S. [ī], [ū] often shortened in polysyllables; [ī|ū] > [ĭ|ŭ]

S. [ī], [ū] often shortened in polysyllables; [ī|ū] > [ĭ|ŭ]

Just as long vowels shortened before clusters, it seems that in both Sindarin and Noldorin the long vowels [ī], [ū] often shortened in polysyllables, as noted by David Salo (§4.166). Tolkien mentioned this phonetic development in his notes on the Noldorin usage of the Feanorian Alphabet from the 1930s:

... thus the ending au, ī, ū becoming thus unstressed was later reduced to o, i, u ... (PE22/31).

Lack of stress seems to be the main trigger for this sound change, and it mainly applied to long vowels in the final syllables of polysyllables (which were never stressed). The clearest examples are in Noldorin:

As the last two examples illustrate, since short [u] often became [o] in Sindarin and Noldorin, many examples of short [u] were originally long [ū] that had shortened. This is one of the ways [u] could survive in Noldorin, since in Old Noldorin long [ō] became [ū], and similarly for Old Sindarin. This is demonstrated in the clearest Sindarin example of the sound change [ū] > [u]: S. onur past tense of S. nor- “to run” (PE17/168): the u must have been from long [ū] because otherwise it would have become o. A similar shortening is seen in S. eniðen “*I meant to do it”, 1st sg. past tense of S. nidh- “to will, intend” (PE22/165). But this shortening is not seen in all past tenses: S. edíw past tense of S. dew- “to fail” (PE17/151).

The shortening sometimes happened even when [ī], [ū] were stressed, but these seem to be exceptions:

There are numerous examples of long vowels in stressed positions that were not shortened:

There are a few long vowels were preserved even in unstressed positions:

My best guess is that where it was part of a recognized element of a compound, the long vowel might have remain or been restored by analogy with the independent form. It’s unclear whether the vowel shortening applied to unstressed [ȳ], since we have no clear examples of this long vowel in an unstressed position. It was probably not mentioned in Tolkien’s original note above because long [ȳ] did not naturally arise in Noldorin, except as the lengthening of [y] in monosyllables (PE22/38). Given the comparative rarity of clear Sindarin examples, however, it’s possible that this vowel shortening was not a regular part of Sindarin phonetic development at all, even for [ī] and [ū], being only regular in Noldorin.

For a discussion of the possible shortening of [ǭ], see then entry on how [ǭ] became [au].

Phonetic Rule Elements

[ī] > [ĭ]
[ū] > [ŭ]

Phonetic Rule Examples

inīðen > iniðen ī > ĭ NID > S. eniðen ✧ PE22/165
rīθant > riθant ī > ĭ RIK > S. rithant ✧ PE17/167
onūr > onur ū > ŭ NOR > S. onur ✧ PE17/168

N. [ī], [ū] often shortened in polysyllables; [ī|ū] > [ĭ|ŭ]

§4.166 @@@

Reference ✧ PE22/31

Phonetic Rule Elements

[ī] > [ĭ]
[ū] > [ŭ]

Phonetic Rule Examples

edīnar > edinar ī > ĭ ᴹ✶at-yēn-ar > N. edinar ✧ Ety/YEN
endīn > endin ī > ĭ ᴹ√YEN > N. ennin ✧ Ety/YEN
feredīr > feredir ī > ĭ ᴹ√SPAR > N. feredir ✧ Ety/SPAR
feredīr > feredir ī > ĭ ᴹ√PHAR² > N. feredir ✧ EtyAC/PHAR²
iθīl > iθil ī > ĭ ᴹ✶Ithīl > N. Ithil ✧ SD/306
krīθa- > kriθa- ī > ĭ ᴹ✶k’rikta > N. critho ✧ Ety/KIRIK
nīniel > niniel ī > ĭ ᴹ✶neiniel- > N. niniel ✧ Ety/NEI
pelīn > pelin ī > ĭ ᴹ✶kwelēnē > N. belin ✧ Ety/LAS¹
pennīnar > penninar ī > ĭ ᴹ√KWAT > N. penninar ✧ Ety/YEN
r̥andīr > r̥andir ī > ĭ ᴹ√RAN > N. rhandir ✧ Ety/RAN
r̥īθa- > r̥iθa- ī > ĭ ᴹ√RIK(H) > N. rhitho ✧ Ety/RIK(H)
θīa- > θia- ī > ĭ ᴹ√THĒ > N. thio ✧ Ety/THĒ
gorūm > gorum ū > ŭ ᴹ✶Górōmē > N. Goru ✧ EtyAC/GÓROM
gwanūr > gwanur ū > ŭ ON. wanūro > N. gwanur ✧ Ety/NŌ
gwanūr > gwanur ū > ŭ ON. wanúre > N. gwanur ✧ Ety/THEL
gwanūr > gwanur ū > ŭ ON. wanūro > N. gwanur ✧ Ety/TOR
mūda- > muda- ū > ŭ ᴹ√ > N. mudo ✧ Ety/MŌ
r̥ūmen > r̥umen ū > ŭ ᴹ√ > N. †rhufen ✧ Ety/RŌ
tindūm > tindum ū > ŭ ᴹ√DOM > tindumh > tindu > N. tinnu ✧ Ety/TIN