Lenition

Lenition is a type of sound change in which a consonant becomes "weaker," a process also described as softening or weakening. The word itself comes from the Latin *lēnis*, meaning 'weak'. This change can happen in two ways: synchronically, meaning within a language at a single point in time, or diachronically, as a language evolves over time.

The weakening can take several forms. A voiceless consonant may become voiced, its occlusion may relax, it might lose its place of articulation entirely (a process called debuccalization, which turns a consonant into a glottal sound like [h] or [ʔ]), or the consonant may even disappear completely.

A common synchronic example is tapping in most varieties of American English. The /t/ in *wait* [weɪt] becomes the more sonorous [ɾ] in the related word *waiting* [ˈweɪɾɪŋ]. In some Spanish dialects, debuccalization of /s/ to [h] occurs at the end of a syllable, so *estamos* ("we are") is pronounced [ehˈtamoh]. A diachronic example comes from the Romance languages. The /t/ in the Latin word *patrem* ("father", accusative) became /d/ in Italian (an irregular change) and Spanish *padre* (where the /d/ weakens synchronically to [ð̞]), while in Catalan *pare*, French *père*, and Portuguese *pai*, the historical /t/ has vanished entirely.

In some languages, lenition has been grammaticalized into a consonant mutation. This means it is no longer triggered by the phonological environment but instead by syntactic or morphological rules. For instance, in Welsh, the word *cath* ("cat") begins with /k/, but after the definite article *y*, the /k/ changes to [ɡ], giving *y gath* ("the cat"). This was historically due to intervocalic lenition, but in the plural, lenition does not occur, so "the cats" is *y cathod*, not *y gathod*. The change of /k/ to [ɡ] in *y gath* is therefore caused by syntax, not by the modern phonological position of the consonant.

The opposite of lenition is fortition, a sound change that makes a consonant "stronger." Fortition is less common, though Breton and Cornish have "hard mutation" forms that represent it.

**Types**

Lenition involves changes in manner of articulation, sometimes with small changes in place of articulation. There are two main pathways: opening and sonorization. In both, 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. The sound change of palatalization sometimes involves lenition. Lenition also includes the loss of a feature, such as deglottalization, where glottalization or ejective articulation is lost (e.g., [kʼ] or [kˀ] > [k]). In some cases, lenition may skip one of the sound changes; for example, a change from voiceless stop to fricative is more common than the series voiceless stop > affricate > fricative.

**Opening**

In the opening type, the articulation becomes more open with each step. Opening lenition involves several changes: shortening of double consonants, affrication of stops, spirantization or assibilation of stops or affricates, debuccalization, and finally elision. Examples include [tt] or [tː] > [t] (shortening, as in Greek); [t] > [ts] (affrication, as in Latin *terra* to Aromanian *tsarã*); [t] or [ts] > [s] (spirantization, as in Gilbertese); [t̚] > [ʔ] or [s] > [h] (debuccalization, as in English or Spanish); and [t], [ts], [s], [ʔ], [h] > ∅ (elision, as in Old French *feste* to French *fête*).

**Sonorization**

The sonorization type involves voicing. It includes voicing, approximation, and vocalization. Examples are [t] > [d] (voicing, as in Korean); [d] > [ð] (approximation, as in Spanish); and [d] > [i] (vocalization). Sonorizing lenition occurs especially often between vowels (intervocalically), where it can be seen as a type of assimilation to the surrounding vowels, gradually eliminating features like obstruction or voicelessness that are not present in the vowels. Some sounds generated by lenition are later "normalized" into more common sounds, such as [b] → [β] → [v] or [d] → [ð] → [z]. In other cases, sounds are lenited and normalized at the same time, like direct changes [b] → [v] or [d] → [z].

**Vocalization**

L-vocalization is a subtype of sonorization. It can result in either a velar approximant or back vowel, or a palatal approximant or front vowel. In French, l-vocalization of the sequence /al/ produced the diphthong /au/, which was later monophthongized to /o/ in Modern French.

**Mixed**

Sometimes lenition mixes the opening and sonorization pathways. For example, [kʰ] may spirantize to [x] (opening), then voice to [ɣ] (sonorization). Lenition can be seen in Canadian and American English, where /t/ and /d/ soften to a tap [ɾ] (flapping) when not in initial position and followed by an unstressed vowel, so both *rate* and *raid* plus the suffix *-er* are pronounced [ˈɹeɪ̯ɾɚ]. In Central and Southern Italian, a common lenition 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* is normally pronounced [luˈʃaːno]. In Tuscany, /d͡ʒ/ likewise becomes [ʒ] between vowels.