S. [ē], [ō] became [ī], [ū]; [ē|ō] > [ī|ū]

S. [ē], [ō] became [ī], [ū]; [ē|ō] > [ī|ū]

In both Sindarin and Noldorin, the long vowels [ē] and [ō] became [ī] and [ū]. Where [ē] and [ō] occur in Sindarin and Noldorin words, they are generally the result of the lengthening of short vowels in monosyllables. The same sound changes also occurred in the earliest versions of the language (Gnomish and Early Noldorin), and similar changes occurred in Welsh (WGCH/§59i), though in Welsh the sound change [ō] > [ū] only occurred in final syllables. Tolkien described these changes several times over his life:

ê gave î ... ô [gave] û (Gnome Vowels from the 1910s, PE15/13).
In the earliest recorded Noldorin, [ē, ǣ, ā, ǭ, ō] remained distinct though changed to [ī, ei, ǭ, ou, ū] (first version Tengewesta Qenderinwa [TQ1] from the 1930s, PE18/46).
In the earliest Noldorin ē, ę̄, ā, ǭ, ō appear as ī, ę̄, ǭ, ǭ, ū (second version Tengewesta Qenderinwa [TQ2] circa 1950, PE18/96).
C.E. ei, oi > [S.] ē > ī ... ō > ū (diphthong chart associated with Tolkien’s discussion of Hands, Fingers and Numerals from the late 1960s, VT48/7).

Examples are plentiful. Here are a few clear examples from each major period:

Conceptual Development: This seems to be an exceptionally stable and well documented phonetic rule, established very early and maintained thereafter. In Noldorin, however, it seems this change took place at a much more ancient stage than in Sindarin, in the Old Noldorin period before [ɣ] vanished. For example:

In the second example, if the ʒ [ɣ] vanished first, the result would have been [teɣē] > [tē] > [tī]. Likewise, this change took place before short [a], [o], [u] became [e], [œ], [y] preceding [i] in Noldorin, since there are several examples where the agental suffix -dîr (from ✶-ndēr) caused i-affection:

However, in Sindarin, suffixal -dir or -nir never causes i-affection:

The same is true of suffixal -hîr “lord” (from ✶-khēr):

Note that there are also Noldorin examples where i-affection does not occur, such as N. rhandir “wanderer” vs. S. randir “wanderer”. These Noldorin examples can be explained as late or reformed compounds, rebuilt from their constituent elements. In theory, the same might be true of the Sindarin compounds as well. But since i-affection occurs in no Sindarin examples, including those like dagnir and rochir that are likely ancient in origin, it is probably safer to assume that [ē] > [ī] simply occurred after i-affection in Sindarin.

As further evidence that the Sindarin sound change occurred well after the Old Sindarin period, in the 1960s Tolkien vacillated on the singular form of têw “letter” (< teŋwa), waffling between têw (PE17/44) and tîw (PE22/149). This vacillation makes sense if [ē] > [ī] occurred around same time that [ŋ] vanished with compensatory lengthening ([eŋ] > [ē]), and Tolkien couldn’t quite make up his mind which happened first. This makes the most sense if all these phonetic developments were part of the Sindarin rather than Old Sindarin period.

Hat tip to Elaran for pointing out the difference in i-affection between Noldorin and Sindarin in these cases.

Reference ✧ PE18/96

Order (01800)

After 01700 short [a], [o], [u] became [e], [œ], [y] preceding [i]
Before 02000 [ŋ] vanished with compensatory lengthening teñwa > tēwa > S. tēw PE17/44

Phonetic Rule Elements

[ē] > [ī] ✧ PE18/96 (ē > ī); PE19/91 (ē > ī)
[ō] > [ū] ✧ PE18/96 (ō > ū); PE19/91 (ō > ū)

