 Suppose now that you and I are talking, and not far in the distance are Elwood and Ambrose. Elwood is clearly standing; it’s not so clear whether Ambrose is standing or sitting. I point to Ambrose and say, “that man is sitting.” Given that I am pointing to Ambrose, my statement will be true only if he is sitting, and so perhaps you change your beliefs accordingly; what was not part of the common ground, that Ambrose was sitting, now becomes part of the common ground.