Old Irish/Guide to Old Irish spelling

Consonants and marking lenition or lack of lenition

Old Irish orthography was based on Latin – as it was learnt by the Gaels from the Brythonic people – and British Latin pronunciation of that time had underwent basically the same processes as Welsh. The spelling is unintuitive to Modern Irish speakers, as it is based on Brythonic lenition patterns.

• The spelling of initial consonants is easy – since initial consonants weren’t generally lenited (except for grammatical initial mutations), they are read as generally expected in Latin-based writing systems, initial b, d, g, p, t, c and m denote /b, d, ɡ, p, t, k, m/ respectively.
• Irish lenition of voiceless /p, t, k/ is marked, as today, by h after them – ph, th, ch mean /ɸ, θ, x/ respectivaly: ‘her cat’ is a catt /a ˈkat/ but ‘his cat’ is a chatt /a ˈxat/.
• The consonants between vowels (and liquids like n, r, l, and in coda after a vowel) are to be read as if they were lenited in Welsh, that means:

• b, d, g, m in the middle of a word are just lenited to /β, ð, ɣ, β̃/: the word rígain ‘queen’ is read /r´iːɣən´/, g between vowels denotes lenited /ɣ/ – hence modern Irish banríon, pre-reform (ban)ríoghan,
• p, t, c are voiced /b, d, ɡ/: the word póc is read /poːɡ/ and gives modern póg,
• medial /m/ and voiceless /p, t, k/ are often written doubled, so lomm /lom/ ‘bare, naked, exact’, peccad /p´ekəð/ ‘sin’, macc /mak/ for ‘son’, catt /kat/ for ‘cat’, etc. – but this is hardly consistent, often it’s ambiguous if some final or medial c means /ɡ/ or /k/ (and it’s more consistent in the middle of the word than word-finally), for example the word for ‘small’ is often written as becc with double cc even though it’s to be red /b´eɡ/ (modern beag).

Note: there is no way to mark lenition of initial voiced /b, d, ɡ, m/ – ‘his mother’ ⁊ ‘her mother’ are generally both a máth(a)ir – it’s either /a ˈmaːθər´/ or /a ˈβ̃aːθər´/ depending on meaning. But lenition of voiceless stops is marked consistently. And we know the voiced ones were lenited in the same positions from metrical clues (alliteration, rhyming, etc.).

The doubled non-lenited mm, ll, rr, nn are sometimes also written initially after unstressed words (like a ‘his, her’), so a mmáthair is unambiguously /a ˈmaːθər´/ ‘her/their mother’ (but can be written a máthair too) – spelt as if it were a single word.

Lenited s and f are often written ṡ /h/, ḟ (no sound). The s from old *sw can also be lenited to /ɸ/ written variously as f, ph, ṡ (so a fiur, a phiur, a ṡiur for /a ˈɸi.ur/ ‘his sister’, from siur, siür /s´i.ur/).

These conventions are imo nicely presented by two forms of the name Patrick to be found in Old Irish – it was borrowed twice from Latin Patricius:

• first is the older Cothriche, Cothrige /koθ´r´əɣ´e/, which continues something like [kʷaθrixijah] (phonemically /kʷatrikijas/, which would be written something like *qat(t)ric(c)ias in ogham) – the Gaels borrowed Latin /p/ as /kʷ/ as there was no native /p/ phoneme in Primitive Irish, and the medial voiceless /t, k/ were lenited to /θ, x/, the nominative ending /-ah/ fell out due to apocope before Old Irish,
• later Pátraic /paːdrəɡ´/ – notice t and c written like in Latin original but read voiced – that’s because it was borrowed in later times from British Latin with the Brythonic lenition, and this form is continued today in Irish Pádraig and Scottish Gaelic Pàdraig.