 On one version of this view, phenomenal concepts are just indexical concepts applied to phenomenal states via introspection (see Lycan 1996). On an alternative version of the view, phenomenal concepts are very special, first-person concepts different in kind from all others (see Tye 2003). This response to the explanatory gap obviously bears affinities to the second physicalist response sketched in Section 3 to the Knowledge Argument. Unfortunately, if the appeal to phenomenal concepts by the physicalist is misguided, then it cannot be used to handle the gap.