https://en.wikipedia.org/wiki/T–V_distinction https://en.wikipedia.org/wiki/T–V_distinction has some extensive discussion. The version I heard is roughly that,

https://en.wikipedia.org/wiki/T–V_distinction https://en.wikipedia.org/wiki/T–V_distinction has some extensive discussion. The version I heard is roughly that, though I recall a professor blaming it on Cromwell's commonwealth rather than the Quakers (after the commonwealth fell thee/thou went completely out of favor.)