Palatalization is sometimes an example of assimilation. In some cases, it is triggered by a palatal or palatalized consonant or front vowel, but in other cases, it is not conditioned in any way.
Palatalization changes place of articulation or manner of articulation of consonants. It may add palatal secondary articulation or change primary articulation from velar to palatal or alveolar, alveolar to postalveolar.
It may also cause a consonant to change its manner of articulation from stop to affricate or fricative. The change in the manner of articulation is a form of lenition. However, the lenition is frequently accompanied by a change in place of articulation.
Palatalization of velar consonants commonly causes them to front, and apical and coronal consonants are usually raised. In the process, stop consonants are often spirantised except for palatalized labials.
Palatalization, as a sound change, is usually triggered only by mid and close (high) front vowels and the semivowel [j]. The sound that results from palatalization may vary from language to language. For example, palatalization of [t] may produce [tʲ], [tʃ], [tɕ], [tsʲ], [ts], etc. A change from [t] to [tʃ] may pass through [tʲ] as an intermediate state, but there is no requirement for that to happen.
In some Zoque languages, [j] does not palatalize velar consonants but it turns alveolars into palato-alveolars. In the Nupe language, /s/ and /z/ are palatalized both before front vowels and /j/, while velars are only palatalized before front vowels. In Ciluba, /j/ palatalizes only a preceding /t/, /s/, /l/ or /n/. In some variants of Ojibwe, velars are palatalized before /j/, but apicals are not. In Indo-Aryan languages, dentals and /r/ are palatalized when occurring in clusters before /j/, but velars are not.
Palatalization sometimes refers to vowel shifts, the fronting of a back vowel or raising of a front vowel. The shifts are sometimes triggered by a nearby palatal or palatalized consonant or by a high front vowel. The Germanic umlaut is a famous example.
A similar change is reconstructed in the history of Old French in which Bartsch's law turned open vowels into [e] or [ɛ] after a palatalized velar consonant. If it was true for all open vowels in Old French, it would explain the palatalization of velar plosives before /a/.
In Erzya, a Uralic language, the open vowel [a] is raised to near-open [æ] after a palatalized consonant, as in the name of the language, [erzʲæ].
In Russian, the back vowels /u o/ are fronted to central [ʉ ɵ], and the open vowel /a/ is raised to near-open [æ], near palatalized consonants. The palatalized consonants also factor in how unstressed vowels are reduced.
Palatalization is sometimes unconditioned or spontaneous, not triggered by a palatal or palatalized consonant or front vowel.
In southwestern Romance, clusters of a voiceless obstruent with /l/ were palatalized once or twice. This first palatalization was unconditioned. It resulted in a cluster with a palatal lateral [ʎ], a palatal lateral on its own, or a cluster with a palatal approximant [j]. In a second palatalization, the /k/ was affricated to [tʃ] or spirantized to [ʃ].
- > Istriot ciamà /tʃaˈma/, Portuguese chamar /ʃɐˈmaɾ/
In the Western Romance languages, Latin [kt] was palatalized once or twice. The first palatalization was unconditioned: the /k/ was vocalized to [i̯t] or spirantized to [çt]. In a second palatalization, the /t/ was affricated to [tʃ]:
- > Spanish noche, western Occitan nuèch, Romansh notg
In many dialects of English, the back vowel /uː/ is fronted to near-back [u̟ː], central [ʉː], or front [yː]. This vowel shift is unconditioned, happening in all cases, and not triggered by another sound.
A similar change is reconstructed for Ancient Greek. In the Attic dialect before the Classical period, the back vowels /u uː/ were fronted to [y yː]. During the Koine or Medieval Greek period, they were unrounded to [i iː], and they finally merged as short [i], the pronunciation that they have in Modern Greek.
Anticipatory and progressive
When palatalization is assimilatory or triggered by a consonant or vowel, it is triggered by a following sound (anticipatory) or by a preceding sound (progressive).