e.g. Katada, Fukuda, Asada, Hamada, Sanada), but never show rendaku when the final mora of the first element contains /d ɡ z b j/ (e.g. Kadota, Nagata, Mizuta, Kubota, Hayata) (and usually do not show rendaku when it contains /r w/). The pattern of voicing seen in compounds like these may in part be a residue of an older version of the law that operated in Old Japanese. Examination of Old Japanese compounds suggests that Old Japanese had a constraint against two consecutive syllables starting with a prenasalized consonant (the source of modern Japanese dakuon/voiced obstruent phonemes), but over time, this constraint came to be replaced with the modern tendency for a dakuon consonant to block rendaku only when it occurs in the second element of the compound.
Some formulations of the law treat it as applicable only in cases where the dakuon/voiced obstruent phoneme is the second consonant of the final element of the compound. In the case of Old Japanese, there is not enough evidence to conclude whether the Old Japanese version of Lyman's law applied to morphemes containing a prenasalized consonant in their third or later syllable. In modern Japanese, however, there is evidence that Lyman's law applies in general to morphemes of this form, as indicated by the lack of rendaku in examples such as tsuno (つの, horn) + tokage (とかげ, lizard) → tsunotokage (つのとかげ, horned toad) or ko (こ, child) + hitsuji (ひつじ, sheep) → kohitsuji (こひつじ, lamb). There are only a handful of exceptions, such as nawa (なわ, rope) + hashigo (はしご, ladder) → nawabashigo (なわばしご, rope ladder), where voicing occurs despite the presence of a dakuon/voiced obstruent consonant in the second element of the compound.
Although this law is named after Benjamin Smith Lyman, who independently propounded it in 1894, it is really a re-discovery. The Edo period linguists Kamo no Mabuchi (1765) and Motoori Norinaga (1767–1798) separately and independently identified the law during the 18th century.

### Lexical stratum of the second element

Another important factor affecting the likelihood of rendaku is the etymological source or lexical stratum of the second element of the compound. Rendaku frequently affects wago (native Japanese lexemes), infrequently affects kango (Sino-Japanese vocabulary), and very rarely affects gairaigo (recent loanwords, such as borrowings from English). On the other hand, the lexical stratum of the first element of the compound is not relevant.
One possible reason for the resistance of Sino-Japanese morphemes to rendaku is the greater potential for it to cause homophony in this context. Native Japanese morphemes very rarely start with a voiced obstruent consonant, but this does not apply to Sino-Japanese; therefore, rendaku of Sino-Japanese morphemes is more likely to neutralize a contrast between distinct morphemes.

