  Martin notes an objection that this comparison with sight might give rise to. When two objects are impersonally indiscriminible through sight, we tend to think that the objects in question must share a property—an appearance—that is detectible through vision. The fact that two visible objects cannot be told apart by sight suggests that there is something in common between them that sight does detect. So we might also think that if two experiences are introspectively indiscriminible, these experiences must share a property—a phenomenal property—that introspection is tracking. Martin’s response to this objection is to reject a model of introspection that he thinks lies behind it. Martin suggests that in a case in which two objects are impersonally visually indiscriminible, we are led to posit a common appearance the objects share that vision can discern, because we think of sight as a mode of coming to be aware of a realm independent of it. So, according to Martin, the same story will apply to the case of introspection only if we suppose that when one introspects the phenomenal character of one’s experience one is detecting features of some realm that is independent of one’s introspective access to it. Martin argues that if one adopts this model of introspection then one will either have to allow that it is possible for one’s experience to have a real phenomenal nature rather different from the one it introspectively seems to have, which remains inaccessible to introspection, or one will have to accept that introspection involves the use of a “super-mechanism”, which tracks the phenomenal character of one’s experience in a such a way that it cannot fail, or can only fail when it is knowable that it has.