Revisiting Old Irish: The sounds

The first tough bit of Old Irish is the spelling system and phonology.

There are two issues here, for the native speaker of English

  1. Old Irish uses phonemic contrasts that we don’t (particularly palatalisation)
  2. The Old Irish spelling system doesn’t reflect its phonology in a couple of important places.


Old Irish uses 17 or 18 letters (five vowels and 11 or 12 consonants, depending on how you count <h>): <a>, <b>, <c>, <d>, <e>, <f>, <g>, <h>, <i>, <l>, <m>, <n>, <o>, <p>, <r>, <s>, <t>, <u>.

The “additional” letters in Modern English (i.e. the ones that are “missing” in Old Irish) are <j>, <k>, <q>, <v>, <w>, <x>, <y>, and <z>. This is actually a pretty common set of “missing” letters for medieval languages: <j> is often a graphic variant for <i>, <v> is often a graphic variant for <u>, and <w> can be spelled <uu> (i.e. a “double u”). <k>, <q>, and <x> can be spelled using other letters. And <z> is just not that common a sound.

<h> is an odd case in Old Irish. There is apparently some evidence it may have been pronounced in certain contexts, but it was not consistently represented in these contexts by scribes. Elsewhere it is used with (originally) with the letters <c>, <t>, and <p> (I.e. the spelling of the voiceless stops /k/, /t/, and /p/) to indicate “lenition” or the conversion of a stop to a fricative: <ch> spells /x/ (broad) or /ç/ (slender), <th> spells /θ/, and <ph> spells /ɸ/ (i.e. a voiceless bilabial fricative). <h> is also added in front of vowels in “small” words for non-linguistic reasons. In such cases it is not pronounced.

In addition to these letters, Old Irish manuscripts also some diacritics: an acute accent (known as fada or “long” in Irish) and a punctum delens or dot above a letter. The fada marks long vowels; the punctum delens a letter that is silent (the punctum delens was also used by scribes to indicate a mistaken letter that needs to be deleted from a word or text, though in my experience it is usually under the letter in such cases).

Finally, Old Irish also uses <i> and <a> sometimes to indicate whether a preceding or following consonant is “broad” or “slender” (i.e. palatized). So cele is sometimes spelled ceile to indicate that the l is palatised.


Vowels and diphthongs

Old Irish vowels have their “continental” value—which is also the value they had before the Great Vowel Shift in English: /i(ː)/, /e(ː)/, /a(ː)/, /o(ː)/, /u(ː)/

There are eight different diphthongs, which are spelled using eleven different combinations of letters:

Spelling Sound
<íu(i)> /io/
<ía(a)> /ia/
<éo(i)>, <éu> /eɔ/
<áu> /aU/
<áe>, <aí> /aɪ/
<óe>, <oí> /oɪ/
<úa(i)> /iU/
<uí> /ui/ ?

As noted above, in some cases, what look like diphthongs are really diacritics.


Palatalisation (broad vs. slender consonants)

All Old Irish consonants except /h/ have “broad” and “slender” (i.e. palatised) equivalents. Consonants are slender:

  1. if they are followed in the same word by a <e> or <i>
  2. if they are final and preceded by a <i>

Otherwise they are broad.

Spelling Broad value Slender (palatised) value
<b> b
<c> k
<d> d
<f> f
<g> g
<l> L
<m> m
<n> N
<p> p
<r> R
<s> s
<t> t

The precise values of broad L, N, and R are not known. It is thought that they were tense.


In addition to broad and slender values, Old Irish consonant spellings have different values depending on their position in the word and phonological mutations caused by the surrounding context. As a rule, the sounds vary by position (initial vs. medial vs. (sometimes) final). They can also be influenced by preceding words and syllables and following syllables.

This means that for each broad and slender version of each letter, you need to keep track of as many as five relevant phonemes: the initial unmutated sound, the initial lenited sound, the initial eclipsed sound, the normal medial and final sound and the doubled medial and final sound.

Here’s a table with my understanding of this:

Initial sounds
Medial and final sounds
Voiced Stops (and <m>) <b> /b/ Nasal /m/ (spelled <mb>) Voiced fricatives /v/ Voiced fricatives /v/
<d> /d/ /N/ /ð/ /ð/
<g> /g/ /ŋ/ (spelled <ng>) /γ/ /γ/
<m> /m/ /m/ /ṽ/ /ṽ/
Voiceless Stops <c> /k/ Voiced Stops /g/ Voiceless fricatives /x/ Voiced Stops /g/
<t> /t/ /d/ /ϴ/ /d/
<p> /p/ /b/ /f/ /b/
Voiceless Fricative <f> /f/ Voiced fricative /v/ Reduced Ø (spelled <ḟ>) Voiceless Fricative /f/
Voiceless spirant <s> /s/ Voiceless spirant /s/ /h/ (spelled <ṡ>) Voiceless spirant /s/
(Tense) Liquids <l> /L/ (Tense) Liquids /L/ Lax /l/ Lax /l/
<n> /N/ /N/ /n/ /n/
<r> /R/ /R/ /n/ /r/


Old Irish has a strong stress on the first syllable of nouns, adjectives, and non-finite verbs.


The material in this blog is adapted from two main sources: Tigges and Ó Béarra, An Old Irish Primer and “Dennis King, [“Old-Irish Spelling and Pronunciation.]. Here are some other sources used.

“Lenition.” 2014. Wikipedia, the Free Encyclopedia.

“Old Irish.” 2014. Wikipedia, the Free Encyclopedia.

“Old-Irish Spelling and Pronunciation.” 2014. Accessed February 13.

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