Lenition is a kind of consonant mutation that appears in many languages. Along with assimilation, it is one of the primary sources of the historical change of languages.

Lenition means 'softening' or 'weakening' (from Latin lenis, the root of 'lenient'), and it refers to the change of a consonant considered 'strong' into one considered 'weak' (fortis → lenis). Common examples include voicing or sonorization, as in [f] → [v]; affrication or spirantization (turning into an affricate or a fricative), as in [t] → [ts] or [s]; debuccalization (loss of place), as in [s] → [h]; degemination, as in [k:] → [k]; deglottalization, such as [k’] → [k], etc. Ultimately, consonants may be lost completely. Lenition, then, can be seen as a movement on the sonority scale from less sonorous to more sonorous.

Common types of lenition

Two common lenition pathways are the "opening" type, where the articulation becomes more open with each step,

stop	→	affrication	→	spirantization	→	debuccalization	→	elision
[p] or [pʰ]	→	[pf] or [pɸ]	→	[f] or [ɸ]	→	[h]	→	(zero)
[t] or [tʰ]	→	[ts] or [tθ]	→	[s] or [θ]	→	[h]	→	(zero)
[k] or [kʰ]	→	[kx]	→	[x]	→	[h]	→	(zero)

and the "sonorization" type, which involves voicing as well as opening,

stop	→	sonorization	→	spirantization	→	approximation	→	elision
[p]	→	[b]	→	[v] or [β]	→	[ʋ] or [β̞]	→	(zero)
[t]	→	[d]	→	[ğ] or [z]	→	[ğ̞] or [ɹ]	→	(zero)
[k]	→	[g]	→	[ɣ]	→	[ɰ]	→	(zero)

These pathways may become mixed. For example, [kʰ] may spirantize to [x], then sororize to [ɣ]. However, whereas sounds change easily in these directions, change in the opposite direction generally requires a specific triggering environment.

Some examples

Diachronic lenition is found, for example, in the change from Latin into Spanish, where voiceless stops [p t k] changed into their voiced counterparts [β̞ ğ̞ ɰ]: vita → vida, caput → cabo, caecus → ciego. A similar development occurred in the Celtic languages where non-geminate intervocalic voiced consonants were converted into fricatives through lenition, and voiceless stops became voiced (in Welsh, Cornish and Breton). 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.

Sardinian offers a nice example of synchronic lenition where the rule of intervocalic lenition is so strong it even extends across word boundaries. Since it is a fully active synchronic rule, lenition is not normally indicated in the normal orthography.

/b/	→ [β] bacca [bakka] 'cow' → sa bacca [sa βakka] 'the cow'
/d/	→ [ğ] domu [dɔmu] 'house' → sa domu [sa ğɔmu] 'the house'
/g/	→ [ɣ] guppu [guppu] 'ladle' → sa guppu [sa ɣuppu] 'the ladle'

In the Celtic languages

In Celtic, the phenomenon of intervocalic lenition extended across word boundaries. This explains the rise of grammaticalised initial consonant mutation 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:

Old Celtic *(s)indos wiros → OIr. ind fer → in fer → an fear → am fear

Old Celtic *(s)inda bena → OIr. ind ḃen → in ḃen → an bhean → a' bhean

Lenition in Scots Gaelic affects almost all consonants (except /ɫ̪/ which has lost its lenited counterpart). The normal orthography shows this by inserting an h (except with l n r):

