|Sound change and alternation|
In linguistics, lenition is a kind of sound change that alters consonants, making them more sonorous. The word lenition itself means "softening" or "weakening" (from Latin lenis = weak). Lenition can happen both synchronically (i.e., within a language at a particular point in time) and diachronically (i.e. as a language changes over time). Lenition can involve such changes as making a consonant more sonorous (vowel-like), causing a consonant to lose its place of articulation (a phenomenon called debuccalization, which turns a consonant into a glottal consonant like [h] or [ʔ]), or even causing a consonant to disappear entirely.
An example of synchronic lenition in English is found in flapping in some dialects: the /t/ of a word like wait [weɪt] becomes the more sonorous [ɾ] in the related form waiting [ˈweɪɾɪŋ]. Some dialects of Spanish show debuccalization of /s/ to [h] at the end of a syllable, so that a word like estamos "we are" is pronounced [ehˈtamoh]. An example of diachronic lenition can be found in the Romance languages, where the /t/ of Latin patrem ("father", accusative) becomes [d] in Italian padre and [ð̞] in Spanish padre, while in French père and Portuguese pai it has disappeared completely. Along with assimilation, lenition is one of the primary sources of phonological change of languages.
In some languages, lenition has been grammaticalized into a consonant mutation, which means it is no longer triggered by its phonological environment but is now governed by its syntactic or morphological environment. For example, in Welsh, the word cath "cat" begins with the sound /k/, but after the definite article y, the /k/ changes to [ɡ]: "the cat" in Welsh is y gath. This was historically due to intervocalic lenition, but in the plural, lenition does not happen, so "the cats" is y cathod, not *y gathod. The change of /k/ to [ɡ] in y gath is thus caused by the syntax of the phrase, not by the phonological position of the consonant /k/.
The opposite of lenition is fortition, a sound change making a consonant "stronger".
Common characteristics 
Common examples include voicing or sonorization, as in [f] → [v]; affrication or spirantization (turning into an affricate or a fricative), as in [t] → [ts] → [s]; debuccalization (loss of place), as in [s] → [h]; degemination, as in [kː] → [k]; deglottalization, such as [kʼ] → [k], etc. These may occur one after the other in the history of a language. Eventually, consonants may be lost completely, which is the ultimate lenition. Lenition, then, can be seen as a movement on the sonority hierarchy from less sonorous to more sonorous, or on a strength hierarchy from stronger to weaker.
Lenition occurs especially often intervocalically (between vowels). In this position, lenition can be seen as a type of assimilation of the consonant to the surrounding vowels, in which features of the consonant that are not present in the surrounding vowels (e.g. obstruction, voicelessness) are gradually eliminated.
The opposite of lenition is called fortition, which is a less common sound change.
Sound changes associated with lenition 
Two common lenition pathways are the "opening" type, where the articulation becomes more open with each step,
|geminated stop||→||stop||→||affricate||→||fricative||→||placeless approximant||→||no sound|
|[pp] or [ppʰ]||→||[p] or [pʰ]||→||[pɸ]||→||[ɸ]||→||[h]||→||(zero)|
|[tt] or [ttʰ]||→||[t] or [tʰ]||→||[tθ]||→||[θ]||→|
|[kk] or [kkʰ]||→||[k] or [kʰ]||→||[kx]||→||[x]||→|
and the "sonorization" type, which involves voicing as well,
(fricative, tap, etc.)
Note: Some of the sounds generated by lenition are often subsequently "normalized" into related but cross-linguistically more common sounds. An example would be the changes [b] → [β] → [v] and [d] → [ð] → [z]. Such normalizations correspond to diagonal movements down and to the right in the above table. In other cases sounds are lenited and normalized at the same time; examples would be direct changes [b] → [v] or [d] → [z].
In some cases, a lenition change may "skip" one of the columns in the above tables. This is particularly common in the case of the direct change voiceless stop → fricative, which is more common than a series of changes voiceless stop → affricate → fricative.
The above pathways may also become mixed. For example, [kʰ] may spirantize to [x], then sonorize to [ɣ].
