Language scratchpad/Altlangs/Alternate reconstructions/Proto-Japonic scratchpad

This subarticle lists some of my notes on Proto-Japonic. See also my /Proto-Ryukyuan scratchpad/.

Disclaimer: The entirety of this article's contents is to be considered science fiction. They are not, in any way, verified and accepted reconstructions of real-life proto-languages, even if they are largely based on accepted reconstructions.

Consonants
I reconstruct the following consonant inventory for Proto-Japonic:

The pronunciations of these consonants generally follow the IPA. However:
 * */r/ varied between *[l], *[ɾ] and *[r].
 * The exact pronunciation of */s/ is a matter of debate among Japanese linguists, due to the order of the gojūon placing /s/ before /t/ (the original order in Sanskrit placed /s/ with the other fricatives at the end). While it is fairly simplistic to reconstruct *[t͡s], this conflicts with the fact that almost all Japonic languages feature [t͡s] as a reflex of */t/ before */u/.
 * I don't confidently postulate any full palatalisation, even of */s/, before */i/. While the sequence /si/ does have a strong tendency to palatalise, the daughter languages do not agree on which environment causes palatalisation. While Japanese and Okinawan palatalise their reflexes of */s/ before */i/, Miyako only does so before its reflex of */e/. However, depalatalisation before non-front vowels is possible, and since Proto-Japonic */i/ became Miyako /ɨ/, it is possible that a former *[ɕi] depalatalised to [s] (also note the elision of /ɨ/).
 * Tentatively, I have the following allophones for */s/ and */t/:
 * */t/ is [t] before all vowels except */u/, in which case it is [t͡s], and */i/, in which case it is *[t͡ɕ].
 * */s/ is [t͡s] before */a/, *[ɕ] before front vowels, and *[s] before rounded vowels.

Voiced consonants in the daughter languages are typically reflexes of a nasal + obstruent consonant cluster.

The outcome of each consonant sequence is listed below:

Vowels
I reconstruct six vowels for Proto-Japonic:

I confidently reconstruct the diphthongs */ui̯/, */oi̯/, */əi̯/ and */ai̯/, and tentatively reconstruct */ei̯/ and */au̯/. In addition, the vowels */a/ and */ə/ may be preceded by the glide */j/, and the former by */w/ (**/wə/ is prohibited by Arisaka's Law).

I reconstruct a rounded vowel for */ə/ due to its reflexes in Japanese and Ryukyuan. Bentley (2001) asserts that it must be an unrounded schwa based on correspondences between Sino-Japanese and Sino-Vietnamese, but I don't find such evidence convincing due to my perception on the acoustics of [ə] and [ɵ]. To me, both [ə] and [ɵ] sound quite similar (but not identical) to each other and to [ø] and [œ], so all I can say is that Proto-Japonic */ə/ is a schwa-like sound. (On the topic, can anyone tell the difference between the New Zealand pronunciation of bird, which features a rounded vowel, and the Received Pronunciation version of the same word, which features an unrounded vowel?)

Arisaka's Law dictates that */ə/ cannot co-occur with a back vowel in the same morpheme. I believe that this is a remnant of an older vowel harmony system that operated in the ancestor of Insular Japonic (whether it was in Peninsular Japonic, I do not know, due to lack of evidence). Traces of this system can be found in the numerals, with */i/ alternating with */u/ and */ə/ alternating with */a/. Given these alternations, I tentatively reconstruct the vowel harmony system that was in use: To arrive at the current six-vowel system, *[ə] and *[ø] merged to become */ə/, and *[i] and *[y] merged to become */i/. Hence, if my hypothesis is correct, there should be an alternation between */o/ and */ə/ (which would arise in Old Japanese as an alternation between u/o1 and o2). So far, I've yet to find any convincing evidence of such an alternation.

The general outcome of each vowel is as follows:

In general, Proto-Japonic */e/ and */o/ are raised to /i/ and /u/ respectively in non-word-final position in Japanese. However, there are some exceptions where original */o/ is retained (the following list is non-exhaustive; I don't know if the same applies to */e/): With one exception (that being yoru), every word I've found has an /a/ occurring after the syllable with /o/ (*/ə/ is ruled out by Arisaka's Law). Therefore, I suspect that the vowel raising in Japanese may in fact be an umlaut process, where /a/ blocks raising (for the only counterexample I know, *koma → kuma, my reconstruction is tentative). The word yoru is the exception because it is bimorphemic; the actual root is *yo, leading to the count form -yo, where the /o/ is expected.
 * sora ("sky"), from *sora
 * yoru ("night"), from *yo-ru
 * tora ("tiger"), from *tora
 * moya ("mist"), from *moya
 * yowai ("weak"), from *yowa-
 * osanai ("very young"), from *wosana-

All examples I've found so far are either bisyllabic or feature /a/ in both the second and third syllables. I am unsure if the same blocking applies if the second syllable is */a/ while the third is not */a/ (the only example of this I've found may be *wosanki → Old Japanese wosagi(1), whence Modern Japanese usagi), or if it is the second syllable that is */o/ and the third syllable */a/.

