Now I feel that the entire book is essentially there, in my head, and just needs to be written down. Writing will be essentially taking dictation.
Of course, this is illusory. The book will change shape several more times. I will come up with new ideas and the relation between existing ideas will shift. In this sense, my idea that I should be able to complete the book in a few days--and could given enough caffeine and research assistants--is inaccurate. The book needs that long germination process to be what it needs to be.
At the same time, having the book there, even in an illusory sense, is wonderfully comforting.