I recently wrote an essay on the book. The main theme of the book (and all of Dick's works), is that there *cannot* be one base reality experienced by everyone. Every person's reality is equally valid as they experience it.
Running throughout the book is Deckard's questioning of his own humanity and a strange duality; Chaos and order/life and death/human or synthetic/ real or unreal - also please look into the 'phantom twin' motif explored in many of his works; he was born with a twin sister who dies shortly after birth; this loss haunted his works
In one chapter Deckard is arrested by a cop who claims he has no record of Deckard on file as a registered blade runner. He takes him to a parallel police HQ, which turns out to be run entirely by androids, with a human blade runner working (the only blade runner and human in the department). Therefore with these themes of duality/mirror realities it is strongly suggested that it is entirely possible that Deckard is in fact a replicant himself, albeit one with implanted memories to make him think he is human. - He may well be the only <i>replicant</i> working in a department full of humans! It all depends on whose viewpoint you choose to take.
-- see also 'Impostor' and 'A Scanner Darkly' for more extreme examples of this same running theme in Dick's work.
Androids are indeed illegal on earth, however; Rachael is living legally on earth as she is technically the property of the Rosen Association. As a programmed android working for the police department (or maybe also for the Rosen association to clear up the mess and bad publicity caused by some of their creations running amok), Deckard would also then technically be allowed on earth.
The book strongly implies that Rick may or may not be synthetic, but is strongly ambiguous. This is to emphasize the point that reality is totally subjective. The film isn't nearly as confrontational in this respect, although the final cut does do more justice to the book in this respect.
Anyway I am producing a series of illustrations for the book (4 plus cover) based around the themes stated earlier; Chaos and order/life and death/human or synthetic/ real or unreal, and would really appreciate anybodies feedback and especially suggestions on where I could take this or suggested passages from the book.
- Look forward to some input guys