OS. [j] became [i] after vowels; [VjV|-Vj] > [ViV|-Vi]

OS. [j] became [i] after vowels; [VjV|-Vj] > [ViV|-Vi]

It is well known that non-initial y ([j]) became vocalic [i] in both Sindarin and Noldorin. This is reflected in its spelling system, where i represented a vowel in the middle of words, but y at the beginning of words:

I initially before another vowel has the consonantal sound of y in you, yore in Sindarin only: as in Ioreth, Iarwain (LotR/1114).

This shift of [j] to [i] took place in two phases (or three phases if you include Primitive Elvish developments: see below). First, any y appearing between vowels became i ([VjV] > [ViV]), and later any remaining non-initial y became i ([CjV] > [CiV]). This the timing of two phases is most obvious from Old Noldorin examples. Compare:

Versus:

The only attested example of intervocalic y in Old Noldorin is Phayanṓr (N. Feanor), and this probably represents an older form. Also note that there would be no examples of pre-consonantal y [VjC] in Old Noldorin or Old Sindarin, since these had already become i in Primitive Elvish, and in fact were the main source of primitive i-diphthongs: [VjC] > [ViC]; this primitive sound change makes for “three phases” of y becoming i, as mentioned above.

The picture is less clear in Sindarin, but there is indirect evidence that intervocalic y became i in Old Sindarin, because of how the resulting diphthongs developed. In particular, the resulting i-diphthongs underwent the same development as original primitive i-diphthongs, indicating an early phonetic change. For example:

This indicates the change of [VjV] > [ViV] probably occurred at an ancient stage, since otherwise the resulting [ai] diphthong would have survived. Diphthongal developments in Noldorin also support such an ancient change, such as: ᴹ√GÁYAS > ON. gaia > N. gae “dread” and not **gai or **gei.

Finally, there is one Old Noldorin example that indicates that the sound change [-Vj] > [-Vi] (final y after a vowel becoming i) occurred only in Old Noldorin, and not in Primitive Elvish:

Here the final indeterminate vowel [ǝ] (probably originally short [ă]) was lost primitively, but the result was not a primitive diphthong [āi] > [ai], which would have become [ae] or [oe] in Noldorin. Instead, it seems that the long [ā] became [ǭ], and then the resulting diphthong [ǭi] ultimately became [oi] > [ui]. This is only possible if the final [j] was preserved long enough for these Noldorin-only phonetic developments to occur.

It isn’t clear whether this preservation of primitive final [j] after a vowel applied to (Old) Sindarin’s phonetic history, but for now I am assuming it does until contrary evidence appears.

Order (02600)

Before 02800 [oi], [ǭi] became [ui], [oi] gāyā > S. goe PM/363

Phonetic Rule Elements

[VjV] > [ViV]
[-Vj] > [-Vi]

Phonetic Rule Examples

aθaja > aθaia VjV > ViV aþayā > S. athae ✧ PE17/49
glossōja > glossoia VjV > ViV LOS > S. glosui ✧ PE17/161
gǭja > gǭia VjV > ViV gāyā > S. goe ✧ PM/363
jujal > juial VjV > ViV yuy(u)ŋal > S. uial ✧ PE17/169
kasraja > kasraia VjV > ViV cas-raya > S. cathrae ✧ VT42/12
-ōja > -oia VjV > ViV ō-yā > S. -ui ✧ VT42/25
r̥aja > r̥aia VjV > ViV SRA/SRAYA > S. rhae ✧ PE17/172
sarnije > sarnīe VjV > ViV sarniye > S. Serni ✧ VT42/11
sɸanǭja > sɸanǭia VjV > ViV SPAN > S. fanui ✧ PE17/36
-ūja > -uia VjV > ViV ū-yā > S. -ui ✧ VT42/25
uruja > uruia VjV > ViV ur- > S. Urui ✧ SA/ur
waja > waia VjV > ViV WAYA > S. gwae ✧ PE17/33
waja > waia VjV > ViV WAYA > S. Gwae ✧ PE17/189
wǭja > wǭia VjV > ViV wāyā > gwoe > S. gwae ✧ PE17/34
ɸanǭja > ɸanǭia VjV > ViV FAN > S. fanui ✧ PE17/26
ɸereja > ɸereiā VjV > ViV PHERE > S. ferui ✧ PE17/181

ON. [j] became [i] after vowels; [VjV|-Vj] > [ViV|-Vi]

GS/§4.32 WGCH/§100i-2 [usually remained in Welsh between vowels] @@@ after diphthong changes but before oi > ui

Order (03100)

Before 03400 [oi], [ǭi] became [ui] ᴹ✶wāyā > wōia > ON. uia Ety/WAY
Before 04600 [w] vanished before [u] ᴹ✶wāyā > wōia > ON. uia Ety/WAY

Related

Phonetic Rule Elements

[VjV] > [ViV]
[-Vj] > [-Vi]

Phonetic Rule Examples

mbǭj > mbǭi -Vj > -Vi ᴹ✶mauy- > N. bui ✧ Ety/MBAW
nǭj > nǭi -Vj > -Vi ᴹ✶nāyǝ > noi > ON. nui ✧ Ety/NAY
ajar > aiar VjV > ViV ᴹ√ÁYAR > N. oear ✧ Ety/AY
būja- > buia- VjV > ViV ᴹ✶beuyā́- > ON. buióbe ✧ Ety/BEW
gaja > gaia VjV > ViV ᴹ√GÁYAS > ON. gaia ✧ Ety/GÁYAS
istǭja > istǭia VjV > ViV ᴹ✶istāyā > N. istui ✧ Ety/IS
jūjo > juio VjV > ViV ᴹ√ > N. ui- ✧ Ety/YŪ
pūja- > puia- VjV > ViV ᴹ√PIW > ON. puióbe ✧ Ety/PIW
pʰūja- > pʰuia- VjV > ViV ᴹ√PHEW > ON. phuióbe ✧ Ety/PHEW
tūja- > tuia- VjV > ViV ᴹ√TIW > ON. tuio- ✧ Ety/TIW
tʰūja- > tʰuia- VjV > ViV ᴹ√THŪ > N. thuio ✧ Ety/THŪ
wǭja > wǭia VjV > ViV ᴹ✶wāyā > wōia > ON. uia ✧ Ety/WAY
wǭjar > wǭiar VjV > ViV ᴹ✶wā́yārō̆/Vā́yārō̆ > N. Uiar ✧ Ety/WAY
ɸajanǭr > ɸaianǭr VjV > ViV ON. Phayanṓr > Feanoúr > N. Féanor ✧ Ety/PHAY

ᴱN. [j] became [i] after a vowel; [ij] > [ī]

Phonetic Rule Elements

[ij] > [ī] ✧ PE15/64 (iı̯ > ī)