I've put a new paper online: "Actuality and Knowability". This is a short paper with an argument from five antecedently plausible premises for the conclusion that there are instances of p iff actually p that are not knowable a priori, and indeed not knowable at all. (One takes p to be No-one entertains q, where q is a proposition no-one actually entertains.) This conclusion is surprising, at least to me, as the view that p iff actually p is always knowable a priori is more or less philosophical orthodoxy, and it is a view that I was strongly inclined to hold myself. It has some other surprising consequences. For example, it suggests that knowability is not closed under a priori entailment, and that provability does not entail knowability.
In the paper, I offer a diagnosis of the result in terms of the phenomenon I call "semantic fragility", and I explore some options for accepting or avoiding the result. I also draw some tentative morals. For now, I'm inclined to think that some possible morals are (i) that a scope analysis of 'actually' has more going for it than one might antecedently have thought, (ii) that the epistemological properties of sentences and of the propositions they express can come apart in surprising ways, and (iii) that a notion of propositional apriority along the lines of There is an a priori justification for p is in some ways runs deeper than the standard It is knowable a priori that p.
The seed for the paper was a remark near the end of my 2006 reply to Soames. The argument poses obvious problems for Soames's view of 'actually' (discussed briefly in the current paper), but I've come to think that the underlying phenomenon is of broader relevance. I've been led to think about these matters further by working through issues about sentential and propositional apriority in Chapter 2 of Constructing the World (although I haven't yet incorporated this new material into the chapter) and in note 24 of "Propositions and Attitude Ascriptions: A Fregean Account". I suspect that I haven't yet gotten to the bottom of all this, and any thoughts are welcome.