The philosophical literature on consciousness is quite unsystematic, with seemingly independent strands talking about related issues without making contact with each other. I have attempted to impose some structure on the sprawl by providing a unifying framework in which the various metaphysical and explanatory issues become clear. Much of the discussion in the literature can be translated into this framework without loss, and I hope the structure imposed by the framework brings out the deep relationships between a number of different issues. I find that discussions framed in terms of identity generally throw more confusion than light onto the key issues, and often allow the central difficulties to be evaded. By contrast, supervenience seems to provide an ideal framework within which the key issues can be addressed.
Modality is the key issue here.
Discussions that ignore this issue generally avoid the hardest questions about consciousness. Those skeptical of modal notions will be skeptical of my entire discussion, but I think there is no other satisfactory way to frame the issues. One of the delights of working on this book, for me, has come from the way the problem of consciousness has reached out to make contact with deep issues in many other areas of science and philosophy. But the scope and depth of the problem also make it humbling. I am acutely aware that at almost every point in this book there is more that could be said, and that in many places I have only scratched the surface.