Lenition can be seen in Canadian and American English, where [t] and [d] soften to a tap [ɾ] after a stressed vowel. For example, both rate and raid plus the suffix -er are pronounced [ˈɹeɪ̯ɾɚ], whereas in most British English dialects there is no such lenition. (See Intervocalic alveolar flapping.) The Italian of Central Italy has a number of lenitions, the most widespread of which is the deaffrication of /t͡ʃ/ to [ʃ] between vowels: post-pausal cena [ˈt͡ʃeːna] 'dinner' but post-vocalic la cena [laˈʃeːna] 'the dinner'; the name Luciano, although structurally /luˈt͡ʃaːno/, is normally pronounced [luˈʃaːno].
Diachronic lenition 
Diachronic lenition is found, for example, in the change from Latin into Spanish, in which the intervocalic voiceless stops [p t k] first changed into their voiced counterparts [b d ɡ], and later into the approximants or fricatives [β̞ ð̞ ɣ̞]: vita → vida, lupa → loba, caeca → ciega.
A similar development occurred in the Celtic languages, where non-geminate intervocalic consonants were converted into their corresponding weaker counterparts through lenition (usually stops into fricatives but also laterals and trills into weaker laterals and taps), and voiceless stops became voiced. For example, Indo-European intervocalic -t- in *teu̯teh₂ "people" resulted in Proto-Celtic *tou̯tā, Primitive Irish *tōθā, Old Irish túath /tuaθ/ and ultimately complete deletion in modern Scots Gaelic tuath /t̪ʰuə/.
An example of historical lenition in the Germanic languages is evidenced by English-Latin cognates such as pater, tenuis vs. father, thin. The Latin words preserved the original stops, which became fricatives in old Germanic by Grimm's law. Although actually a much more profound change encompassing syllable restructuring, simplification of geminate consonants as in the passage from Latin to Spanish such as CUPPA > /ˈkopa/ 'cup' (compare geminate-preserving Italian /ˈkɔppa/) is often viewed as a type of lenition.
Synchronic lenition 
Allophonic lenition (sandhi) 
Like other Western Romance languages, many varieties of Sardinian offer an example of sandhi where the rule of intervocalic lenition extends across word boundaries. Since it is a fully active synchronic rule, lenition is not normally indicated in the normal orthography.
|/b/||→ [β]: baca [ˈbaka] "cow" → sa baca [sa ˈβaka] "the cow"|
|/d/||→ [ð]: domu [ˈdɔmu] "house" → sa domu [sa ˈðɔmu] "the house"|
|/ɡ/||→ [ɣ]: gupu [ˈɡupu] "ladle" → su gupu [su ˈɣupu] "the ladle"|
A series of synchronic lenitions involving opening, or loss of occlusion, rather than voicing is found for post-vocalic /p t k/ in much of Tuscany, in Central Italy. Stereotypical Florentine, for example, has the /k/ of /kasa/ as [ˈkaːsa] casa 'house' in a post-pause realization, [iŋˈkaːsa] in casa 'in (the) house' post-consonant, but [laˈhaːsa] la casa 'the house' intervocalically. Word-internally, the normal realization is also [h]: /ˈbuko/ buco 'hole' → [ˈbuːho].