#### Kango

Sino-Japanese vocabulary is built from Sino-Japanese roots, which have a restricted phonological structure (one or two moras long). At least half or more of Sino-Japanese terms are "binoms" consisting of two roots, but some roots can be used on their own as words (mononoms). Each word is written with as many kanji (Chinese characters) as it has roots.
When used as the second element of a compound, most Sino-Japanese lexemes do not undergo rendaku. However, a minority (around 20% of mononoms, and 10% of binoms) do show rendaku in at least some compounds. No criteria have been identified that predict with 100% accuracy when this occurs.
In terms of phonology, rendaku is blocked by Lyman's law and so never affects a binom where the second root starts with a voiced obstruent phoneme; e.g. kōzō (構造) in shakaikōzō (社会構造, social structure), honzan (本山) in sōhonzan (総本山, head temple). Based on a study of how native speakers pronounced novel compounds, Low 2009 concluded that rendaku is statistically less likely to affect a Sino-Japanese binom where the first root ends in the moraic nasal /N/ and the second root end in a voiceless obstruent, although it is not fully blocked in this context (the study's observed rate of rendaku in this context was 1.3%, compared to Vance 1996's dictionary-based estimate of rendaku affecting 10% of all Sino-Japanese binoms).
Examples of rendaku in compounds ending in a Sino-Japanese mononom :
| Kanji | Romanization | Translation |
| 火 + 鉢 → 火鉢 | hi + hachi → hibachi | "fire" + "bowl" → "brazier; hibachi" |
| 寝 + 相 → 寝相 | ne + sō → nezō | "sleep" + "appearance" → "sleeping posture" |
Examples of rendaku in compounds ending in a Sino-Japanese binom :
| Kanji | Romanization | Translation |
| 親 + 会社 → 親会社 | oya + kaisha → oyagaisha | "parent" + "company" → "parent company" |
| 株式 + 会社 → 株式会社 | kabushiki + kaisha → kabushikigaisha | "stock-type" + "company" → "joint-stock company" |
| 客 + 布団 → 客布団 | kyaku + futon → kyakubuton | "guest" + "bedding" → "bedding for guests" |
Sino-Japanese roots that start with voiceless obstruents may have variant pronunciations starting with voiced obstruent phonemes for other reasons aside from rendaku.
One reason is the existence of different readings of Sino-Japanese roots, corresponding in general to different time periods of borrowing. Two of the most important types of reading are termed Go-on and Kan-on. Certain Kan-on readings starting with /h t s k/ correspond regularly to Go-on readings starting with /b d z ɡ/: these represent different adaptations of Early Middle Chinese voiced obstruent sounds, and so the existence of these alternative pronunciations is unrelated in origin to rendaku.
An example is the root 地 'ground, land', which has both a Kan-on pronunciation chi [tɕi] and a Go-on pronunciation ji [(d)ʑi]; for this reason, the use of the voiced pronunciation in compounds such as roji (路地, lane, alley) cannot necessarily be attributed to rendaku, since the ji version of this root can also be found at the start of a word, e.g. in jishin (地震, earthquake).
In addition, a minority of lexemes composed of two Sino-Japanese roots display a type of sequential voicing, affecting only roots in second position, that is indistinguishable in effect from rendaku, but probably has a distinct origin in terms of morphology. The relevant context is forms such as 東国 tōgoku (eastern provinces), which appears to display rendaku on its second element 国 koku (country). In this case, voicing is hypothesized to be the result of the preceding Sino-Japanese root 東 originally ending in a nasal sound, which caused the following consonant to become prenasalized and voiced. Prenasalization and voicing of a consonant after a nasal sound (/ũ, ĩ, N/) is hypothesized to have been an active phonological rule up through Early Middle Japanese; in Late Middle Japanese, /ũ, ĩ/ were denasalized and voicing after /N/ ceased to be automatic.

#### Gairaigo

Gairaigo vocabulary is usually not affected by rendaku when it occurs as the second element of a compound, as illustrated by the contrast between garasudana 'glass shelf', from native Japanese tana 'shelf', and garasukēsu 'glass case', from foreign kēsu 'case': rendaku does not occur and is not expected to occur in the latter compound word, since its non-initial element belongings to foreign vocabulary. (In contrast, as shown by garasudana, the use of a gairaigo word as the first element of a compound does not prevent rendaku of a following native element.) Examples where rendaku affects a gairaigo element of a compound are highly exceptional.

### Part of speech

Rendaku affects compounds involving various parts of speech, such as Noun + Verb, Adjective + Noun, Verb + Noun, Verb + Adjective; however, it is rare in compounds of the form Verb + Verb.
Noun + na-adjective/noun → noun :
| Hiragana | Romanization | Translation |
| おんな + すき → おんなずき | onna + suki → onnazuki | "female person" + "liking; fondness" → "fondness for women; woman lover" |
| おとこ + きらい → おとこぎらい | otoko + kirai → otokogirai | "male person" + "dislike; hatred" → "dislike for men; misandry" |
Ending in i-adjective → i-adjective :
| Hiragana | Romanization | Translation |
| うす- + きたない → うすぎたない | usu- + kitanai → usugitanai | "faint-; light-" + "dirty" → "dirty" |
| くち + きたない → くちぎたない | kuchi + kitanai → kuchigitanai | "mouth" + "dirty" → "foulmouthed; scurrilous" |
Noun + verb → verb :
| Hiragana | Romanization | Translation |
| め + ふく → めぶく | me + fuku → mebuku | "sprout" + "to blow" → "to bud" |
Verb (ren'yōkei) + noun → noun :
| Hiragana | Romanization | Translation |
| いけ + はな → いけばな | ike + hana → ikebana | "keep alive" + "flower" → "flower arrangement" |
| おり + かみ → おりがみ | ori + kami → origami | "fold" + "paper" → "paperfolding" |
Verb (ren'yōkei) + verb → verb :
| Hiragana | Romanization | Translation |
| たち + とまる → たちどまる | tachi + tomaru → tachidomaru | "standing; starting; igniting" + "to stop" → "to stop" |
Verb (ren'yōkei) + verb (ren'yōkei) → noun :
| Hiragana | Romanization | Translation |
| おき + さり → おきざり | oki + sari → okizari | "putting" + "leaving" → "deserting" |
| くるい + さき → くるいざき | kurui + saki → kuruizaki | "being in disarray" + "blooming" → "unseasonable blooming" |

