[alberto_ol]

I thought that Thou was informal, froma wikipedia "For a long time, however, thou remained the most common form for addressing an inferior person"

https://en.wikipedia.org/wiki/Thou#History

Also in etymonline "By c. 1450 the use of thou to address inferiors gave it a tinge of insult"

https://www.etymonline.com/search?q=Thou