 There are different responses to the hard problem. One response is to sharpen the explanatory targets of neuroscience by focusing on what Chalmers calls structural features of phenomenal consciousness, such as the spatial structure of visual experience, or on the contents of phenomenal consciousness. When we assess explanations of specific contents of consciousness, these focus on the neural representations that fix conscious contents. These explanations leave open exactly what the secret ingredient is that shifts a state with that content from unconsciousness to consciousness. On ingredients explaining generic consciousness, a variety of options have been proposed (see  section 3),  but it is unclear whether these answer the Hard Problem, especially if any answer to that the Problem has a necessary condition that the explanation must conceptually close off certain possibilities, say the possibility that the ingredient could be added yet consciousness not ignite as in a zombie, a creature without phenomenal consciousness (see the entry on  zombies).  Indeed, some philosophers deny the hard problem (see Dennett 2018 for a recent statement). Patricia Churchland urges: “Learn the science, do the science, and see what happens” (Churchland 1996: 408).