Phonetic Rule Examples

dē > dī ē > ī > S. di ✧ PE17/95
dēra > dīra ē > ī dērā > S. dîr ✧ PE17/154
eðēwe > eðīwe ē > ī DEWE > S. edíw ✧ PE17/151
ēðe > īðe ē > ī Ezdē > S. Íð ✧ PE19/92
ēðe > īðe ē > ī ezdē > S. îdh ✧ PE19/91
ēðe > īðe ē > ī ezdē > S. îdh ✧ WJ/403
kēwa > kīwa ē > ī kēwā > S. cîw ✧ VT48/8
mēlambar > mīlambar ē > ī mēlā̆-mbar > S. milbar ✧ PE17/109
mēlambar > mīlambar ē > ī mēlā̆-mbar > mîl-mbar > S. milbar ✧ PE17/164
nēna > nīna ē > ī nēnā > S. nîn ✧ PE17/52
nēnatalma > nīnatalma ē > ī nēn-talma > S. nindalf ✧ PE17/167
nēθa > nīθa ē > ī nēthā > S. nîth ✧ VT47/14
rēða > rīða ē > ī reddā > rezdā > S. rîdh ✧ PE19/91
rēne > rīne ē > ī rēnē > S. rîn ✧ PM/372
-wē > -wī ē > ī > S. -wi ✧ PE17/189
xēru > xīru ē > ī kherū > S. hir ✧ Let/282
belekōre > belekūre ō > ū mbelek-óre > S. Belegûr ✧ PE17/115
drōv > drūv ō > ū D)ROB > S. drû ✧ PE17/99
dūme > dūme ō > ū dōmē > S. ✧ PE17/152
dūme > dūme ō > ū dōmē > S. ✧ SA/dú
gōle > gūle ō > ū ngōl- > S. gûl ✧ PE17/79
gōle > gūle ō > ū ngol- > S. gûl ✧ SA/gûl
gōle > gūle ō > ū NGOL > S. gûl ✧ WJ/383
gōrikova > gūrikova ō > ū gōr(i)kubā > S. gurgof ✧ PE22/155
l̥ōko > l̥ūko ō > ū (s)lōkō > S. lhûg ✧ PE17/160
lōθo > lūθo ō > ū loth > S. lúth ✧ PE17/161
onōre > onūre ō > ū NOR > S. onur ✧ PE17/168
oθθōia > oθθuia ō > ū otsōyā > S. othui ✧ VT42/25
r̥ō > r̥ū ō > ū SRON > srōn > S. rhû ✧ PE17/183
tindōmihelðe > tindūmihelðe ō > ū tindōmi-sel(dĕ) > tindúmhihel > S. Tinnúviel ✧ PE19/73
ōre > ūre ō > ū ʒorē > S. gûr ✧ VT41/11
xīθilōme > xīθilūme ō > ū χīþilōmē > hithlũṽ > S. Hithlũ ✧ PE17/133
xō > xū ō > ū > S. ✧ PE17/86

ON. [ē], [ō] became [ī], [ū]; [ē|ō] > [ī|ū]

References ✧ PE18/46; PE22/27

Order (01100)

After 00900 first in pair of voiced stops vocalized ᴹ✶negdē > N. nīdh EtyAC/NEG
Before 01200 [ɣ] vanished ᴹ✶teʒē > N. Ety/TEƷ
Before 04500 [j] vanished before [i], [ui] ᴹ✶at-yēn-ar > N. edinar Ety/YEN

Phonetic Rule Elements

[ē] > [ī] ✧ PE19/25 (ē > ī)
[ō] > [ū] ✧ PE19/25 (ō > ū)

