Old Irish was affected by a series of phonological changes that radically altered its appearance compared with Proto-Celtic and older Celtic languages (such as Gaulish, which still had the appearance of typical early Indo-European languages such as Latin or Ancient Greek). The changes occurred at a fairly rapid pace between 350 and 550 CE.
A capsule summary of the most important changes is (in approximate order):
They led to the following effects:
In more detail, syncope of internal syllables involved the following steps (in approximate order):
All five Proto-Celtic short vowels (, , , , ) survived into Primitive Irish more or less unchanged in stressed syllables.
During approximately A.D. 450-550 (just before the Old Irish period, c. 600-900), however, there occurred several vowel-changes (umlauts). Former vowels are modified in various ways depending on the following vowels (or sometimes surrounding consonants). The mutations are known in Celtic literature as affections or infections such as these, the most important ones:
Nominal examples (reconstructed forms are Primitive Irish unless otherwise indicated):
Before i-affection occurred, there was also a lowering of initial-syllable Proto-Celtic e to a before palatalized reflexes of , unless a followed them in the next syllable in Primitive Irish (no matter the 's origin) which would instead lead to i-affection to i. For instance, Proto-Celtic "(s)he lies" vs. "they lie" vs. "lying" led to a three-way split in Old Irish , , and respectively.
Verbal paradigm example:
The result of -affection and -affection is that it is often impossible to distinguish whether the root vowel was originally or ( < and < have identical declensions). However, note the cases of vs. above for which -affection, but not -affection, was blocked by an intervening .
The result of u-infection of *a eventually reduced to /u/ during the Old Irish period. It does not share its later evolution with original *au, which instead became (or broken into ) in Old Irish.
In addition, the u-affection of a when the u preceded a palatalized consonant originally turned the a into an , whose spelling varied among au, ai, i, e, and u depending on the scribe. then spread to various terms prefixed with "fore-" and "ad-".
Stressed short front vowels in hiatus underwent a loop throughout Primitive Irish and early Old Irish in which they would repeatedly switch between i and e. McCone outlines the loop as follows:
Examples of words that went through this loop include:
Proto-Celtic *a before nasals followed by a stop manifested as the allophone in the prehistory of Irish.
Short vowels and *e, and *i regularly became e before nasals followed by originally voiceless stops, which then lengthened to in stressed syllables.
But a different development of occurred before nasals followed by voiced stops. According to Schrijver, this became i when affected by i-affection and a when it was not. McCone however instead believes that i was the default outcome of before voiced nasals unless a-affection applied, lowering it down to a. Some examples of these developments include:
Additionally, and *e were also raised to i when followed by a nasal, a voiced stop, and then either *e or a word-final *a followed by a nasal, despite those vowels not triggering i-affection.
In Primitive Irish, *a and *i were rounded to o and u respectively when preceded by Celtic labiovelars and or a consonant cluster containing them. The rounding of *i also required the following consonant to be palatalised. This rounding occurred after i-affection as "prays" (< ) faced rounding even though the rounded vowel was originally an *e. Since "buys" (< ) faced no rounding even though its stressed vowel was originally an *i, the rounding may also have taken place after a-affection as well, but Schrijver does not find the evidence for that to be reliable.
Examples of this rounding process include:
Original *a preceded by a labiovelar consonant and followed by *n and an originally voiceless stop was rounded and then broken into Old Irish .
After a-affection occurred in Primitive Irish, dental and velar fricatives were dropped when immediately preceding a sonorant consonant, but transformed the preceding vowel into a long vowel or a diphthong. This development affected both stressed and unstressed syllables.
Proto-Celtic long vowels and diphthongs develop in stressed syllables as follows:
The Old Irish diphthongs , , stem from earlier sequences of short vowels separated by *, e.g. "druid" < "tree-knower".
Most instances of and in nonarchaic Old Irish are due to compensatory lengthening of short vowels before lost consonants or to the merging of two short vowels in hiatus: 'hundred' < Proto-Celtic (cf. Welsh ) < PIE .
See Proto-Celtic for various changes that occurred in all the Celtic languages, but these are the most important:
From Proto-Celtic to Old Irish, the most important changes are these:
In the onsets of stressed syllables, Proto-Celtic stops, *m, and *s were preserved. On the other hand, *y and were always lost. But in other situations, inherited consonants often mutated into different consonants entirely. The two major mutations are lenition and nasalization. These mutations not only operated between word boundaries (as a synchronic grammatical process well-known in Insular Celtic languages) but also word-internally.
When lenition applied, stop consonants and /m/ became fricatives. Lenition applied to a consonant when it was either between two vowels, or in syllable codas immediately after a vowel. The lenition mutations did not all arise in one wave of sound change; instead, there were three phases of lenition.
On the other hand, nasalization of a consonant was triggered by following a nasal consonant.
This mutation gave rise to the eclipsis mutation in modern Irish.
Below is a table of basic Old Irish reflexes of Proto-Celtic consonants, including unmutated and mutated outcomes.
Old Irish preserves, intact, most initial clusters unlike many other Indo-European languages.
