The nature of epistemic space

There are many ways things might be, for all I know. For all I know, it might be that there is life on Jupiter, and it might be that there is not. It might be that Australia will win the next Ashes series, and it might be that they will not. It might be that my great-grandfather was my great-grandmother’s second cousin, and it might be that he was not. It might be that brass is a compound, and it might be that it is not. There are even more ways things might be, for all I know with certainty. It might be that there are three chairs in this room, and it might be that there are not. It might be that water is H2O, and it might be that it is not. It might be that my father was born in Egypt, and it might be that he was not. It might be that I have a body, and it might be that I do not. We normally say that it is epistemically possible for a subject that p, when it might be that p for all the subject knows. So it is epistemically possible for me that there is life on Jupiter, or that brass is a compound. One can define various different standards of epistemic possibility, corresponding to various different standards for knowledge. For example, one might say that it is epistemically possible in the Cartesian sense (for a subject) that p when it might be that p, for all 1Published in Epistemic Modality, edited by Andy Egan and Brian Weatherson (Oxford University Press, 2011). The original version of this paper (lacking sections 6-9 and with a longer section on applications) was put online in April 2001. Because that version has attracted published responses (e.g. Jago 2009 and Whittle 2009) and because it contains some relevant material not included here, I have left it online a