With regards to */e/, I've only found one possible example of unraised /e/ in Japanese: the word eda ("branch"), from Proto-Japonic *yenta. However, the typical reconstruction is *yonta, as shown in various Ryukyuan forms such as Okinawan yuda. Tentatively, I extend the above hypothesis to */e/, considering that Okinawan also has the variant yida, which indeed comes from *yenta.

The general outcome of each vowel sequence is as follows: There may be some evidence that Proto-Ryukyuan distinguished between the reflexes of *i and *ui/*oi. Old Namari also distinguished between the two, with the latter failing to fully palatalise /t/ and /d/.

As of writing (2019-06-18), I have noticed one Wiktionary user moving a number of Proto-Japonic reconstruction articles with the edit reason "*wə does not exist; it should be *wo". I disagree with this reasoning; for one, if true, this would lead to a violation of Arisaka's Law with regard to the numeral ten (the only way around that is if one interpreteted *təwə as bimorphemic **tə-wo).

Also, I've noticed that the same Wiktionary user assumes that unexplained /o/ in Japanese developed from a supposed **uwa. I completely disagree with this reasoning, as I can easily find a counterexample (Japanese suwaru "to sit", from the root *suwa-). This user used this to explain sora ("sky") and ko ("child"). The former I've given my umlaut explanation, and the latter may be a result of confusion with Northern Ryukyuan, which generally has some variation of kwā (an alternate etymology suggests that this is actually a repurposed plural form).

Pitch and tone
The following is based on Shimabukuro's (2002) reconstruction of the Proto-Japonic accent system. The tone in parentheses represents the tone of the first mora of any following suffix/clitic in the phonological word.

Monosyllables
Monosyllables may have been bimoraic in Proto-Japonic. Thus, all monosyllables featured long vowels (word shape oo instead of short O). The monosyllables develop into three tonal classes in Early Middle Japanese and Proto-Ryukyuan.

For the root shape column, which are my own reconstructions on the possible shape of the Proto-Japonic word, T represents a voiceless consonant, M a voiced consonant, V a vowel, C any consonant or /j/, and N any nasal.

The Namari column indicates the pitch accent shape and class of the reflex.

It is suggested that initial low tone is the result of voiced initials. If so, then example reconstructions of monosyllabic words are as follows:

Although this sample size is small, 1a and 1c tend to correspond to words ending in -y. This may mean that these classes are remnants of a "checked" tonal class.

Disyllables
Shimabukuro reconstructs eight different tonal classes for disyllables, corresponding to five in Early Middle Japanese and three in Proto-Ryukyuan.

Example reconstructions:

(A side note: some of the Namari forms show a sound change unique to the Yaezora dialect, high vowel dissimilation. High vowel dissimilation only affects word-initial /i/ and /u/, and it causes these vowels to lower to /e/ or /o/ respectively whenever they are followed by a mora with /i/ or /u/. Note that original /wi/ is not affected, although the only example I have is ijishi "pig".)

Classes 2g and 2h are hypothesised by Vovin (2008) to have ended in a nasal.

Trisyllables
Shimabukuro reconstructs twelve tonal classes for trisyllables. These classes give seven Early Middle Japanese tonal classes and six Proto-Ryukyuan tonal classes.

Because my word structure reconstructions for trisyllables are tentative, I will omit my Pre-Proto-Japonic reconstructions in the following table.

A side note: The pitch accent of Yaezora dialect has elements of both stress and tone. Each word has an inherent tone (high or low), and a mora in which the tone changes (corresponding to stress, as no word has no accent and only unstressed short /i/ and /u/ can be elided after /s/). Some words also have "secondary stress", where the tone changes back; secondary stress is limited to words with inherent low tone. Yaezora dialect tonal classes are given as X.Y.Z, where X is the number of morae in the word, Y is either L or H for words with inherent low or high tone respectively, or a number to indicate the location of the first tone change, and Z is a number indicating the location of the (second) tone change.

Example of Namari numerals:

Issues with reconstructions

 * In some cases, it is impossible to determine whether a proto-form has */u/ or */o/.
 * So far, I've run into the same problem distinguishing word-initial */i/ from */e/. While I can say with some certainty that "to say" is *ip-, other words may prove more troublesome. What I've noticed that at the very least Proto-Japonic */i/ induces palatalisation of the following consonant in Proto-Ryukyuan; I don't know if this is true for */e/ as well.

Swadesh list
Where a word is given in parentheses, it represents the second principal part of the word preceding it. This appears for all verbs (where it represents the imperative) and all non-first declension and all monomoraic nouns (where it represents the genitive).

Note: Where I have [m,n] it reflects an alternation between Japanese and the Ryukyuan languages between the two consonants:
 * Proto-Japonic *[m,n]ipi becomes Japanese nii but Okinawan miisan.
 * Proto-Japonic *[m,n]inki-ri becomes Japanese migi(ri) but Okinawan nijiri.

Numerals
I have reconstructed the following numerals:

Reconstruction issues
There are a number of unresolved issues when reconstructing Proto-Japonic vocabulary.

