Abstract:

We propose a solution to the problem of logical omniscience in what we take to be its fundamental version: as concerning arbitrary agents – agents who can, on occasion, be logically quite dumb – and the knowledge attitude per se – as opposed to derivative attitudes, like ‘following from what one knows’. Our logic of knowledge is a spin-off from a general theory of thick content. The content of a sentence has two components: (i) an intension, taking care of truth conditions; and (ii) a topic, taking care of subject matter. We present a list of plausible logical validities and invalidities for the logic of knowledge and isolate three explanatory factors for them: (1) the topic-sensitivity of content; (2) the fragmentation of knowledge states; (3) the defeasibility of knowledge acquisition. We then present a dynamic epistemic logic that yields precisely the desired validities and invalidities.