A correspondent from Armenia writes to ask about the origins of you know as a parenthetical conversational 'filler'. Is it recent?
No. The Oxford English Dictionary has citations from the 14th century - though it isn't always clear whether the words are being used parenthetically or with their full meaning. I've just had a look at Shakespeare's usage (by typing 'you know' into the Glossary box at www.shakespeareswords.com) and found several apparently parenthetical instances, but the meaning isn't always clear. Which is it, when the Countess says 'You know, Helen, I am a mother to you' (All's Well, 1.3.133)? But it's clearly a filler when Falstaff says 'to serve bravely is to come halting off, you know' (2H4. 2.4.49). So the usage has definitely been around for a long time, and probably evolved as a weakening of the literal meaning, in contexts such as the one used by the Countess.