I've have always loved this greeting because I believe Emerson was trying to accomplish two different things with a single question. First, he was trying to challenge his friends to "think about their thinking" and assess their progress in this most critical field of life. I'd also like to believe that Emerson was expecting his friends would challenge his own thinking and, in the process, draw him closer to some undiscovered truth.
In this spirit, I'd then like to ask you the following question: What has become unclear to you since we last met? (And, if we haven't yet had the pleasure of meeting, let me just say that I look forward to meeting — and unlearning — from you.)