Grammatical lenition 
In the Celtic languages, the phenomenon of intervocalic lenition historically extended across word boundaries. This explains the rise of grammaticalised initial consonant mutations in modern Celtic languages through the loss of endings. A Scottish Gaelic example would be the lack of lenition in am fear /əm fɛr/ ('the man') and lenition in a’ bhean /ə vɛn/ ('the woman'). The following examples show the development of a phrase consisting of a definite article plus a masculine noun (taking the ending -os) compared with a feminine noun taking the ending -a. The historic development of lenition in these two cases can be reconstructed as follows:
- Proto-Celtic *(s)indos wiros IPA: [wiɾos] → Old Irish ind fer [feɾ] → Middle Irish in fer [feɾ] → Classical Gaelic an fear [feɾ] → Modern Gaelic am fear [fɛɾ]
- Proto-Celtic *(s)indā benā IPA: [venaː] → Old Irish ind ben [ven] → Middle Irish in ben [ven] → Classical Gaelic an bhean [ven] → Modern Gaelic a' bhean [vɛn]
Synchronic lenition in Scottish Gaelic affects almost all consonants (except /l̪ˠ/ which has lost its lenited counterpart). Changes such as /n̪ˠ/ to /n/ involve the loss of secondary articulation; in addition, /rˠ/ → /ɾ/ involves the reduction of a trill to a tap. The spirantization of Gaelic nasal /m/ to /v/ is unusual among forms of lenition, but is triggered by the same environment as more prototypical lenition. (It may also leave a residue of nasalization in adjacent vowels. The orthography shows this by inserting an h (except after l n r):
|/p/||→ /v/||bog /pok/ "soft" → glé bhog /kleː vok/ "very soft"|
|/pj/||→ /vj/ (before a back vowel)||beò /pjɔː/ 'alive' → glé bheò /kleː vjɔː/ 'very alive'|
|/kʰ/||→ /x/||cas /kʰas̪/ "steep" → glé chas /kleː xas̪/ "very steep"|
|/kʰʲ/||→ /ç/||ciùin /kʰʲuːɲ/ "quiet" → glé chiùin /kleː çuːɲ/ "very quiet"|
|/t̪/||→ /ɣ/||dubh /t̪uh/ "black" → glé dhubh /kleː ɣuh/ "very black"|
|/tʲ/||→ /ʝ/||deiseil /tʲeʃal/ "ready" → glé dheiseil /kleː ʝeʃal/ "very ready"|
|/k/||→ /ɣ/||garbh /kaɾav/ "rough" → glé gharbh /kleː ɣaɾav/ "very rough"|
|/kʲ/||→ /ʝ/||geur /kʲiaɾ/ "sharp" → glé gheur /kleː ʝiaɾ/ "very sharp"|
|/m/||→ /v/||maol /mɯːl̪ˠ/ "bald" → glé mhaol /kleː vɯːl̪ˠ/ "very bald"|
|/mj/||→ /vj/ (before a back vowel)||meallta /mjaul̪ˠt̪ə/ "deceitful" → glé mheallta /kleː vjaul̪ˠt̪ə/ "very deceitful"|
|/pʰ/||→ /f/||pongail /pʰɔŋɡal/ "exact" → glé phongail /kleː fɔŋɡal/ "very exact"|
|/pʰj/||→ /fj/ (before a back vowel)||peallagach /pʰjal̪ˠakəx/ "shaggy" → glé pheallagach /kleː fjal̪ˠakəx/ "very shaggy"|
|Loss of secondary articulation|
|/n̪ˠ/||→ /n/||nàdarra /n̪ˠaːt̪ərˠə/ "natural" → glé nàdarra /kleː naːt̪ərˠə/ "very natural"|
|/rˠ/||→ /ɾ/||rag /rˠak/ "stiff" → glé rag /kleː ɾak/ "very stiff"|
|/s̪/||→ /h/||sona /s̪ɔnə/ "happy" → glé shona /kleː hɔnə/ "very happy"|
|/ʃ/||→ /h/||seasmhach /ʃes̪vəx/ "constant" → glé sheasmhach /kleː hes̪vəx/ "very constant"|
|/ʃ/||→ /hj/ (before a back vowel)||seòlta /ʃɔːl̪ˠt̪ə/ "sly" → glé sheòlta /kleː hjɔːl̪ˠt̪ə/ "very sly"|
|/t̪ʰ/||→ /h/||tana /t̪ʰanə/ "thin" → glé thana /kleː hanə/ "very thin"|
|/tʰʲ/||→ /h/||tinn /tʲiːɲ/ "ill" → glé thinn /kleː hiːɲ/ "very ill"|
|/tʰʲ/||→ /hj/ (before a back vowel)||teann /tʰʲaun̪ˠ/ "tight" → glé theann /kleː hjaun̪ˠ/ "very tight"|
|/f/||→ Ø||fann /faun̪ˠ/ "faint" → glé fhann /kleː aun̪ˠ/ "very faint"|
|/fj/||→ /j/ (before a back vowel)||feòrachail /fjɔːɾəxal/ "inquisitive" → glé fheòrachail /kleː jɔːɾəxal/ "very inquisitive"|
|Reduction of place markedness|
|In the modern Goidelic languages, grammatical lenition also triggers the reduction of markedness in the place of articulation of coronal sonorants (l, r, and n sounds). In Scottish Gaelic, /n/ and /l/ are the weak counterparts of palatal /ɲ/ and /ʎ/.|
