by Mark Kleiman
While "thee" and "thou" (and the corresponding verb forms such as "shalt") sound formal to us because they're associated with the Bible, they were originally the informal or intimate versions of of the second person pronoun, used either with kin and close friends or from superior to inferior.
But we can carry the analysis back one more step. Before "thee" (French "tu," German "du") was informal or intimate, it was singular, while "you" and its equivalents were plural.
At some point, addressing a singular interlocutor in the second person plural became the formal or honorific form. (The connection of plurality with honor is maintained in the royal "we.") Over time, the honorific plural became the normal polite form of address, and the singular was reserved for intimates and inferiors.
That had the unfortunate effect of eliminating the distinction between the singular and plural forms of the second person. In the sentence "I'm coming to see you" it's clear that there's only one of me (else it would be "We're coming...") but unclear whether I'm coming to see you as an individual or a group of which you are one. (The Southern regional "you-all/y'all" filled in this gap neatly, but failed to achieve standard status.)
Of course, the pressing need in English today is not for a second-person singular but for a neuter third-person singular, to avoid the clumsy "his or her" formulations. On this point, the demos has spoken, adopting the plural they/them/their in place of the neuter singular. Someone just suggested replacing the motto of the Reality Based Community, "Everyone is entitled to his own opinion, but not his own facts," with "their own opinion," etc. I refused, partly because the motto is a quotation from Pat Moynihan, who is no longer around to consent to the change, but more because I'm an old prescriptivist fuddy-duddy and the use of plural for singular sounds illiterate to my aging ear.
The Quaker "thee" sounds archaic (and has now largely passed out of use), but when it was first adopted the informal/intimate second-person forms were still in active use.
The Quaker objection to the formal "you" was, as I understand it, two-fold. First, like removing one's hat in the presence of superiors, it reflected what George Fox and his followers thought an inappropriate distinction among the social ranks, tending to blur what seemed to them the obvious fact that we are all equally the Children of God. Second, because the polite "you" was originally a plural form, using it for a singular indivual seemed to the early Friends a departure from strict veracity, on which they placed a high value.
For reasons I don't understand, but perhaps connected with their belief in simplicity, the Quakers then simplified matters by using "thee" as the nominative as well as the accusative/objective cases: "Thee is," in Quaker-speak, not "Thou art."
I hope, Friend Reader, that thou hast clearly grasped these subtle distinctions. If not, and thou wilt email me, I will attempt to clarify it for thee.