You're right. I suppose I could have said the ``this'' sound versus the ``thin'' sound. ``This'' vibrates your vocal cords, which means voiced, and ``thin'' doesn't, which means non-voiced (or voiceless). It's the same difference as between English ``V'' and English ``F''.

I'm sure you meant ``plural'' and not ``3rd person'', by the way. German, from which English directly evolved, actually has only one word to mean both singlular and plural second person, as well, ``Sie''. On the other hand, informal German has two separate words, ``du'' and ``ihr''. Then again, I know little about historical German.

While doing a little bit of research about German pronouns just now (my German is very rusty), I came across a paper about the Development of the Second-Person Pronoun, and it claims that ``thou'' and ``ye'' (not the same as the mispronounced article ``ye/the'') were singular and plural during Middle English. It's an interesting read, if you care at all about this stuff. Contradicts some of what I said earlier; they're probably right, as I'm not a professional scholar.