Cardinal directions
So far, I have only reconstructed these terms for Proto-Ryukyuan (north: *nisi, east: *aga-r-i, south: *pa(y)e, west: *ir-i), and only if one takes into account the modern languages. The language of the Omoro Sōshi features nishi meaning both "west" (as in Japanese) and "north", as well as the terms kami and shimo for "north" and "south" respectively.

The Japanese terms are in general different from those of the Ryukyuan languages. Japanese still has nishi, but it means "west" instead of "north" (and based on evidence from the Omoro Sōshi, I believe the "west" meaning is the original meaning of Proto-Japonic *nisi). The other three terms do not match with their Ryukyuan counterparts. The terms kita and minami ("north" and "south" respectively) do not have any transparent etymologies (note that Japanese also has hae, meaning "south wind" and cognate with the Ryukyuan terms for "south"), while higashi is of secondary development (a compound of hi "sun" with a form of muku "to face a direction"). Japanese also has azuma ("east"), derived from Old Japanese aduma, but also with an unclear etymology.

Because of these differences, I have had to make my own words for the cardinal directions in Namari (and their corresponding winds, if separate):
 * North: kami (かみ)
 * East: pingai (ひんがい), kochi (こち)
 * South: shimo (しも), pae (はえ)
 * West: nishi (にし)

The derivations are as follows:
 * North: From Proto-Japonic *kami, meaning "upper; northern".
 * East: A compound of Old Namari pi ("sun", from Proto-Japonic *pi) and mukapi, the infinitive of mukapu ("to face a direction", from Proto-Japonic *muk-ap-; compare Okinawan nkayun). Compare Japanese higashi, derived from Old Japanese *pi1-muka-si. The term kochi is of unclear derivation, but does originate from Proto-Japonic *kəti.
 * South: From Proto-Japonic *simo, meaning "lower; southern". The term pae may be an old loanword from Sanskrit (via Chinese), but is reconstructible for Proto-Japonic, the protoform being *paye.
 * West: From Proto-Japonic *nisi, meaning "origin; west"

Family
Reconstructing terms for family and relations have proved very difficult, due to the variation between languages, and even between dialects. So far, I can only reconstruct four words confidently (and several more tentatively) in this semantic category:
 * *əy-a, meaning "parent" (the root *əy-, means "to grow old"; I am unsure whether Japanese oiru "to grow old" corresponds to *əy-əy- or *əy-[u,o]y, due to ambiguities found in what little I've found in Ryukyuan; for Namari I assume *əy-əy-)
 * *amo, meaning "mother" (tentatively, also *papa)
 * *ətə, meaning "younger sibling"
 * *itoko, meaning "cousin" (confirmed by Okinawan ichuku)
 * Tentatively, *sosa, meaning "older sibling"

I can only trace e ("older sibling") to Proto-Japanese (whose form is *ye), but oto ("younger sibling") does go back to Proto-Japonic.

Namari has the following terms:
 * oya (おや), meaning "parent"
 * amo (あも), meaning "mother" (alternatively はは papa, although due to language contact this variant is archaic and easily confused)
 * kazo (かぞ), meaning "father"
 * wayabe (わやべ), meaning "child"
 * oyobe (およべ), meaning "son" (ultimately derived from Old Namari wo- + warabe)
 * maibe (まいべ), meaning "daughter" (ultimately derived from Old Namari me- + warabe)
 * moko (もこ), meaning "son-in-law" (also means "groom", from Proto-Japonic *moko "groom; son-in-law")
 * yome (よめ), meaning "daughter-in-law" (also means "bride", from Proto-Japonic *yəme "bride; daughter-in-law")
 * sosa (そさ), meaning "older sibling" (bound form え e)
 * onnae (おんなえ), meaning "older sister" (derived from onna + -e; colloquially, あね ane or ねー nē)
 * okkonoe (おっこのえ), meaning "older brother" (derived from otoko + -no + -e; colloquially, あに ani or にー nī)
 * oto (おと), meaning "younger sibling"
 * otouto (おとうと), meaning "younger brother"
 * imouto (いもうと), meaning "younger sister"
 * itoko (いとこ), meaning "cousin"
 * pamae (はまえ), meaning "grandmother" (derived from pa- + mae)
 * shimae (しまえ), meaning "grandfather" (derived from shi- + mae)
 * oyamae (おやまえ), meaning "grandparent"
 * mmago (んまご), meaning "grandchild" (tentatively I reconstruct *(m)uman-ko, but most Ryukyuan words are descendants of Proto-Ryukyuan *(m)umaga, with only Yonaguni using *(m)umago)
 * umango (うまんご), meaning "grandson"
 * umamme (うまんめ), meaning "granddaughter"
 * The above six terms may be prefixed with pi- (ひ) to refer to great-grandparents or great-grandchildren. This prefix can be repeated to increase the generational gap by one per repeat.
 * oji (おじ), meaning "uncle" (tentatively I reconstruct *wən-si, and the only Ryukyuan word I can find is Yoron fuja)
 * oba (おば), meaning "aunt" (tentatively I reconstruct *wəm-pa)
 * oiko (おいこ), meaning "nephew" (derived from earlier oi + -ko; tentatively I reconstruct *wə-pi)
 * meiko (めいこ), meaning "niece" (derived from earlier mei + -ko; tentatively I reconstruct *me-pi)
 * The above four terms also accept the pi- prefix to increase the generational gap (i.e. one prefix referring to great-uncles/great-aunts/etc.)
 * yauchi (やうち), meaning "family" (unreconstructible in Proto-Japonic, the Namari term is derived from ya- "house" + ochi "one's own group")