### Reduplication

Rendaku is very frequent in words formed by reduplication, other than mimetic words, which are immune to rendaku.
Examples:
    ひと + ひと → ひとびと (人々) (iteration)
       hito + hito → hitobito ("person" + "person" → "people")
    とき + とき → ときどき (時々) (iteration)
       toki + toki → tokidoki ("time" + "time" → "sometimes")

### Semantics

Rendaku tends not to occur in non-reduplicative compounds which have the semantic value of "X and Y" (so-called dvandva or copulative compounds), as exemplified by yama + kawa > yamakawa "mountains and rivers", as opposed to yama + kawa > yamagawa "mountain river".

### Branching compounds

In compounds containing more than two elements (or rather, compounds where one element is itself a compound), the branching structure of the compound may affect the application of rendaku. For example, todana, a compound of the morphemes to "door" and tana "shelf", retains its initial voiceless /t/ when used as the second element of the compound fukurotodana "small cupboard". In examples like this, where the second element contains a voiced consonant as a result of rendaku, the lack of voicing at the start of the second element of the larger compound can potentially be explained as a consequence of Lyman's law.
Otsu 1980 proposed that rendaku is blocked in general in the left-branching elements of a right-branching compound, even in cases where Lyman's law does not apply. However, other linguists have questioned the validity or necessity of formulating such a constraint. The branching constraint is intended to explain the contrasting behavior of examples such as the following:
    mon + [shiro + chō] > monshirochō, not *monjirochō ("family crest" + ["white" + "butterfly"] > "cabbage butterfly")
but
    [o + shiro] + washi > ojirowashi (["tail" + "white"] + "eagle" > "white-tailed eagle")
This constraint does not apply to all words where the second element is composed of more than one morpheme. As discussed above, rendaku can affect Sino-Japanese "binoms" composed of two Sino-Japanese roots. Assuming the branching constraint is valid, it is possible it does not prevent rendaku in that context because Sino-Japanese binoms do not have the morphological status of compound words in the context of rendaku. In any case, there seem to be some counterexamples to the branching constraint, such as ōburoshiki 'big talk', from ō- 'big' + furoshiki, from furo ' bath' + shiki 'carpet', or machibikeshi 'fire brigade for common people', from machi 'town' + hikeshi, from hi 'fire' + keshi 'to extinguish'. One proposal accounts for such apparent counterexamples by postulating a distinction between "loose" compounds, which are hypothesized to be immune to rendaku per the branching rule when used as the right-hand element of a larger compound, and "strict" compounds, which can undergo rendaku the same way as single morphemes. However, it is not clear that there are reliable non-circular criteria for predicting whether a compound is "loose" or "strict". Other examples of rendaku affecting "multi-root" elements that are themselves composed of smaller elements include the following:
    おぼろ + つきよ → おぼろづきよ
       oboro + tsukiyo → oborozukiyo ("haze" + "moonlit night" → "hazy moonlit night")
          Here, tsukiyo is composed of tsuki ("moon") and yo ("night")
    いろ + ちゃや → いろぢゃや
       iro + chaya → irojaya ("lust" + "teahouse" → "brothel teahouse")
          Here, chaya is composed of cha ("tea") and ya ("shop"); cha by itself generally doesn't undergo rendaku, but chaya frequently does
The branching constraint analysis could be considered a violation of the Atom Condition, which states that "in lexical derivations from X, only features realized on X are accessible." An alternative view proposes that the process applies cyclically.
    [nuri + hashi] + ire > nuribashiire ([lacquered chopstick] case, "case for lacquered chopsticks")
    nuri + [hashi + ire] > nurihashiire (lacquered [chopstick case], "lacquered case for chopsticks")
This could be seen as the voicing between hashi and ire staying unrealized but still activating Lyman's Law.
Ito and Mester 2003 proposed a third account distinct from both Otsu 1980's branching-based constraint and Ito and Mester 1986's cyclical account. This hypothesis holds that the relationship between branching and rendaku is not direct, but is mediated by prosodic structure: the lack of rendaku in right-branching compounds such as hatsu kao awase is analyzed as a consequence of kao coming at the start of a prosodic word. Per Ito and Mester 2007, whether a compound is treated as one or as multiple prosodic words is affected by the length of the second element of the compound: if the second element is longer than four moras (or two bimoraic feet), then the compound is required to have the prosody of a phrase rather than a single word.

