  In perhaps its weakest form, it asserts a practical limit on our present explanatory abilities; given our current theories and models we can not now articulate an intelligible link. A stronger version makes an in principle claim about our human capacities and thus asserts that given our human cognitive limits we will never be able to bridge the gap. To us, or creatures cognitively like us, it must remain a residual mystery (McGinn 1991). Colin McGinn (1995) has argued that given the inherently spatial nature of both our human perceptual concepts and the scientific concepts we derive from them, we humans are not conceptually suited for understanding the nature of the psychophysical link. Facts about that link are as cognitively closed to us as are facts about multiplication or square roots to armadillos. They do not fall within our conceptual and cognitive repertoire. An even stronger version of the gap claim removes the restriction to our cognitive nature and denies in principle that the gap can be closed by any cognitive agents.