Preserved initial clusters:
Modified initial clusters:
The palatalized consonants arose in multiple stages. In theories of palatalization, the front vowels are Proto-Celtic e, ÃÂ, i and ë.
The first palatalization affected single consonants and sequences of a nasal consonant followed by a homorganic voiced stop. The palatalization depended on not only the vowel after the consonant, but also the vowel before the consonant. The following Proto-Celtic vowel setups were eligible for the first palatalization:
The first palatalization must have occurred before a-affection, because otherwise the presence of palatalization of the genitive singular of ÃÂ-stems (ending in *-iyÃÂs > *-iyÃÂh > *-eyÃÂh > -e) would be dependent on root shape, yet only nigh-inevitable palatalization is actually attested in such forms.
Demonstrations of the first palatalization include:
After the first palatalization, another palatalization ensued. Final-syllable Primitive Irish front vowels, after merging into a "palatal schwa", forced the palatalization of any consonants preceding them except the consonant cluster cht , which could never be palatalized. Greene labels this stage the second palatalization, while McCone treats this as a substage of the first palatalization.
The third palatalization entailed any front vowel in a second or fourth syllable of a Primitive Irish word causing the palatalization of the preceding consonants. Like with the final-syllable palatalization, these front vowels were generally assumed to merge into a palatalizing schwa before causing palatalization.
The following Primitive Irish vowels merged into the palatalizing schwa in second or fourth non-final syllables:
Other vowels were reduced to non-palatalizing schwas. After syncope regularly removed these vowels, the palatalization (or lack thereof) tended to spread across the resulting consonant cluster.
However, if syncope results in a sonorant becoming surrounded by a consonant before it and a consonant after it, the effects of the third palatalization (or lack thereof) are often overridden by a special set of sound laws, presumed to be caused by the stranded sonorant assuming the role of syllable nucleus until epenthesis occurs before the sonorant.
Lenited fricatives and straddling the boundary between a stressed syllable and an unstressed one tend to disappear if there is a homorganic consonant near the end of the next syllable. If a non-front vowel comes into contact with a front vowel after it due to this deletion, the two vowels fuse into a diphthong like or . Otherwise a hiatus between the two vowels may be formed instead.
For the purposes of this sound law, is treated as if homorganic with s, due to its general origin in lenitions of Proto-Celtic *s.
Some examples of this sound law are given below:
This deletion and diphthong formation happened before syncope. As a demonstration, ended up syncopating its etymon's third syllable instead of the usual second. This can be explained by the first and second syllables fusing into one syllable due to dissimilatory deletion, making the etymon's third syllable the second syllable at the time of syncope.
Many intervocalic clusters are reduced, becoming either a geminate consonant or a simple consonant with compensatory lengthening of the previous vowel. During the Old Irish period, geminates are reduced to simple consonants, occurring earliest when adjacent to a consonant. By the end of the Old Irish period, written are repurposed to indicate the non-lenited sounds when occurring after a vowel and not before a consonant.
Cluster reduction involving :
Cluster reduction involving :
Lenited stops generally disappear before sonorants , with compensatory lengthening of the preceding vowel. Many examples occur in reduplicated preterites or words with consonant-final prefixes (such as ):
However, , , survive: "he perforates" < PCelt ; "goat" < PCelt (cf. Welsh ); "shame" < PCelt (cf. Welsh ).
Any /h/ that ends up in an intervocalic consonant cluster for any reason triggers the devoicing of adjacent consonants in the cluster.
Sequences of in Primitive Irish are reduced to simple *-ss- if the vowel preceding the sequence is unstressed.
Proto-Celtic *w had a complex series of outcomes in Old Irish.
MacNeill's law refers to a sound law before and during the Old Irish period causing the loss of lenition of n and l in final unstressed syllables even though they are etymologically expected to be lenited in that position. Newly word-final n and l became unlenited nn and ll when the unstressed syllables containing them began in r, n, l, , or . A vowel between the trigger consonant and the affected l or n must also be present for the law to apply. However, MacNeill's law often failed to apply if this vowel had been inserted by anaptyxis in the first place instead of coming from an earlier Proto-Celtic vowel.
Proto-Celtic final syllables were often reduced or deleted by Old Irish times.
Unstressed Proto-Celtic -es- became -is- early on if immediately followed by a vowel. The resulting -is- triggers i-affection on preceding stressed syllables as it evolved into *-ih- and then *-iy- in Primitive Irish before either remaining as -i or undergoing a-affection to -e by Old Irish. This raising of *-es- occurred before the early deletion of final *-i. McCone lists the following examples of this raising:
The absolute-conjunct distinction in Old Irish non-prefixed verbs is generally explained via the apocope of final *-i in multiple Indo-European primary person-number endings that ended in *-i. This normally happens in the conjunct forms, while in the absolute forms the apocope was blocked due to a succeeding enclitic element. Contrast:
The identification of the enclitic that was used to create Old Irish's absolute verb forms has been subject to controversy. At first, Warren Cowgill and Frederik Kortlandt supposed that the protective enclitic was a particle derived from "is". The current mainstream explanation, pioneered by Peter Schrijver in the 1990s, identifies this particle as derived from "beyond", cognate to Latin "and". Kim McCone on the other hand refuses to identify any specific particle responsible.