### Further considerations

Despite a number of rules which have been formulated to help explain the distribution of the effect of rendaku, there still remain many examples of words in which rendaku manifests in ways currently unpredictable. Some instances are linked with a lexical property as noted above but others may obey laws yet to be discovered. Rendaku thus remains partially unpredictable, sometimes presenting a problem even to native speakers, particularly in Japanese names, where rendaku occurs or fails to occur often without obvious cause. In many cases, an identically written name may either have or not have rendaku, depending on the person. For example, 中田 may be read in a number of ways, including both Nakata and Nakada.
In some cases, rendaku varies depending on syntax. For instance, the suffix tōri (〜通り, "road, following"), from tōru (通る, "to go, to follow"), is pronounced as -tōri (〜とおり) following the perfective verb, as in omotta-tōri (思った通り, "as I thought"), but is pronounced as -dōri (〜どおり, with rendaku) when following a noun, as in yotei-dōri (予定通り, "as planned, according to schedule") or, semantically differently – more concretely – Muromachi-dōri (室町通, "Muromachi Street").

#### Lexical propensity

It has been hypothesized that morphemes are inherently either more susceptible or more resistant to being voiced when used as the second element of a compound; in other words, that the propensity of a morpheme to undergo rendaku is lexically specified. Some morphemes show voicing in all compounds in which they occur. At the far end of the spectrum, a small percentage of morphemes appear to be immune to rendaku (for reasons not explained by the phonological, morphosyntactic, and lexical-stratum factors described above that regularly block rendaku). Other morphemes are intermediate and undergo voicing in some but not all compounds. Irwin 2016 found that out of elements that occurred at least 5 times in second position in a database of frequent compound words, the most common behavior (42%) was to undergo voicing in all compounds, and each range of greater resistance to rendaku contained successively fewer elements (35% had voicing rates from 0.667 to 0.999; 12% had voicing rates from 0.334 to 0.666; 7% had voicing rates from 0.001 to 0.333, and 5% were never voiced).
Rosen 2016 suggests that the first element of compound words also has a lexically variable propensity to trigger rendaku, hypothesizing that rendaku occurs in words where the combination of these two voicing weights (the rendaku-triggering weight of the first element and the rendaku-undergoing weight of the second element) exceeds a threshold value, and fails to occur when this value falls below the threshold.

#### Avoidance of bVmV

Rendaku seems to be avoided in non-verbal elements that start with [h] or [ç] + vowel + /m/ + vowel, such as hama, hamo, hima, hime, himo, hema, which has been explained as an effect of a preference against having homorganic consonants at the start of adjacent syllables: rendaku would replace [h] or [ç] with [b], which is bilabial like [m]. Rendaku is seen before vowel + /m/ + vowel in koibumi 'love letter' from fumi 'letter': this is consistent with the hypothesis, since [ɸɯmi] contains [ɸ], which is already homorganic with [m] (and so avoiding rendaku would not make any difference). (An alternative explanation supposes that fumi, as well as other words that undergo rendaku to /b/, starts with an underlying labial consonant that is phonologically distinct from the /h/ found at the start of lexemes that do not undergo rendaku.)
A study observed this tendency as an active factor affecting the frequency with which Japanese speakers preferred rendaku vs. non-rendaku variants of nonce words.
For whatever reason, this avoidance is not seen in verb roots (including deverbal nouns), which undergo rendaku even in cases such as musibamu 'to corrupt'.
No comparable effect is seen with other consonant sounds that undergo rendaku, since they retain the same place of articulation after the change.

## Productivity

Although rendaku does not occur in all compounds, it is common and studies of Japanese native speakers show that it occurs often in newly formed compounds. It has been suggested that its productivity in new compounds is caused by analogy with existing compound words.

