The Emperor's New Mind by Roger Penrose
After scanning the host of negative reviews of this book, I feel compelled to speak my piece. I've read this book more than once, and often return to it and find a few more nuggets. It seems to me that there are few other books that grapple as honestly with the nature of consciousness.
The AI community, and materialist scientists who start with the premise that --- it's all in the brain; we don't know how or where but one day we will know, are the people that Penrose challenges. This book predictably annoys them.
Since the book's publication in 1989, when Penrose asserted that the nature of consciousness will not be explained in materialistic terms, his prediction has proved true. We're no closer to understanding consciousness than we were then. Perhaps, as Penrose suggests, we're like scientists trying to build a perpetual motion machine, who still don't accept the second law of thermodynamics, stating that such a machine cannot be built.
It's a blow to our human hubris when a scientist makes a proposition that begins with the words: "It is not possible..." Using arguments based on Godel's theorem of incompleteness, and the work of Turing, Penrose makes a credible case for why consciousness will never be explained in materialistic terms. In so doing he steps on a lot of toes.
But maybe he's right. 2 plus 2 will never be 5 either.