Old Irish/Morphology

Stressed Short Monophthong Alterations in Nominal Roots

• Where raising occurs, e raises to i and o raises to u.
  • Raising is blocked if the vowel is followed by a voiceless consonant.
  • Raising is blocked if the vowel is followed by a consonant cluster, other than a nasal + plosive cluster.
• Where lowering occurs, i lowers to e and u lowers to o.
  • Lowering of i to e was historically blocked by -nd in find.
• Where u-infection occurs, stressed a, e, i and o may diphthongise into au, eu, iu and ou respectively.
  • Historically geminated -ss- blocked u-infection of stressed e in mes.
  • Exceptionally, macc does not experience u-infection.

Masculine o-Stems

1. The voc. sg. contains the reference root vowel. It is neither raised nor lowered.
2. The gen. sg., prep. sg., nom. pl., acc. pl. and voc. pl. are all raised.
3. All other forms are lowered.
4. The prep. sg. is u-infected.
5. Only stressed a is u-infected in the acc. and voc. pl.

Neuter o-Stems

1. The gen. and prep. sg. are raised.
2. All other forms are lowered.
3. The prep. sg. is u-infected.

Chronological Background

1. Unstressed long vowels were shortened, unless they were followed by /h/.
2. Stressed interconsonantal /e, o/ raised to /i, u/ respectively when the following syllable consisted of a high monophthong: /i, iː, u, uː/.
   1. The following consonant must only be a voiced single consonant or a nasal + plosive cluster.
3. Stressed /a/ was diphthongised to /au̯/ when the vowel in the following syllable consisted of /u, uː/.
4. Stressed and unstressed /e, i, o/ were diphthongised to /eu̯, iu̯, ou̯/ respectively when the vowel in the following syllable consisted of /u/, but not /uː/.
   1. The geminated /sː/ in /esːu/ blocked this diphthongisation of stressed /e/ but allowed it for unstressed /e, i/.
5. Stressed and unstressed /i, u/ lowered to /e, o/ respectively when the following syllable consisted of non-high back monophthongs: /a, aː, o, oː/.
   1. The /n̪ːd/ in /in̪ːda/ blocked this lowering of /i/.
6. Final /h/ shifted to the following word or disappeared altogether.
7. Final short vowels disappeared (apocope).
8. Final long vowels shortened.