### Acquisition by children

Some studies have examined the phonological development of rendaku. Studies from the late 1990s and early 2000s indicate that children under five and a half years old show limited use of rendaku in any context. The use of rendaku in established compounds becomes frequent by the age of six, but children below this age do not show reliable use of rendaku in unfamiliar compounds. Children over the age of six use rendaku frequently both in familiar and unfamiliar compounds.

## Theoretical analysis

In linguistics, rendaku has been analyzed in terms of various phonological theories. It has been popular to identify Lyman's Law, the restriction against applying rendaku to a morpheme that already contains a voiced obstruent phoneme, as an example of a more general theoretical concept known as the obligatory contour principle (or "OCP" for short). This principle was originally formulated (by Leben 1973) to refer to the phonology of tone, and referred to a hypothesized constraint against having consecutive identical tones in the underlying representation of a morpheme. Later phonologists have interpreted the principle as a more general constraint, using it to refer also to bans on identical adjacent specifications of various non-tone features. Thus, Lyman's Law has been interpreted as an example where the obligatory contour principle (OCP) applies to voicing specifications and rules out multiple occurrences of voicing within a morpheme.

## Historical origin

The voiced obstruent consonants of modern Japanese go back to prenasalized voiced obstruents of Old Japanese. Rendaku may have originated from the fusion of consonants with preceding nasal sounds derived from reduction of the genitive postpositional particle no (の) or the dative postpositional particle ni (に): for example, according to this hypothesis, a form such as yamadori (やまどり, copper pheasant) might go back to an original yama-no-tori "mountain-GEN bird". This explanation could help account for why rendaku is not found consistently in all compound words: if some compounds were originally formed with no or ni, but others were formed with simple juxtaposition of two roots, then rendaku would be expected to have arisen only in the first category of compounds, but not in the second.
Whatever its origin, by the Old Japanese period rendaku had already become grammatically distinct from constructions with no or ni, as shown by the occurrence of forms such as nadori "your bird", where a phrase with no would be ungrammatical, since the genitive of the pronoun na "you" was always formed with the particle ga.

## Rendaku in Tohoku dialects

In the Kahoku dialect of Tōhoku, the phonemes /t k ts tɕ/ have voiced allophones [d ɡ dz dʑ] when they come between voiced vowels, and the phonemes /b d ɡ z dʑ/ have prenasalized or nasal allophones [ᵐb ⁿd ᵑɡ~ŋ ⁿdz ⁿdʑ] when they come between vowels: for example, /mato/ 'target' is pronounced [mɑdo] (with a second consonant that is voiced but not prenasalized) whereas /mado/ 'window' is pronounced [mɑ̃ⁿdo] (with both voicing and prenasalization of the second consonant). Thus, rendaku in this dialect, when it occurs, typically involves phonetic prenasalization of the second element of the compound, as is speculated to have been the case in prehistoric Japanese: e.g. /hama/ 'beach" + /kuri/ 'chestnut' → /hamaɡuri/ [hɑmɑ̃ᵑɡɯɾɨ] 'clam'. However, the use of prenasalization at the start of the second element of a compound word is not uniform, and depending on the speakers and the words pronounced, significant variations were observed. There was a relationship between the rate of prenasalization and the speakers’ age: older individuals use prenasalized pronunciations at a higher rate than younger individuals. On the other hand, differences in the speakers’ gender and socioeconomic status did not affect the rate of prenasalization. It is speculated that dialect mixing with standard Japanese may have increased the use of pronunciations without prenasalization. In the case of /b/ [ᵐb], loss of prenasalization may also have additionally been facilitated by the fact that the resulting sound [b] did not merge with any preexisting phoneme, since /p/ does not occur intervocalically in non-mimetic vocabulary (in contrast, in forms like [te̝ɡɑmɨ], the absence of prenasalization makes it possible to interpret the consonant [ɡ] as merely the voiced intervocalic allophone of /k/, which would result in the phonemic transcription /tekami/, with the same consonant phoneme as the independent word /kami/).
A Tōhoku dialect spoken in Iwate Prefecture has been reported to have a phonotactic constraint prohibiting prenasalized obstruents from occurring in two successive syllables; this rule produces regular denasalization in [kɑ̃ᵐbɑbɨ] 'ceremonial fire' as opposed to [hɑnɑ̃ᵐbi] 'fireworks'.