|/ɲ/||→ /n/||neulach /ɲial̪ˠəx/ "cloudy" → glé neulach /kleː nial̪ˠəx/ "very cloudy"|
|/ʎ/||→ /l/||leisg /ʎeʃkʲ/ "lazy" → glé leisg /kleː leʃkʲ/ "very lazy"|
Blocked lenition 
Some languages which have lenition also have complex rules affecting instances of where lenition might be expected but does not occur. Such instances often involve homorganic consonants. In Scottish Gaelic for example there are 3 homorganic groups:
- d n t l s (usually called the dental group in spite of the non-dental nature of the palatals)
- c g (usually called the velar group)
- b f m p (usually called the labial group)
In a position where lenition is expected due to the grammatical environment, lenition tends to be blocked if there are two adjacent homorganic consonants across the word boundary. For example:
- aon 'one' (which causes lenition) → aon chas 'one leg' vs aon taigh 'one house' (not aon *thaigh)
- air an 'on the' (which causes lenition) → air a' chas mhòr 'on the big leg' vs air an taigh donn 'on the brown house' (not air an *thaigh *dhonn)
In modern Scottish Gaelic this rule is only productive in the case of dentals but not the other two groups for the vast majority of speakers. It also does not affect all environments any more, for example while aon still invokes the rules of blocked lenition, a noun followed by an adjective generally no longer does so. Hence:
- ad 'hat' (a feminine noun causing lenition) → ad dhonn 'a brown hat' (although some highly conservative speakers retain ad donn)
- caileag 'girl' (a feminine noun causing lenition) → caileag ghlic 'a smart girl' (not caileag *glic)
The is a significant number of frozen forms involving the other two groups (labials and velars) and environments, especially in surnames and place names:
- MacGumaraid 'Montgomery' (mac + Gumaraid) vs MacDhòmhnaill 'MacDonald (mac + Dòmhnall)
- Caimbeul 'Campbell' (cam 'crooked' + beul 'mouth') vs Camshron 'Cameron' (cam + sròn 'nose')
- sgian-dubh 'Sgian-dubh' (sgian 'knife' + dubh '1 black 2 hidden'; sgian as a feminine noun today would normally cause lenition on a following adjective) vs sgian dhubh 'a black knife' (i.e. a common knife which just happens to be black)
Though rare, in some instances the rules of blocked lenition can be invoked by lost historical consonants, for example in the case of the past-tense copula bu which in Common Celtic had a final -t. In terms of blocked lenition it continues to behave as a dental-final particle invoking blocked lenition rules:
- bu dona am biadh 'bad was the food' vs bu mhòr am beud 'great was the pity
Blocked lenition phenomena are also known to occur in Irish and Spanish (orthographic b d g retained as /b/, /d/, /ɡ/ following nasals rather than their normal lenited forms [β, ð, ɣ]).
In the modern Celtic languages, lenition of the "fricating" type is usually denoted by adding an h to the lenited letter. In Welsh, for example, c, p and t change into ch, ph, th as a result of the so-called "aspirate mutation" (carreg, "stone" → ei charreg "her stone"). An exception is Manx orthography, which tends to be more phonetic, although in some cases etymological principles are applied. In the Gaelic script, fricating lenition (called simply lenition in Irish grammar contexts) is indicated by a dot above the affected consonant, while in the Roman script, the convention is to suffix the letter h to the consonant, to signify that it is lenited. Thus, a ṁáṫair is equivalent to a mháthair. In Middle Irish manuscripts, lenition of s and f was indicated by the dot above, while lenition of p, t, and c was indicated by the postposed h; lenition of other letters was not indicated consistently in the orthography.