Verb conjugation
You may have noticed that I only gave stems for verbs in the above lists. This is because reconstruction of the Proto-Japonic verbal system is fraught with uncertainty. So far, I have made the following observations:
 * In general, there are vowel-stem (thematic) and consonant-stem (athematic) verbs. Most (but not all) thematic verb stems end in a diphthong.
 * Consonant-stem verbs add an epenthetic *-a- (which may alternate with *-ə-, but my evidence is flimsy) whenever a suffix beginning with a consonant is added (e.g. *kak- "to scratch; to write" becomes *kak-a-n- "not to scratch; not to write", with *-n- being the negation suffix; compare *ankay- "to rise" becoming *ankai-n- "not to rise").
 * The general infinitive suffix is *-i. This suffix may be elided after vowel stems ending in */i/ or a diphthong.
 * The general attributive suffix I reconstruct as *-ro. The */r/ is lost in consonant-stem verbs as a result of Whitman's Law. Some reconstruct an earlier *-rua, but in my opinion any differences can be explained by other factors (key word: can; I actually think the diphthongal realisation is highly likely, and may have originated from an earlier **-ruCa). My explanation for Western Old Japanese -u (as opposed to the expected -o in word-final position) is that attributives were syntactically adjectives in ancient Japanese, and thus phonologically bound to the following word.
 * The general imperative suffix I reconstruct as *-ryə, which becomes **-iə/**-ia → *-e for consonant stems. The glide explains the different forms between Western Japanese (-yo), Eastern Japanese (-ro) and Ryukyuan (-ru for dialects that retain the thematic-athematic distinction), as well as Proto-Japonic *-e for consonant stems (in conjunction with Whitman's Law).
 * Most Japonic languages have a participle/gerundive marked with -te (for Japanese) or -ti (for Ryukyuan), subject to euphonic changes (Irabu Miyako has lost the participle, and has replaced it with the infinitive, although traces of the participle can be found). This ultimately originates from Proto-Japonic *-tay, which attaches to the infinitive (e.g. *kak-i-tay "writing", *ankai-(i)-tay "rising").
 * Consistently, the most irregular verb in the Japonic languages is *kə- ("to come"). It is, as far as I know, the only verb whose stem does not end either in a consonant or a front vowel.
 * The general prohibitive suffix I reconstruct as *-ru-na. The */r/ is lost in consonant-stem verbs as a result of Whitman's Law. I am still investigating the link between the prohibitive and the attributive (note that I had the Namari prohibitive level with the attributive).
 * For Proto-Ryukyuan, I reconstruct the past tense marker *-tar-. A similar marker existed in Classical Japanese, but it represented the perfect. As such, I do not reconstruct tense for Proto-Japonic, but do reconstruct a perfect *-tar-.

Auxillaries I can reconstruct include: All of the above auxillaries attach to the participle.
 * *-ar- for the stative (from the inanimate existential)
 * *-wor- for the progressive (from the animate existential)
 * *-ək- for the preparative/prospective (from "to put")
 * *-mi- for the experiential (from "to see")

Derivative verb forms include: Both attach directly to the stem. In the case of consonant-stem verbs, the initial consonant of the suffix is lost.
 * *-sas- for the causative
 * *-raryay- for the passive

As of writing (2019-05-02), I have noticed a disagreement between two Wiktionary users regarding the proper form to use as the lemma for Proto-Japonic verbs. This is because the typical lemma for verbs in Japonic languages is the conclusive (only very early missionary dictionaries use the infinitive as the lemma), and the conclusive varies significantly between the Japonic languages (Japanese -u, Hachijō -u/-owa, Okinawan -(y)un, Yaeyama -un). In addition, I reconstruct a realis marker *-m(u) for Proto-Ryukyuan, which attaches to many (but not all) finite verb forms.

The general pattern I've found for conclusive forms is:
 * Japanese: -u, from Proto-Japanese *-u, which replaces the thematic vowel in most vowel-stems.
 * Northern Ryukyuan: *-i-wor-, derived from the combination of the infinitive with the animate existential. All languages also add the realis marker *-m(u).
 * Southern Ryukyuan (Sakishima): Unclear; may be a reflex of Proto-Japonic *-u, as evidenced in Irabu Miyako kafum ("to write", from a protoform *kakum(u)). Like with the Northern Ryukyuan languages, the realis marker *-m(u) is added (note that Ōgami Miyako has all but lost the indicative).

