Inexpressible Ignorance

Sometimes, ignorance is inexpressible. Lewis (2009) recognized this when he argued that we cannot know which property occupies which causal role. As he put it, ‘we cannot answer the question: which property occupies that role? But worse: not only can we not answer that question, we can’t even ask it ’ (p. 215-6). This peculiar state of ignorance arises in a number of other domains too, including ignorance about our position in space and the identities of individuals. In all these cases we are ignorant in a way that we cannot express. What exactly is inexpressible ignorance? It is not hard to give an ini-tial characterization of the phenomenon (section 1). The hard question is what it really consists in, for I will argue that on many standard models of ignorance there is nothing it could consist in (section 2). In particular, in cases of inexpressible ignorance we arguably know all the propositions or facts there are to know about the domain, in which case the ignorance cannot be assimilated to ordinary cases of not knowing a proposition o