Voicing lenition is represented by a simple letter switch in the Brythonic languages, for instance carreg, "stone" → y garreg, "the stone" in Welsh. In Irish orthography, it is shown by writing the "weak" consonant alongside the (silent) "strong" one: peann, "pen" → ár bpeann "our pen", ceann, "head" → ár gceann "our head" (sonorization is traditionally called "eclipsis" in Irish grammar). Although it also occurs in most Scottish Gaelic dialects, it is not written as it is synchronic (i.e. the result of certain types of preceding nasal, rather than the diachronic Irish type sonorization (i.e. following historic nasals); for example taigh [t̪ˠʰɤj] "house" → an taigh [ən̪ˠˈd̪ˠʰɤj] "the house".
Consonant gradation 
An example with geminate consonants comes from Finnish, where geminates become simple consonants while retaining voicing or voicelessness (e.g. katto → katon, dubbaan → dubata). It is also possible for entire consonant clusters to undergo lenition, as in Votic, where voiceless clusters become voiced, e.g. itke- "to cry" → idgön.
If a language has no obstruents other than voiceless stops, other sounds are encountered, as in Finnish, where the lenited grade is represented by chronemes, approximants, taps or even trills. For example, Finnish used to have a complete set of spirantization reflexes for /p t k/, though these have been lost in favour of similar-sounding phonemes. In Pohjanmaa Finnish, /ð/ was changed into /r/, thus the dialect has a synchronic lenition of an alveolar stop into an alveolar trill /t/ → /r/. Furthermore, the same phoneme /t/ undergoes assibilation /t/ → /s/ before the vowel /i/, e.g. root vete- "water" → vesi and vere-. Here, vete- is the stem, vesi is its nominative, and vere- is the same stem under consonant gradation.
Fortition is a consonant mutation in which a sound is changed from one considered "weak" to one considered "strong" – the opposite of lenition. Although less frequent than lenition in the languages of the world, word-initial and word-final fortition is not uncommon. Italian, for example, presents numerous regular examples of word-initial fortition both historically (Lat. Januarius with initial /j/ > gennaio, with [dʒ]) and synchronically (e.g. /ˈkasa/ "house, home" → [ˈkaːsa] but /a ˈkasa/ "at home" → [aˈkːaːsa]). Catalan is among numerous Romance languages with diachronic word-final devoicing (frigidus > */ˈfɾɛd/ > [ˈfɾɛt]. Fortition also occur in Catalan for /b d ɡ/ in consonant clusters with a lateral consonant (Lat. populus > poble [ˈpɔbːɫə] or [ˈpɔpːɫə]. Word-medially, /lː/ is subject to fortition in numerous Romance languages, ranging from [dː] in many speech types on Italian soil to [dʒ] in some varieties of Spanish.
See also 
- Rendaku (a similar phenomenon in the Japanese language)
- Chain shift
- Consonant mutation
- Grimm's Law
- Historical linguistics
- Germanic spirant law
- Stifter, D. Sengoídelc Syracuse University: 2006 ISBN 0-8156-3072-7
- Mensching, G. (1992) Einführung in die Sardische Sprache Romanistischer Verlag, Bonn
- Oftedal, M. (1956) The Gaelic of Leurbost Norsk Tidskrift for Sporgvidenskap, Oslo
- Ternes, E. (1989) The Phonemic Analysis of Scottish Gaelic Helmut Buske Verkag, Hamburg
- Bauer, Michael Blas na Gàidhlig - The Practical Guide to Gaelic Pronunciation (2011) Akerbeltz ISBN 978-1-907165-00-9
- Ó Maolalaigh, R. Scottish Gaelic in Three Months (1996) Hugo's Language Books ISBN 0-85285-234-7
General references 
- Crowley, Terry. (1997) An Introduction to Historical Linguistics. 3rd edition. Oxford University Press.
- Magne Oftedal Lenition in Celtic and in Insular Spanish Universitetsforlaget AS 1985. ISBN 82-00-07282-7