Morphological Alternations in Nominal Stems

Short Monophthongs in Monosyllabic Stems

The stressed vowel in the initial syllable of monosyllabic stems, if it is a short monophthong, may undergo alternations due to various prehistoric developments in Goidelic phonology and morphology. These alternations can involve raising, lowering, or “diphthongisation”^[1] (via u-infection). The specific alternations depend on the vowel’s quality and the paradigmatic form.

Key Considerations:

Historical Form of the Root Vowel:

It is necessary to use the historical form of the root vowel as a reference point when applying these rules. Although raising and lowering might seem to be inverse processes, they are distinct due to differing restrictions and should be treated separately.
A root vowel can undergo either raising or lowering, but not both.
In masc o-stems, the voc.sg serves as a stable reference point, as it neither raises nor lowers. Relying on the nom.sg as a reference can be misleading, as it might give the false impression that raising is being improperly blocked.

Exceptional Forms:

Nouns borrowed from other languages (e.g., Latin) may not follow the expected phonological rules since they did not undergo the same prehistoric developments. These nouns are integrated into Goidelic morphology through analogy, which can lead to apparent rule violations.
Some Celtic forms also exhibit raising that seems to contradict their historical root vowel. This might be due to internal analogy. Regardless, once the reference point is established, raising or lowering should be viewed as one-way processes.

Raising and Lowering Processes:

Raising:

e → i; o → u
Blocked if followed by a voiceless consonant or a consonant cluster (except nasal + plosive clusters).

Lowering:

i → e; u → o
Blocked historically by -nd in words like find.

u-Infection:

Stressed Syllables:

a, e, i diphthongise into au, eu, iu.^[2]
- Blocked historically by geminated -ss- in words like mes.
- Exceptions: some inherited Celtic words (e.g., macc) and some borrowed words (e.g., salm) do not undergo u-infection.

Unstressed Syllables:

/ə/ is replaced by /u/.

Specific Declension Classes

Masculine o-Stems

The voc.sg contains the reference root vowel, which is neither raised nor lowered.
The gen and dat sg are raised, as well as the nom, acc, and voc pl.
All other forms are lowered.
The dat.sg is u-infected.
Only stressed a is u-infected in the acc and voc pl forms.^[3]

Neuter o-Stems

The gen and dat sg are raised.
All other forms are lowered.
The dat.sg is u-infected.

Chronological Background

The following chronological developments provide context for the vowel alternations discussed:

Unstressed long vowels shortened, except when followed by /h/.
Stressed interconsonantal /e/ and /o/ raised to /i/ and /u/ respectively when the following syllable had a high monophthong (/i, iː, u, uː/).
- Condition: The following consonant must be a voiced single consonant or a nasal + plosive cluster.
Stressed /ɑ/ altered to /ɑ^u/ when the following syllable contained /u, uː/.
Stressed and unstressed /e, i/ altered to /e^u, i^u/ when the following syllable contained /u/, but not /uː/.
- /sː/ in /esːu/ blocked diphthongisation of stressed /e/ but allowed it for unstressed /e, i/.
Stressed and unstressed /i, u/ lowered to /e, o/ when the following syllable had non-high back monophthongs (/ɑ, ɑː, o, oː/).
- /ɴd/ in /iɴdɑ/ blocked this lowering of /i/.
Final /h/ shifted to the following word or disappeared.
Final short vowels disappeared (apocope).
Final long vowels shortened.
Unstressed non-absolute-final monophthongs reduced in quality to /ə/, and unstressed non-absolute-final u-infected diphthongs became /u/.

Examples

nom.sg ball /bɑʟ/ ← /bɑʟɑ/ ← /bɑʟɑh/
dat.sg baull /bɑ^uʟ/ ← /bɑ^uʟu/ ← /bɑʟu/ ← /bɑʟuː/
acc.pl baullu /bɑ^uʟu/ ← /bɑ^uʟuː/ ← /bɑ^uʟuːh/ ← /bɑʟuːh/
nom.sg fer /f′er/ ← /werɑ/ ← /werɑh/ ← /wirɑh/
voc.sg fir /f′ir′/ ← /wire/
gen.sg fir /f′ir′/ ← /wiri/ ← /wiriː/
dat.sg fiur /f′i^ur/ ← /wi^uru/ ← /wiru/ ← /wiruː/
acc.pl firu /f′iru/ ← /wiruː/ ← /wiruːh/

Long Monophthongs in Monosyllabic Stems

o-Stems

Root vowels á, ó, ú, or í do not alter throughout the paradigm.
Root vowel é diphthongises^[4] to /eu/ when followed by a palatalised consonant and is written as éoi or éui.
- If é is preceded by a coronal, it diphthongises to /iu/ when followed by a palatalised consonant and written as íui.
When the following syllable contains u, or in the case of u-infection, é diphthongises to /eu/ and is written as éo or éu.
- If é is preceded by a coronal and followed by u, it diphthongises to /iu/ and is written as íu.

Notes

↑ The alternations to short stressed vowels affected by u-infection may not actually be diphthongs, but in accordance with convention and for the sake of simplicity, they will here be treated as such.
↑ There is only one known written example in an early manuscript where the o in nom.sg roth diphthongises into ou in dat.sg routh, but the u-infection of o generally does not appear to occur.
↑ The u-infection of other vowels in acc and voc pl forms, such as in euchu, is a Middle Irish development.
↑ Unlike the u-infection of short vowels, the diphthongisation of é had certainly resulted in actual diphthongs, hence the distinction with the long vowels /eu/ and /iu/ from the short vowels /a^u/, /e^u/ and /i^u/.

[1] The alternations to short stressed vowels affected by u-infection may not actually be diphthongs, but in accordance with convention and for the sake of simplicity, they will here be treated as such.

[2] There is only one known written example in an early manuscript where the o in nom.sg roth diphthongises into ou in dat.sg routh, but the u-infection of o generally does not appear to occur.

[3] The u-infection of other vowels in acc and voc pl forms, such as in euchu, is a Middle Irish development.

[4] Unlike the u-infection of short vowels, the diphthongisation of é had certainly resulted in actual diphthongs, hence the distinction with the long vowels /eu/ and /iu/ from the short vowels /a^u/, /e^u/ and /i^u/.

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Old Irish/Morphology

Cummal