Some contemporary discussion about the explanation of consciousness substantially recapitulates a decisive debate about reference, knowledge and justification from an earlier stage of the analytic tradition.  In particular, I argue that proponents of a recently popular strategy for accounting for an explanatory gap between physical and phenomenal facts – the so-called “phenomenal concept strategy” – face a problem that was originally fiercely debated between Schlick, Carnap, and Neurath.  The question that is common to both the older and the contemporary discussion is that of how the presence or presentation of phenomenal experiences can play a role in justifying beliefs or judgments about them.  This problem is, moreover, the same as what was classically discussed as the problem of acquaintance.  Interestingly, both physicalist and non-physicalist proponents of the phenomenal concept strategy today face this problem.  I consider briefly some recent attempts to solve it and conclude that, although it is prima facie very plausible that acquaintance exists, we have, as yet, no good account of it.