 In response to these objections, analytic functionalists contend, as they did with the inverted and absent qualia objections, that sufficient attention to what is required for a creature to duplicate our functional organization would reveal that zombies are not really conceivable, and thus there is no threat to functionalism and no explanatory gap. A related suggestion is that, while zombies may now seem conceivable, we will eventually find them inconceivable, given the growth of empirical knowledge, just as we now find it inconceivable that there could be H2O without water (Yablo 1999). Alternatively, some suggest that the inconceivability of zombies awaits the development of new concepts that can provide a link between our current phenomenal and physical concepts (Nagel 1975, 2000), while others (McGinn 1989) agree, but deny that humans are capable of forming such concepts. 