The environment of final i-deletion is also controversial. McCone believes that all final *-i was lost by default, while Schrijver limits the apocope to just after *t, *s and also *k.
After the lenition of post-vocalic consonants in unstressed syllables and the apocope of -i, an early Primitive Irish syncope occurred to vowels between two dental fricatives or two rhotics in final unstressed syllables preceded by another unstressed syllable. For dental fricatives, the result of their collision due to the syncope was originally but would then become due to a later voicing in the same environment as the syncope. On the other hand, collision of two rhotics over this syncope would result in unlenited rhotic rr. Unlike the main early Irish syncope, this syncope could never palatalise the resulting consonant produced by the collision of involved continuants, no matter what vowel was between them. Instances of this syncope include:
McCone envisions the evolution of final syllables across Primitive Irish into Old Irish as follows.
Proto-Celtic unstressed long vowels were shortened unless protected by a following Primitive Irish final *-h, whether that *-h came from a final -s (as in several nominal inflectional endings) or -ti (as in 3rd-person singular present forms of verbs). These shortened long vowels included the feminine ÃÂ-stem nominative singular ending *-àand the masculine and neuter o-stem ending *-ë.
Then, absolutely word-final -h, vowels, and nasals caused initial mutations if possible, possibly by resegmentation onto the following word. Any remaining final-syllable short vowels, -h, and nasals after this stage are deleted, while remaining final long vowels (which were subsequently shortened in Old Irish) remained. It is also apparent in Ogham inscriptions that final-syllable Proto-Celtic *o had become *a by Primitive Irish before its loss.
In the following table, the cover symbol C refers to any consonant.
After the general final-syllable deletion processes, newly word-final consonant clusters ending in sonorant consonants like liquids and nasals in early Irish that were not simplified with compensatory lengthening gained a schwa between the sonorant and the rest of the cluster. The schwa was often rendered with rounded vowel letters like o or u in early texts if next to a labial consonant. For instance:
Voiceless obstruents, including voiceless stops and voiceless fricatives, were often voiced word-initially and word-finally in unstressed syllables. Each type of voiceless obstruent however had different triggers for them being voiced. These voicings occurred around AD 700. These voicings are collectively labelled McCone's law by David Stifter after their main formulator Kim McCone.
Dental obstruents were voiced in word-initial and word-final unstressed syllables, in addition to between two unstressed syllables. This wave of voicing is also believed to underlie the voicing of t- to d- in proclitics.
Happening along with the voicing of dental obstruents was the voicing of f to , spelled b. The voicing of f has been believed to occur in near-identical environments to the voicing of dentals. Schrijver and McCone think the voicing of f could also happen word-finally in stressed syllables as well, but Stifter is not confident in the evidence.
Palatalised voiceless velar fricatives became their voiced counterparts word-finally and between unstressed vowels.
This voicing of palatalised velar fricatives created paradigmatic alternations in noun declension where final unpalatalised voiceless velar fricatives alternated with palatalised voiced velar fricatives. Occasionally, nouns originally ending in non-palatal in their paradigms had those unpalatalised voiced velar fricatives analogically devoiced to , for instance in < < "house".
Intervocalic single Proto-Celtic *-s- was lenited to -h- and then lost in the following manners:
Vowels surrounding a former intervocalic -s-, a glide *w or *y, or both underwent special changes by Old Irish.
In unstressed syllables, such vowels generally fused into /e/.
Proclitics that precede a stressed syllable undergo special sound changes during the Old Irish period.
Initial s was deleted in proclitics.
Initial t in pretonic position was voiced to d-.
Long vowels merged with their corresponding short vowels in proclitics.
This was followed by o merging with u, with the resulting vowel spelled with both u and o in Old Irish.
At the same time, e became a in proclitics, except for e before *nt which instead merged with i with the spelling vacillating between e and i.
Palatalisation was generally lost in proclitics.
The following are some examples of changes between Primitive Irish and Old Irish.
These various changes, especially syncope, produced quite complex allomorphy, because the addition of prefixes or various pre-verbal particles (proclitics) in Proto-Celtic changed the syllable containing the stress: According to the Celtic variant of Wackernagel's law, the stress fell on the second syllable of the verbal complex, including any prefixes and clitics. By the Old Irish period, most of this allomorphy still remained, although it was rapidly eliminated beginning in the Middle Irish period.
Among the most striking changes are in prefixed verbs with or without pre-verbal particles. With a single prefix and without a proclitic, stress falls on the verbal root, which assumes the deuterotonic ("second-stressed") form. With a prefix and also with a proclitic, stress falls on the prefix, and the verb assumes the prototonic ("first-stressed") form. Rather extreme allomorphic differences can result:
The following table shows how these forms might have been derived:
The most extreme allomorphy of all came from the third person singular of the -subjunctive because an athematic person marker was used, added directly onto the verbal stem (formed by adding directly onto the root). That led to a complex word-final cluster, which was deleted entirely. In the prototonic form (after two proclitics), the root was unstressed and thus the root vowel was also deleted, leaving only the first consonant: