2585: Rhotacism in Latin 'esse' Jan 11, 2022

Rhotacism in Latin, a process in which [s] and [z] in Archaic Latin would develop into [r] in Classical Latin. This was not universal, and some lingering traces existed because of the oppositional phenomenon of zetacism. This led to the Archaic Latin verb 'esō' ('to be') having the 3rd infinitive form of 'esse' in Classical Latin, but the imperfect and future forms of the word all have a root with 'r', such as 3rd person future 'erit'.