 However, primary possibility is no less “real” than secondary possibility. Chalmers argues that there is only one space of worlds or that “conceptual=logical=metaphysical possibility (at the level of worlds)” (1999: 478). This is what he calls “Modal Monism”. What varies, within modal space, is not the kind of worlds we are considering (namely “merely” logically-conceptually possible versus “genuinely” metaphysically possible); but rather the truth-values of the expressions under examination at a given world, depending on whether we consider their primary or secondary intensions. Because of Modal Monism, within Chalmers’ framework every primary possibility is thus a metaphysical possibility, though it might not be a secondary possibility. “Water is not H2O” is ideally positively primarily conceivable, and therefore primary possible. Given Modal Monism, Chalmers can thus argue that “water is not H2O” is a metaphysical possibility, while also resisting the challenge posed by the Kripkean a posteriori necessities. For “water is not H2O” is a primary possibility but not a secondary possibility, given that “water” actually picks out H2O.