Phonetic Rule Examples

andajēn > andajīn ē > ī ᴹ√YEN > N. ennin ✧ Ety/YEN
atjēnar > atjīnar ē > ī ᴹ✶at-yēn-ar > N. edinar ✧ Ety/YEN
dēn > dīn ē > ī ᴹ√DEN > N. dîn ✧ Ety/DEN
dēr > dīr ē > ī ᴹ√DER > ON. dîr ✧ Ety/DER
jēn > jīn ē > ī ᴹ√YEN > N. în ✧ Ety/YEN
jēnrinde > jīnrinde ē > ī ᴹ√YEN > iðrind > N. iðrin ✧ Ety/RIN
jēnrinde > jīnrinde ē > ī ᴹ✶ı̯en-rinde > N. îðrin ✧ Ety/YEN
jēre > jīre ē > ī ᴹ√YER > N. îr ✧ EtyAC/YER
kēn > kīn ē > ī ᴹ√KEN > cên > N. cîn ✧ EtyAC/KEN
kʰēril > kʰīril ē > ī ᴹ√KHER > ON. khíril ✧ Ety/KHER
lassepelēnē > lassepelīnē ē > ī ᴹ✶lassekwelēnē > N. lhasbelin ✧ EtyAC/KWEL
mēl > mīl ē > ī ᴹ√MEL > N. mîl ✧ Ety/MEL
nēdē > nīdē ē > ī ᴹ✶negdē > N. nīdh ✧ EtyAC/NEG
nēre > nīre ē > ī ᴹ✶neñrē > N. nîr ✧ EtyAC/NEI
nētʰē > nītʰē ē > ī ᴹ✶nēthē > N. nîth ✧ Ety/NETH
pantjēnare > pantjīnare ē > ī ᴹ√KWAT > N. penninar ✧ Ety/YEN
pelēnē > pelīnē ē > ī ᴹ✶kwelēnē > N. belin ✧ Ety/LAS¹
randēr > randīr ē > ī ᴹ√RAN > N. rhandir ✧ Ety/RAN
sēde > sīde ē > ī ᴹ√SED > N. sîdh ✧ Ety/SED
sparadēr > sparadīr ē > ī ᴹ√SPAR > N. feredir ✧ Ety/SPAR
tēɣ > tīɣ ē > ī ᴹ✶tēñe > N. ✧ Ety/TEÑ
tēra > tīra ē > ī ᴹ✶tēra > N. tîr ✧ Ety/TEƷ
trē > trī ē > ī ᴹ√TER > ON. trī ✧ Ety/TER
trēwā > trīwā ē > ī ᴹ✶terḗwā > N. trîw ✧ Ety/TER
tʰēa- > tʰīa- ē > ī ᴹ√THĒ > N. thio ✧ Ety/THĒ
tʰērē > tʰīrē ē > ī ᴹ✶thērē > N. thîr ✧ Ety/THĒ
xēro > xīro ē > ī ON. khēro > N. hîr ✧ Ety/KHER
arɣandōr > arɣandūr ō > ū ᴹ✶arʒā + ndōrē > arʒandōrǝ > ON. Arandur ✧ PE21/32
brōnā > brūnā ō > ū ᴹ✶b’rōnā > ON. brūna ✧ Ety/BORÓN
dō > dū ō > ū ᴹ√DOƷ/DÔ > N. ✧ Ety/DOƷ
dōlindē > dūlindē ō > ū ᴹ√DOƷ/DÔ > dúlind > N. dúlin(n) ✧ Ety/DOƷ
dōme > dūme ō > ū ᴹ✶dōmi > dūmh > N. ✧ SD/302
dōmilindē > dūmilindē ō > ū ᴹ✶dōmilindē > N. duilin ✧ SD/302
dōr > dūr ō > ū ᴹ√DOƷ/DÔ > N. dûr ✧ Ety/DOƷ
gorōmē > gorūmē ō > ū ᴹ✶Górōmē > N. Goru ✧ EtyAC/GÓROM
jōr > jūr ō > ū ᴹ√YOR > N. iûr ✧ EtyAC/YAR
kʰīsislōmē > kʰīsislūmē ō > ū ᴹ✶χīsi-slōmē > N. Cílu ✧ PE21/32
kʰōgore > kʰūgore ō > ū ᴹ✶Khōgore > N. Huor ✧ Ety/GOR
kʰōn > kʰūn ō > ū ᴹ√KHŌ-N > N. hûn ✧ Ety/KHŌ-N
kʰōpa > kʰūpa ō > ū ᴹ√KHOP > N. hûb ✧ Ety/KHOP
kʰōre > kʰūre ō > ū ᴹ√KHOR > N. hûr ✧ Ety/KHOR
kʰōtʰ > kʰūtʰ ō > ū ᴹ√KHOTH > N. hûd ✧ Ety/KHOTH
lōke > lūke ō > ū ᴹ√LOK > N. lhûg ✧ Ety/LOK
lōre > lūre ō > ū ᴹ√LOR > N. lhûr ✧ EtyAC/LOS
lōsien > lūsien ō > ū ᴹ√LOS > N. Lhuien ✧ Ety/LOS
mōl > mūl ō > ū ᴹ✶mōl- > N. mûl ✧ Ety/MŌ
mōta- > mūta- ō > ū ᴹ√ > N. mudo ✧ Ety/MŌ
ŋgōle > ŋgūle ō > ū ᴹ√ÑGOL > N. gûl ✧ Ety/ÑGOL
nōre > nūre ō > ū ᴹ√ > N. nûr ✧ Ety/NŌ
nōre > nūre ō > ū ᴹ√NŌ/ONO > ON. #nūre ✧ Ety/THEL
nōro > nūro ō > ū ᴹ√ > ON. #nūro ✧ Ety/NŌ
rōma > rūma ō > ū ᴹ√ROM > ON. rūma ✧ Ety/ROM
rōmena > rūmena ō > ū ᴹ√ > N. †rhufen ✧ Ety/RŌ
rōna > rūna ō > ū ON. rōna > N. rhûn ✧ Ety/RŌ
tindōme > tindūme ō > ū ᴹ√DOM > tindumh > tindu > N. tinnu ✧ Ety/TIN
tindōmiselde > tindūmiselde ō > ū ᴹ✶Tindōmiselde > ON. tindūmhiell ✧ Ety/TIN
ōle > ūle ō > ū ᴹ✶ñōle > N. ûl ✧ Ety/ÑOL
ōne > ūne ō > ū ᴹ✶ñōn- > N. ûn ✧ EtyAC/ÑŌ¹
ōno > ūno ō > ū ᴹ√ÑŌ²/ÑONO > N. ûn ✧ EtyAC/ÑŌ²
ōno > ūno ō > ū ᴹ√ONO > N. ûn ✧ Ety/ONO
wanōrō > wanūrō ō > ū ᴹ✶wa-nōrō > ON. wanūro ✧ Ety/TOR