/b̊/	→ /v/	bog /b̊og̊/ → glé bhog /g̊leː vog̊/
/b̊j/	→ /vj/ (preceding a back vowel)	beò /b̊jɔː/ 'alive' → glé bheò /g̊leː vjɔː/ 'very alive'
/k/	→ /x/	cas /kas̪/ 'steep' → glé chas /g̊leː xas̪/ 'very steep'
/kʲ/	→ /ç/	ciùin /kʲuːɲ/ 'quiet' → glé chiùin /g̊leː çuːɲ/ 'very quiet'
/d̪̊/	→ /ɣ/	dubh /d̪̊uh/ 'black' → glé dhubh /g̊leː ɣuh/ 'very steep'
/d̥ʲ/	→ /ʝ/	deiseil /d̥ʲeʃal/ 'ready' → glé dheiseil /g̊leː ʝeʃal/ 'very ready'
/f/	→ Ø	fann /faun̴̪/ 'faint' → glé fhann /g̊leː aun̴̪/ 'very faint'
/fj/	→ /j/ (preceding a back vowel)	feòrachail /fjɔːɾəxal/ 'inquisitive' → glé fheòrachail /g̊leː jɔːɾəxal/ 'very inquisitve'
/g̊/	→ /ɣ/	garbh /g̊aɾav/ 'rough' → glé gharbh /g̊leː ɣaɾav/ 'very rough'
/g̊ʲ/	→ /ʝ/	geur /g̊ʲiaɾ/ 'sharp' → glé gheur /g̊leː ʝiaɾ/ 'very sharp'
/ʎ/	→ /l/	leisg /ʎeʃg̊ʲ/ 'lazy' → glé leisg /g̊leː leʃg̥ʲ/ 'very lazy'
/m/	→ /v/	maol /mɯːɫ̪/ 'bald' → glé mhaol /g̊leː vɯːɫ̪/ 'very bald'
/mj/	→ /vj/ (preceding a back vowel)	meallta /mʲauɫ̪d̪̊ə/ 'deceitful' → glé mheallta /g̊leː vjauɫ̪d̪̊ə/ 'very deceitful'
/n̴̪/	→ /n/	nàdarra /n̴̪aːd̪̊ər̴ə/ 'natural' → glé nàdarra /g̊leː naːd̪̊ər̴ə/ 'very natural'
/ɲ/	→ /n/	neulach /ɲiaɫ̪əx/ 'cloudy' → glé neulach /g̊leː niaɫ̪əx/ 'very cloudy'
/p/	→ /f/	pongail /pɔŋgal/ 'exact' → glé phongail /g̊leː fɔŋgal/ 'very exact'
/pj/	→ /fj/ (preceding a back vowel)	peallagach /pjaɫ̪ag̊əx/ 'shaggy' → glé pheallagach /g̊leː fjaɫ̪ag̊əx/ 'very shaggy'
/r̴/	→ /ɾ/	rag /r̴ag̊/ 'stiff' → glé rag /g̊leː ɾag̊/ 'very steep'
/s̪/	→ /h/	sona /s̪ɔnə/ 'happy' → glé shona /g̊leː hɔnə/ 'very happy'
/ʃ/	→ /h/ (/hj/ preceding a back vowel)	seasmhach /ʃes̪vəx/ 'constant' → glé sheasmhac /g̊leː hes̪vəx/ 'very constant'
	seòlta /ʃɔːɫ̪d̪̊ə/ 'sly' → glé sheòlta /g̊leː hjɔːɫ̪d̪̊ə/ 'very sly'
/t̪/	→ /h/	tana /t̪anə/ 'thin' → glé thana /g̊leː hanə/ 'very thin'
/tʲ/	→ /h/ (/hj/ preceding a back vowel)	tinn /tʲiːɲ/ 'ill' → glé thinn /g̊leː hiːɲ/ 'very ill'
	teann /tʲaun̴̪/ 'tight' → glé theann /g̊leː hjaun̴̪/ 'very tight'

Orthography

In the modern Celtic languages of the British Isles, lenition of the 'opening' 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'). In late Gaelic calligraphy and in traditional Irish typography, opening lenition (simply called 'lenition' in Irish grammar) was indicated by a dot above the affected consonant. However, since few typesetters had the requisite slug, their convention has been to suffix the letter h to the consonant, to signify that it is lenited. For example, a mháthair (as above) is a Latin alphabet rendering of a ṁáṫair.

Sonorization-type 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' → bpeann, ceann 'head' → gceann (sonorization is traditionally called 'eclipsis' in Irish grammar).

For more details, see Welsh morphology and Irish initial mutations.

Consonant gradation

Main article: Consonant gradation

The phenomenon of consonant gradation in Samic and Baltic-Finnic languages is also a form of lenition.

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- → idgön.

If a language has nothing but voiceless stops, other sounds are encountered, as in Finnish, where fricatives are 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, /ğ/ 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 te → si, e.g. root vete- → vesi and vere-. Here, vete- is the stem, vesi is its nominative, and vere- is the same stem under consonant gradation.

Fortition

Main article: Fortition

A consonant mutation in which a sound is changed from one considered 'weak' to one considered 'strong', the opposite of lenition, is called fortition. Fortition is a much rarer sound change than lenition, and is not found in many languages.

See also

• Apophony
• Consonant mutation
• Grimm's Law
• Historical linguistics
• Intervocalic alveolar flapping
• Spirantization