From the above, I can reconstruct Proto-Japonic *-u for the conclusive, based on evidence from Japanese and Miyako. However, I am unclear on how it interacts with vowel stems, as Japanese replaces the thematic vowel, Okinawan has since lost the thematic-athematic distinction (what were vowel stems have since fallen into the "clear" conjugational class along with r- and p-stems), and Irabu Miyako uses an infix -r-. It is indeed possible that the conclusive is actually *-ru, which would actually fit in with the forms of the attributive (**ruCa → *-rua → *-ro) and the prohibitive (*-ru-na) I have reconstructed. The */r/ would be lost in consonant-stem verbs in accordance with Whitman's Law. Additionally, the existential verbs *ar- and *wor- would not have any suffix in the conclusive, since preforms *ar-m(u) and *wor-m(u) would explain Okinawan &#39;an and wun respectively (their attributives are &#39;aru and wuru respectively, reflecting preforms *ar-ro and *wor-ro respectively).

Speaking of the existentials, they actually have derived forms. The inanimate existential *ar- may actually have a derived form *as- resembling a causative; this is the accepted etymology of the Miyako verb asïm/as ("to do"), and bears resemblance to other forms of "to do" in the other languages (which have generally been considered to have descended from *se-). Additionally, it has a derived form *ay- ("to get, to receive"), attested in Japanese (as -uru/eru) and Okinawan (as yīn). The animate existential *wor- has an inchoative form *woy- ("to sit"), which is attested in Japanese (as iru the animate existential) and Ryukyuan (e.g. Hateruma Yaeyama birun).

The issue of reconstructing *se- for "to do" is it does not follow the general pattern for verbs (which end either in a consonant or /i/). While *kə- ("to come") also does not follow the general pattern, it may have derived from an earlier **k-, especially if my hypothesis regarding *a/*ə alternation within verbs is correct (i.e. **k=ən- → *kə-n- "not to come" corresponds to *kak-an- "not to write" and **k=ryə → **k-yə → *kə "come!" corresponds to **kak=ryə → **kak-ya → *kak-e "write!"). The verb *se- has no such explanation with regards to its */e/. At least one person has suggested that it may have come from **si-a, with *-a- being the "imperfective" infix (e.g. **si-an- "not to do"), but I don't find his/her evidence convincing (there is no proof that historic Old Japanese ever distinguished between se1 and se2, and thus attempts to use the Middle Chinese pronunciations of man'yogana to determine the exact phonological shape are doomed to failure). Additionally, I've always seen *-a- as an epenthetic vowel, meaning it should not occur after a vowel or diphthong (since a consonant can directly follow them).

A more convincing argument comes from Miyako, which has the form as- instead of s-. This can be traced to a possible protoform *as-, which may have inflected as a regular consonant-stem verb. It is entirely possible that this was the original form of "to do", and that Japanese has innovated (I am unsure about Northern Ryukyuan, although I believe that *s- was inherited as-is; Hateruma Yaeyama sun "to do" is a regular class 1 verb reflecting a preform *s-). This is what I believe happened in Japanese:
 * Proto-Japonic *as- became *s-.
 * Forms such as *s-an- ("not to do") and *s-aryay- ("to be done") were initially retained, while **as=ryə ("do!") probably became *se. The infinitive remained *s-i and the conclusive developed via the path **as=ru → *as-u → *s-u.
 * The formation of the attributive and evidential was likely to have occurred after the loss of */a/, forming **s=rua → *suro and *s=ruay → *suray.
 * At some point, *-ryə was added to the imperative *se, forming *se-ryə (whence Classical Japanese seyo). While the causative *s-as- and the passive *s-aryay- remained unchanged, the negative was remodelled based on the imperative, becoming *se-n-. In the mean time, both *se and *se-ryə occurred in free variation.

For Namari, I have generally taken the verb forms of Japanese, although I have also taken the imperfective-perfective distinction found in Okinawan. In addition, I have innovated a future tense. With regards to the conclusive, I generally follow Japanese, although for monograde verbs I use -i instead of -ru (which would become *-yu).

With regard to consonant-stem verbs, the reconstruction of the conclusive as *-ru may be able to explain why there are only nine subclasses of consonant-stem verbs when thirteen are expected. So far, I have not seen any trace of d-stem, z-stem, y-stem or w-stem verbs in any Japonic language. I offer the following explanations:
 * The lack of y-stem verbs is simply a consequence of Proto-Japonic phonotactics; */j/ readily forms diphthongs when it follows a vowel, and in fact, the lack of y-stems is in my opinion the reason there is even a separate vowel-stem class in the first place. Therefore, especially considering that the vast majority of vowel-stem verbs end in */j/, I hypothesise that y-stem verbs and vowel-stem verbs are one and the same.
 * Similarly, a lack of w-stem verbs is a consequence of phonotactics, although in this case, the conjugations are realigned to form an r-stem verb. Although I only tentatively reconstruct one diphthong ending in */u/ (*/au̯/), it is possible that a number of modern r-stems, particularly those ending in -or- or -ur-, actually originated from Pre-Proto-Japonic w-stems. It will not be possible to determine if any -ur- verbs were originally w-stems, but some -or- stem verbs may originate from Pre-Proto-Japonic **-aw- verbs.
 * The lack of d-stem and z-stem verbs may be a consequence of assimilation. Hypothetical Pre-Proto-Japonic stems ending in **-nt- and **-ns- would have had conclusive forms in **-nt=ru and **-ns=ru respectively. While their non-nasalised counterparts **-t=ru and **-s=ru lost the */r/ due to Whitman's Law, it is possible that the fact that the coronals are nasalised (and thus voiced) resulted in rhotacisation of the coronal, via **-nt=ru → **-nd=ru → **-r=ru → *-r-u. This process would have also affected most n-stems as well, resulting in **-n=ru becoming **-r=ru. The n-stems that escaped this development are extremely rare, and I can only reconstruct one for Proto-Japonic (*sin- "to die"); it is notable that the two n-stem verbs in Classical Japanese are irregular (albeit conjugating identically to each other), showing forms that do not display the effects of Whitman's Law (e.g. shinuru instead of *shinu for the attributive).

