 An early line of defense against these arguments, endorsed primarily but not exclusively by a priori functionalists, is known as the “Ability Hypothesis”. (Nemirow 1990, 2007, Lewis 1990, Levin 1986). “Ability” theorists suggest that knowing what it's like to see red or feel pain is merely a sort of practical knowledge, a “knowing how” (to imagine, remember, or re-identify, a certain type of experience) rather than a knowledge of propositions or facts. (See Tye 2000, for a summary of the pros and cons of this position; for further discussion, see the essays in Ludlow, Nagasawa, and Stoljar 2004.) An alternative view among contemporary functionalists is that coming to know what it's like to see red or feel pain is indeed to acquire propositional knowledge uniquely afforded by experience, expressed in terms of first-personal concepts of those experiences. But, the argument continues, this provides no problem for functionalism (or physicalism), since these special first-personal concepts need not denote, or introduce as “modes of presentation”, any irreducibly qualitative properties. This view, of course, shares the strengths and weaknesses of the analogous response to the conceivability arguments discussed above. If it is plausible, however, it can also challenge the argument of some philosophers (e.g., Chalmers, 2002, Stoljar, 2001, and Alter, 2016) that maintains that no physicalistic theory, not even fundamental physics, can provide anything but a relational characterization of the items in their domains—their structure and dynamics—and concludes that no physicalistic theory can capture what seems, from the inside, to be the intrinsic, non-relational properties of our experiential states. (See the essays in Alter and Nagasawa, 2015, Part III, for further discussion.) 