In linguistics, lenition is a sound change that alters consonants, making them more sonorous. The word lenition itself means "softening" or "weakening" (from Latin 'weak'). Lenition can happen both synchronically (within a language at a particular point in time) and diachronically (as a language changes over time). Lenition can involve such changes as voicing a voiceless consonant, causing a consonant to relax occlusion, to lose its place of articulation (a phenomenon called debuccalization, which turns a consonant into a glottal consonant like or ), or even causing a consonant to disappear entirely.
An example of synchronic lenition is found in most varieties of American English, in the form of flapping: the of a word like wait is pronounced as the more sonorous in the related form waiting . Some varieties of Spanish show debuccalization of to at the end of a syllable, so that a word like "we are" is pronounced . An example of diachronic lenition can be found in the Romance languages, where the of Latin ("father", accusative) has become in Italian and Spanish (the latter weakened synchronically → ), while in Catalan , French and Portuguese historical has disappeared completely.
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 "cat" begins with the sound , but after the definite article , the changes to : "the cat" in Welsh is . This was historically due to intervocalic lenition, but in the plural, lenition does not happen, so "the cats" is , not *. The change of to in is thus caused by the syntax of the phrase, not by the modern phonological position of the consonant .
The opposite of lenition, fortition, a sound change that makes a consonant "stronger", is less common, but Breton and Cornish have "hard mutation" forms which represent fortition.
Types
Lenition involves changes in manner of articulation, sometimes accompanied by small changes in place of articulation. There are two main lenition pathways: opening and sonorization. In both cases, a stronger sound becomes a weaker one. Lenition 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.
In examples below, a greater-than sign indicates that one sound changes to another. The notation > means that changes to .
The sound change of palatalization sometimes involves lenition.
Lenition includes the loss of a feature, such as deglottalization, in which glottalization or ejective articulation is lost: or > .
The tables below show common sound changes involved in lenition. In some cases, lenition may skip one of the sound changes. The change voiceless stop > fricative is more common than the series of changes voiceless stop > affricate > fricative.
Opening
In the opening type of lenition, the articulation becomes more open with each step. Opening lenition involves several sound changes: shortening of double consonants, affrication of stops, spirantization or assibilation of stops or affricates, debuccalization, and finally elision. or > (shortening) > (affrication, for example to ) or > (spirantization, example in Gilbertese language) > ; > (debuccalization, example in English or Spanish) , , , , > ∅ (elision)
Sonorization
The sonorization type involves voicing. Sonorizing lenition involves several sound changes: voicing, approximation, and vocalization. > (voicing, example in Korean) > (approximation, example in Spanish) > (vocalization)
Sonorizing 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.
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 → → and → → . 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 → or → .