Development of Japanese bigrade verbs
Unique to the Japanese branch(es) is the bigrade verb category; I have yet to find any such verb class in any Ryukyuan language. The bigrade class in Japanese alternates the thematic vowel between -e-/-i- and -u-, and in Western Old Japanese, the only regular class that distinguishes between the conclusive and attributive. In my opinion, this represents an innovation within Japanese, whereas the Ryukyuan languages kept the thematic vowel of vowel-stems invariant.

The bigrade class changes the thematic vowel to -u- in the conclusive (-u), attributive (-uru) and evidential (emphatic, -ure) base forms, while keeping the original thematic vowel in the imperfective (-e), infinitive (-e) and imperative (-e(yo)) base forms. Most likely, this was the situation in Proto-Japonic (using *-ay- verbs):
 * Infinitive: *-ay-i → *-ay
 * Conclusive: *-ai-ru
 * Attributive: **-ai-ruCa → *-ai-rua → *-ai-ruo
 * Emphatic: **-ai-ruCay → *-ai-ruay
 * Imperative: *-ai-ryə
 * Negative: *-ai-n-

In Pre-Proto-Japanese, I hypothesise the following forms:
 * Conclusive: *-ai-ru
 * Attributive: *-ai-ruo → *-a-uro
 * Emphatic: *-ai-ruay → *-a-uray

As you can see above, the attributive and emphatic forms underwent metathesis of the */u/ and */r/ (in the Ryukyuan languages, the */u/ was lost). By analogy with *se- (which by this point likely developed a conclusive *s-u), the conclusive evolved to *-u. Thus for Proto-Japanese:
 * Conclusive: *-ai-ru → **-a-u → *-u
 * Attributive: *-a-uro → *-uro
 * Emphatic: *-a-uray → *-uray

The loss of *-a- in the *-u- forms was likely conditioned by *se- and *kə- (both irregular and highly used verbs), whose conclusive, attributive and emphatic forms began with *su- and *ku- respectively. It is unlikely that the development of *-a-u- to *-u- (as opposed to monophthongisation into *-o- or retention of the diphthong into the separate dialects) was conditioned by thematics in *-uy- and *-oy-, as the vast majority of vowel stems were *-ay- stems. However, the existence of forms such as -o(1)ro(1) suggest that some dialects may have monophthongised the *-a-u- instead of dropping the */a/ (although this may instead be a scribal error).

The end result is that Western Old Japanese developed the following paradigm:
 * Infinitive: -e2
 * Conclusive: -u
 * Attributive: -uru
 * Emphatic: -ure(2)
 * Imperative: -e2yo2
 * Negative: -e2n-

For Eastern Old Japanese:
 * Infinitive: -e
 * Conclusive: -u
 * Attributive: *-uro1/*-o1ro1
 * Emphatic: -ure/*-o1re
 * Imperative: -ero2
 * Negative: -en-

And for completeness, here is Old Namari:
 * Infinitive: -e2
 * Conclusive: -u ← -o1
 * Attributive: -o1ro1
 * Emphatic: -o1re2
 * Imperative: -e2ro2
 * Negative: -e2n-

It should be noted that Japanese retained a monograde class; these likely originated from stems ending in the monophthong *-i- (such as *mi- "to see"). As far as I know, all monograde verbs in Old Japanese had monosyllabic stems, and it is likely that the strength of the vowel within this stem prevented it from being lost, instead causing */u/ to drop out, although an alternate hypothesis I will also put up is that plain i-stems (which would be represented in Western Old Japanese as stems ending in -i1-) represented an entirely different conjugational class from the upper bigrade stems, which developed from *-uy-, *-oy- and *-əy- stems (forming -i2-).

By the Early Middle Japanese period, the distinction between monograde and bigrade stems had blurred, with the consolidation of monosyllabic stems into the former and polysyllabic stems into the latter. This process, having already begun in the Old Japanese period, was likely conditioned by the merger of i1 and i2 into a single vowel /i/, and the more numerous lower vowel stems followed.

