For what is known as Transphonologization?

In historical linguistics, transphonologization (also known as rephonologization or cheshirization, see below) is a type of sound change whereby a phonemic contrast that used to involve a certain feature X evolves in such a way that the contrast is preserved, yet becomes associated with a different feature Y.

For example, a language contrasting two words */sat/ vs. */san/ may evolve historically so that final consonants are dropped, yet the modern language preserves the contrast through the nature of the vowel, as in a pair /sa/ vs. /sã/. Such a situation would be described by saying that a former contrast between oral and nasal consonants has been transphonologized into a contrast between oral and nasal vowels.

The term transphonologization was coined by André-Georges Haudricourt. The concept was defined and amply illustrated by Hagège & Haudricourt; it has been mentioned by several followers of panchronic phonology, and beyond.