Some philosophers consider that some of their colleagues deny that consciousness exists. We shall call the latter ‘deniers’, adopting a term that was initially meant pejoratively. What do the deniers deny? In order to answer this question, we shall examine arguments, both of some deniers and of their critics, and present denialism as a systematic highly non-trivial position that has had some interesting achievements. We will show that the denialist project concerns the epistemology of the mind and specifically of consciousness: (...) what can be known about it, and how it can be known. The main argument of denialism is that first-person reports about the mental realm are not always the best source of information about that realm, and are certainly not reliable. This leads the deniers to realize that the reference and meaning of mental terms as used in standard philosophical literature are vague and call for clarification, and that what many take to be empirical data in the study of the mind are actually heavily laden with theory. Denialism thus makes scientific and philosophical research clearer and more fruitful. (shrink)