In linguistics, lenition is a kind of consonant mutation that appears in many languages. Along with assimilation, it is one of the primary sources of historical change of languages.
Lenition means "softening" or "weakening" (from Latin lenis = weak), and it refers to the change of a consonant considered "stronger" into one considered "weaker" (or fortis → lenis). Common examples include voicing or sonorization, as in → ; affrication or spirantization (turning into an affricate or a fricative), as in → → ; debuccalization (loss of place), as in → ; degemination, as in → ; deglottalization, such as → , 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.

Sound changes associated with lenition

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

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

Lenition can be seen in Canadian and American English, where and soften to a tap after a stressed vowel. For example, both write and ride plus the suffix -er are pronounced (though in many dialects the i vowel differs), 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 [ˈt͡ʃeː.na] 'dinner' but post-vocalic la cena [laˈʃeː.na] 'the dinner'; the name Luciano, although structurally /luˈt͡ʃaː.no/, is normally pronounced [luˈʃaː.no].

These pathways may become mixed. For example, may spirantize to , then sonorize to . However, whereas sounds change easily in these directions, change in the opposite direction (fortition) generally requires a specific triggering environment.

Diachronic lenition

Diachronic lenition is found, for example, in the change from Latin into Spanish, in which the intervocalic voiceless stops first changed into their voiced counterparts , and later into the approximants : vita → vida, caput → cabo, caecus → ciego.

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 /tʰuaθ/ and ultimately complete deletion 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. 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 > /kopa/ 'cup' (compare geminate-preserving Italian /kɔppa/) is often viewed as a type of lenition.

Synchronic lenition

Allophonic lenition (sandhi)

Like several 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.

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 [kaːsa] casa 'house' in a post-pause realization, [iŋkaːsa] in casa 'in (the) house' post-consonant, but [lahaːsa] la casa 'the house' intervocalically. Word-internally, the normal realization is also [h]: /buko/ buco 'hole' → [buːho].

Grammatical lenition

In the Celtic languages, the phenomenon of intervocalic lenition extended across word boundaries, as it does today in much of Italy and in Corsica. 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 ('the man') and lenition in a’ bhean ('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:

Synchronic lenition in Scottish Gaelic affects almost all consonants (except which has lost its lenited counterpart).Oftedal, M. (1956) The Gaelic of Leurbost Norsk Tidskrift for Sporgvidenskap, Oslo Changes such as to involve the loss of secondary articulation; in addition, → involves the reduction of a trill to a tap. The spirantization of Gaelic nasal to 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):

Orthography

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, 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 [t̪ʰɤj] "house" → an taigh [ən̪ˠˈd̪ʰɤj] "the house".

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- "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 , though these have been lost in favour of similar-sounding phonemes. In Pohjanmaa Finnish, was changed into , thus the dialect has a synchronic lenition of an alveolar stop into an alveolar trill . Furthermore, the same phoneme undergoes assibilation → before the vowel , 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

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 > gennaio, with ) and synchronically (e.g. "house, home" → but "at home" → ). Catalan is among numerous Romance languages with diachronic word-final fortition (frigidu > > "cold"). Word-medially, is subject to fortition in numerous Romance languages, ranging from in many speech types on Italian soil to in some varieties of Spanish.

See also

• Apophony

• Chain shift

• Consonant mutation

• Grimm's Law

• Historical linguistics

• Intervocalic alveolar flapping

• Germanic spirant law