This article discusses the problems and difficulties, the results so far, and some improvements in logic and logical languages that may be required to formalize common sense. Fundamental conceptual advances are almost certainly required. The object of the paper is to get more help for AI from philosophical logicians. Some of the requested help will be mostly philosophical and some will be logical. Likewise the concrete AI approach may fertilize philosophical logic as physics has repeatedly fertilized mathematics.

Abstract Three key ways of updating one’s knowledge are (i) perception of states of affairs, e.g., seeing with one’s own eyes that something is the case, (ii) reception of messages, e.g., being told that something is the case, and (iii) drawing new conclusions from known facts. If one represents knowledge by means of Kripke models, the implicit assumption is that drawing conclusions is immediate. This assumption of logical omniscience is a useful abstraction. It leaves the distinction between (i) and (ii) to be accounted for. In current versions of Update Logic (Dynamic Epistemic Logic, Logic of Communication and Change) perception and message reception are not distinguished. This paper proposes an extension of Update Logic that makes this distinction explicit. The logic deals with three kinds of updates: announcements, changes of the world, and observations about the world in the presence of witnesses. The resulting logic is shown to be complete by means of a reduction to epistemic propositional dynamic logic by a well-known method. 1.1 The Riddle of the Caps ‘I see nobody on the road, ’ said Alice. ‘I only wish I had such eyes, ’ the King remarked in a fretful tone. ‘To be able to see Nobody! And at that distance too!’ Lewis Carroll, Alice in Wonderland. We start with a variation on the so-called ‘wise men puzzle ’ [24]. Imagine four people standing in line, with three of them looking to the left, and one looking to the right. These fellows, let us call them 1,2,3,4, each wear a cap. The leftmost guy,