Alan Alda: [in conversation about the social evolution of words] which reminds me of the singular "they," which everybody is needing to get a little more familiar with, and more accepting of. You say a very interesting thing about how some of us have trouble accepting that "they went into a store and had a soda," where we're talking about "Mary went into a store and had a soda," you're talking about one person. But originally - or a long time ago - we said "thee" and "thou" and changed it to "you," which is- which was plural, and we don't have a problem with my talking to you and calling you "you," I don't need to call you "thou." And I don't say, "you is," I say "you are."
Valerie Friedland: I think it's really funny because if we look back 300 years - which often we don't do, and that's why we hate the things we say today - we could find the same kinds of complaints about using you as we can find using singular they today. So grammarians like Robert Lowth and Lindley Murray would complain about how it was ungrammatical to use "you" as a singular. and not only that but most people don't realize that "you" is actually objective case and not nominative case, which means in plain English it's not meant to be used for subjects at all, it's supposed to be used for objects.
"Ye" is actually a subject case. So when you had a subject saying "you did this," it would be "ye did this." Not only did we move "you" to the subject position, we also started making what was once plural, singular. and then to top it off we started using plural verbs with it. All of this happened before any of us were born, so all of us do it without any problems today. Singular "they" is essentially the same sort of shift, pronouns have always changed over time - in fact "they" is not the original one in English either, it was brought it in by the Vikings -- so now it's just a matter of getting used to this grammatical shift, because a lot of the time in our grammar in our head we have it linked to being plural. And so it's just a matter of adjusting our knowledge to say " oh it's actually also singular." Now I can use a plural verb and it's going to be like "you," and take a plural verb whether I'm talking about one "they" or two "theys."