Japanese
Traditionally, Japanese verbs were described using six different base stems. In the modern language, two, the conclusive and the attributive, have all but merged, leaving five base stems, which are listed below for each conjugational class (alongside the participle): The participle in Modern Japanese has effectively become another base stem due to euphonic changes in quinquegrade (athematic) verbs. However, with a few exceptions (the most notable being iku becoming itte), they can be determined based on the final consonant of the stem alone. Thus, for most verbs, two principal parts (the conclusive/attributive and the imperative) are sufficient to describe their conjugation.

One thing to note, though, is that the Hachijō language distinguishes between the conclusive and attributive in consonant stems (they had merged in Classical Japanese), with the attributive being -o and the conclusive being -u or -owa (I am unsure of the etymology of the latter).

The tense-aspect system of Japanese is illustrated in the following table, using kaku ("to write") as an example:

Some dialects, such as those in Chūgoku and Shikoku, feature an additional aspect marked by adding oru to the infinitive (the auxillary morphs into yoru), giving forms such as kakiyoru (the reflex of the progressive in these dialects is kait(e)oru). This additional aspect form is cognate with the Northern Ryukyuan imperfective, and indeed in these dialects the -yoru form has an imperfective meaning (whereas the original progressive has morphed into a perfect/resultative). Unlike in the Northern Ryukyuan languages, however, the aorist present is still in use in these dialects.

It is important to note that the Japanese past tense does not exclusively refer to past events; it also takes the role of a perfect, making its meaning closer to that of the French passé composé rather than either the English past or perfect.

Japanese has the following derivative verb forms: Unlike in Okinawan, the polite form is only commonly used predicatively. None of these forms attach to verbal adjectives; the polite forms of adjectives simply attach desu to the end as if it were a particle.
 * Causative voice: -(s)aseru
 * Passive voice: -(r)areru
 * Potential voice: -eru for quinquegrade verbs, -rareru for other verbs
 * Polite form: -(i)masu

The verb suru is exceptional with respect to the formation of their voice forms:
 * Causative: saseru, not the expected *sesaseru
 * Passive: sareru, not the expected *serareru
 * Potential: dekiru, which is suppletive

Verbal adjectives conjugate differently in Japanese. Instead of ending in -u, they end in -i, and do not conjugate for aspect or voice. As such, there are only four finite forms (using takai "to be tall, to be high"): The general adverbial suffix is -ku.
 * Present affirmative taka-i
 * Past affirmative taka-katta
 * Present negative taka-ku-na-i
 * Past negative taka-ku-na-katta

The inanimate existential aru has a suppletive negative nai, which conjugates like any other verbal adjective (note, however, that Kansai dialects use the regular arahen). Neither the inanimate nor the animate existential iru (oru in Kansai dialects) conjugate for voice or aspect in Japanese, and not only does the copula lack aspect and voice conjugations, it is also defective, requiring analytical constructions for the imperative.

Okinawan
For this section I will refer to Loveless and his dissertation on the Okinawan language (1963). While over 55 years old, the fact that the Ryukyuan languages are moribund and primarily spoken by the elderly makes it still relevant. However, I have made some changes to conform to more modern practices regarding the language.

Okinawan has more conjugational classes than Japanese, despite the fact that it has lost the thematic-athematic distinction. It has twelve regular conjugational classes, all of which can be described using three principal parts (the conclusive, the participle and the imperative). Their respective forms are as follows:

The "clear" conjugational classes are classes 1, 3 and 5, and have the special property in that they have a special "truncated" stem, which entirely removes the verbal suffix (e.g. tu- from tuin). They and the "nasal clear" classes (2 and 4; I use the term "nasal clear" for etymological reasons) all originate from a combination of vowel-stems, r-stems and Proto-Japonic p-stems. Not listed above is the animate existential wun, which is irregular in one form only.

The verb &#39;yun ("to say") has a regular variant &#39;iyun, which conjugates like any other class 3 verb. The irregular variant is the only remnant of the Proto-Japonic p-stem verb category in conjugation (additional remnants can be found in derivation).

The verb chūn ("to come") bears some explaining. Like in Japanese, this verb is highly irregular. Selected forms, compared with those of kachun ("to write"), are listed below: Stem 1 of chūn has an irregular imperfective form, with a long /u/ instead of the short /u/ found in all other verbs (clear verbs may elide the /u/; I typically do this after /u/ and /i/, and remove the /ju/ entirely after long /e/). Stem 3, unlike all other verbs, is invariant, with the theme vowel of any attached suffixes being lost entirely (note that derivative verb forms add -r- to the stem; e.g. kūrasun "to be made to come"). Note that my reconstruction of the archaic attributive relies on Japanese evidence, as I am unsure of the status of the thematic-athematic distinction with respect to this form; the normal attributive is chūru. However, the prohibitive form kūnna may have arisen from an earlier *kūruna

