The major theory of consciousness propounded by the earlier generation of physicalists – such as J. J. C. Smart and D. M. Armstrong was that our knowledge of our conscious states was topic neutral – that is, we recognize them only by their relations of similarity and dissimilarity to each other and by the contexts in which they usually occur. I argue in this chapter for two claims. First, that this deployment of topic neutrality seems inevitable for any form of physicalism that allows that sensations (and the like) are occurrent physical states: for we are certainly not aware of them under any of their physical features. Despite this pressure, almost no later physicalists explicitly adopt this strategy, but we see, as the book progresses, they often approach to it indirectly..Second, that the knowledge argument refutes topic neutrality, because if Mary knows all the relevant physical facts, there is nothing left for her to gain when she gets ‘neutral’ knowledge by experience. I then introduce the knowledge argument in some detail and consider the various strategies that might be used against it, and indicate in which of the following chapters these will be discussed.