Why did Roy let Deckard live?

One of the main themes of the movie is the question, what makes us human and especially, if the replicants in their desperate struggle for survival are in the end not more human than the cold blooded killing Blade Runner. In this way this scene may be interpreted as Roy showing a humanitiy, Deckard would have probably not shown to him.

And I also think Roy actually already saw his end coming at this point. So he just let matters rest and helped him, to tell him his last words, since he had not to fear him anymore. He was only fighting for his own survival and showed his humanity when laying down his sword once this obstacle didn't stand between them anymore.

Roy and the other replicants have been engaged in a desperate struggle to live, and Roy has been running most of the show. The struggle was Roy's and though it has been carried out on the cerebral level where he is the most able (i.e. get to Earth, find Tyrel, get access, force him to provide a fix...) it has been a desperate time nonetheless.

When he finds Pris dead, Roy is understandable angry and he starts by trying to make Deckard live the fear and desperation, but in the course of watching (and causing) Deckard's struggles he begins to empathize with the man who came after him.

On top of all that, Roy's end is coming. His body is breaking down during the same time as Deckard fights to stay ahead of him, Roy's final speech gives us a clue: he wants someone to remember that he lived and some pale shadow of what he saw.

Empathy and legacy come together and Deckard gets his reprieve.

atleast someone recognise that he was trying to be a mere human trying to survive

Roy and the other replicants have not been shown to be a 'violent' variety. It is only when they realise the impending doom carried by their bodies that they become * rebellious* and decide to gain life at any cost. When Roy learns from his maker that there is possibly no cure, he kills him in his rage. As he is being chased by Deckard, Roy's impulse is to survive and defend himself from being terminated. However, after losing his alies, Roy comes to a realization and understanding of the inevitability of his death. It is because of this, that Roy wishes to die like humans and not like a machine being put out of work. Knowing of his fast approaching death, regardless of whatever he does, Roy decides that atleast someone recognise him in his dying hours that he too was trying to be a mere human trying to survive. It is for this reason he chose to say those words to Deckard and let him live. Or rather, refused to kill him by his own choise.

This is a difficult philosophical question.

We, the audience, are asked to judge Roy's motivations from observing his actions. And the fact that there are so many differing versions of this movie makes this a somewhat more than usually difficult thing to do.

Nevertheless, my opinion is that Roy, and the other replicants, long to be human. It seems to me that Ridley Scott is telling us that they are not merely struggling to gain more life, but are actually seeking a way to become fully human; something which, of course, includes a longer lifespan.

My take on Roy is that in saving Deckard's life he is demonstrating to the audience that he is psychologically already human, in that he is acting in the way a human would act.

Whether Deckard, who in one edit subsequently kills Roy, is morally justified in doing so - since he owes Roy a debt for saving his life - is a different question. Subtly, Ridley Scott is implying here that Deckard is less human than Roy, to support the theme Scott is fostering that Deckard is actually a replicant.

Thus, Roy lets Deckard live in order to demonstrate that Roy is thinking and behaving like a human; and, in addition, to contrast this with Deckard then killing Roy, thereby showing himself to be less human than Roy.

In the original theatrical cut of Blade Runner (the one with Deckard's narration) he speculates:

"I don't know why he saved my life. Maybe in those last moments he loved life more than he ever had before. Not just his life - anybody's life; my life. All he'd wanted were the same answers the rest of us want. Where did I come from? Where am I going? How long have I got? All I could do was sit there and watch him die."

To mess with him, so the man that was hunting replicants can owe his life to one, and then to give him a little speech about the bitterness of death.

Roy was pretty boss all in all