Draft version, Comments welcome!"The collapsing of Strawson's sleeping children into Stalnaker and Saddock's lunch obviating sister, who herself metamorphoses into Grice's aunt's philharmonic cousin who in turn mutates into Burton-Roberts' lunch-going sister should remind us that in the evolution of presupposition theory, all progress is relative."-Horn 1990:487 * To appear in Daniel Altshuler (ed.), Linguistics Meets Philosophy, Cambridge University Press. Thanks to Daniel Altshuler for very helpful comments.1 I am assuming solitary has a double meaning in this context: The sole (only) neighbour and also that this neighbour is solitary.