Etymologically: With regards to Proto-Japonic p-stems, they have largely merged with the vowel-stems and r-stems. However, remnants of the p-stem category conjugations can be found in certain clear verb forms where -ā- is found when *-ara- is expected (e.g. warān "one does not laugh", from warayun "to laugh"), as well as their nominalisations, which have the form -ē as opposed to the infinitive -ai (the former comes from PJ *-api → PR *-awi, while the latter comes from *-ari). Loveless treated this as a morphophonemic phenomenon, but I interpret this as a retention of a separate conjugational class (which I will label 1a, for example).
 * Class 1 verbs are derived either from vowel-stems or r-stems that did not end in *-ir- in Proto-Ryukyuan. The example given, tuin, is cognate with Japanese toru.
 * Class 2 verbs are derived from vowel-stems or r-stems which had a preceding *-nu- or *-mu- in Proto-Ryukyuan. The example given, ninjun, is cognate with Japanese nemuru.
 * Class 3 verbs are derived from vowel stems that ended in *-i- in Proto-Ryukyuan. This */i/ induced progressive palatalisation, resulting in the participle form in /t͡ɕ/ instead of the expected /t/. The example given, chiyun, is cognate with Japanese kiru (monograde).
 * Class 4 verbs are derived from vowel-stems or r-stems which had a preceding *-ni- or *-mi- in Proto-Ryukyuan. Like above, the */i/ induced progressive palatalisation. The example given, nnjun, is cognate with Japanese miru.
 * Class 5 verbs are derived from r-stems that ended in *-ir- in Proto-Ryukyuan. Like the above two classes, the */i/ induced progressive palatalisation. The example given, chiyun, is cognate with Japanese kiru (quinquegrade).
 * Class 6 verbs are derived from t-stems. Progressive palatalisation occurred regardless, due to the presence of the infinitive marker *-i-. The example given, kachun, is cognate with Japanese katsu.
 * Class 7 verbs are derived from s-stems. Note the palatalisation in stem 1 (which has since been lost), and in stem 2 (similar to above). The example given, fusun, is cognate with Japanese hosu.
 * Class 8 verbs are derived from n-stems. I only know of one verb in this class, shinun, and it is cognate with Japanese shinu.
 * Class 9 verbs are derived from b-stems, and do not display any palatalisation. The example given, tubun, is cognate with Japanese tobu.
 * Class 10 verbs are derived from m-stems, and like b-stems do not display any palatalisation, with the occasional exception of stem 1 (which may change to -n-). The example given, kamun, is cognate with Japanese kamu ("to bite, to chew").
 * Class 11 verbs are derived from k-stems, and display palatalisation in both stems 1 and 2. The example given, kachun, is cognate with Japanese kaku.
 * Class 12 verbs are derived from g-stems, and like k-stems display palatalisation in both stems 1 and 2. The example given, tujun, is cognate with Japanese togu.

Anyway, the tense-aspect system in Okinawan is slightly different to that of Japanese. The negative is morphologically considered an "aspect", and as such, there are fewer negative forms than affirmative forms. Despite this, negatives of the perfect and progressive are possible, and are formed analytically (using -nēn and -wuran respectively combined with a topicalised form of the participle). The tense-aspect forms of kachun ("to write") are listed below:

The tense-aspect forms of wun (the animate existential) are listed below:

It is important to note that the word-final -n in all forms except the negative present is a marker of the conclusive (specifically, a realis or indicative marker; -sa marks what I call the subjunctive and -ssā marks indirect evidentiality, and there are other markers which I won't list here). It is omitted in some environments, and in the attributive and in kakari-musubi constructions replaced with the attributive ending -ru. Note that the negative present has identical conclusive and attributive forms.

Some verbs (namely, verbal adjectives, the inanimate existential and the copula) do not conjugate for aspect. Verbal adjectives form their negatives analytically, while &#39;an (the inanimate existential) has a suppletive negative nē(ra)n and the copula yan has the negative &#39;aran. However, apart from the lack of aspect, Okinawan stative and essive verbs conjugate identically to their non-defective counterparts (except with the lack of voice).

The derivative verb forms are listed below: Note that the polite form listed above does not co-occur with the perfect and progressive aspects. Instead, the infix -ibī- is added between the aspect marker and any following suffixes (e.g. kachōibītan "one was writing"). All stative and affirmative essive verbs take this infix as well (although note that yaibīn may become yēbīn in colloquial speech).
 * Causative: -asun (stem 3, class 7)
 * Passive/Potential: -arīn (stem 3, class 1i)
 * Polite: -abīn (stem 1, class 1)

While unlike in Japanese sun has a regular passive (sarīn), its causative is irregular (shimīn instead of *sasun). Some other verbs may also have irregular causatives and/or passives (e.g. the passive of nnjun "to see" is mīyun "to be seen" and the causative is mishīn "to show"). The verb sun is exceptional in that its passive is not used as a potential; instead nayun is used.

The negative essives, on the other hand, take the normal polite suffix, giving nēbiran and &#39;ayabiran.

There are two classes of verbal adjectives in Okinawan, although they are only distinguished in two forms (the nominalised form and the adverbial form) as a result of the depalatalisation of /ɕ/ before non-front vowels. The differences are listed below, using fī ("cold", class 1), taka ("high", class 1) and mijirashi ("unusual", class 2):