Rendaku is also systematically blocked if the second element of a compound is a recent loanword into Japanese from a foreign language.
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.
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).
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].
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.
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).
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.
[18] 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.
[19] 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).
The Edo period linguists Kamo no Mabuchi[23][24] (1765) and Motoori Norinaga[25][26] (1767–1798) separately and independently identified the law during the 18th century.
Another important factor affecting the likelihood of rendaku is the etymological source or lexical stratum of the second element of the compound.
[27] One possible reason for the resistance of Sino-Japanese morphemes to rendaku is the greater potential for it to cause homophony in this context.
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).
The relevant context is forms such as 東国 tōgoku (eastern provinces), which appears to display rendaku on its second element 国 koku (country).
[48] 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.
[49] 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'.
[52] Other examples of rendaku affecting "multi-root" elements that are themselves composed of smaller elements include the following:[citation needed] 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."
[57] 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].
[61]) 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.
[62] 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'.
[58] No comparable effect is seen with other consonant sounds that undergo rendaku, since they retain the same place of articulation after the change.
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.
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).
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.
[66] Rendaku may have originated from the fusion of consonants with preceding nasal sounds derived from reduction of the genitive postpositional particle no (の)[67] 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".
[69][70] 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.[71] 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).
[72] 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'.
[76] 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'.