G. [ē], [ō] became [ī], [ū]; [ē|ō] > [ī|ū]

HPG/§1.1

Order (01100)

Before 04900 [ll] became [l] lengthening preceding stressed vowel ᴱ✶oldō > G. ôla GL/62

Phonetic Rule Elements

[ē] > [ī] ✧ GG/14 (ē > ī); PE15/13 (ê > î; ê + r)
[ō] > [ū] ✧ GG/14 (ō > ū); PE15/13 (ô > û; ô + r)

Phonetic Rule Examples

gʷē > gʷī ē > ī ᴱ√u̯ē· > G. Gwî ✧ GL/45
gʷērī > gʷīrī ē > ī ᴱ√gu̯er > G. gwîri ✧ GL/46
gʷēs > gʷīs ē > ī #ᴱ√gwes- > G. gwîs ✧ GL/47
nēr > nīr ē > ī ᴱ✶nı̯ēr- > G. nîr¹ ✧ GL/60
tē > tī ē > ī ᴱ√ > G. ✧ GL/69
xēl > xīl ē > ī ᴱ√χele-k > G. hîl ✧ GL/49
gʷōri > gʷūri ō > ū ᴱ√GWORI > G. gur ✧ QL/104
ndōl > ndūl ō > ū ᴱ√ndolo- > G. dûl ✧ GL/30