Although Blade Runner is ostensibly an action film, it operates on multiple dramatic and narrative levels. It is indebted to film noir conventions: the femme fatale; protagonist-narration (removed in later versions); dark and shadowy cinematography; and the questionable moral outlook of the hero – in this case, extended to include reflections upon the nature of his own humanity. It is a literate science fiction film, thematically enfolding the philosophy of religion and moral implications of human mastery of genetic engineering in the context of classical Greek drama and hubris. It also draws on Biblical images, such as Noah's flood, and literary sources, such as Frankenstein. Linguistically, the theme of mortality is subtly reiterated in the chess game between Roy and Tyrell, based on the famous Immortal Game of 1851, though Scott has said that was coincidental.
Blade Runner delves into the implications of technology on the environment and on society by reaching to the past, using literature, religious symbolism, classical dramatic themes, and film noir. This tension between past, present, and future is mirrored in the retrofitted future of Blade Runner, which is high-tech and gleaming in places but decayed and old elsewhere. Ridley Scott described the film as: "extremely dark, both literally and metaphorically, with an oddly masochistic feel", in an interview by Lynn Barber for the British Sunday newspaper The Observer in 2002. Scott "liked the idea of exploring pain" in the wake of his brother's skin cancer death: "When he was ill, I used to go and visit him in London, and that was really traumatic for me."
An aura of paranoia suffuses the film: corporate power looms large; the police seem omnipresent; vehicle and warning lights probe into buildings; and the consequences of huge biomedical power over the individual are explored – especially the consequences for replicants of their implanted memories. Control over the environment is depicted as taking place on a vast scale, hand in hand with the absence of any natural life, with artificial animals substituting for their extinct predecessors. This oppressive backdrop explains the frequently referenced migration of humans to extra-terrestrial ("off-world") colonies. The dystopian themes explored in Blade Runner are an early example of cyberpunk concepts expanding into film. Eyes are a recurring motif, as are manipulated images, calling into question reality and our ability to accurately perceive and remember it.
These thematic elements provide an atmosphere of uncertainty for Blade Runner 's central theme of examining humanity. In order to discover replicants, an empathy test is used, with a number of its questions focused on the treatment of animals – seemingly an essential indicator of someone's "humanity". The replicants appear to show compassion and concern for one another and are juxtaposed against human characters who lack empathy while the mass of humanity on the streets is cold and impersonal. The film goes so far as to put in doubt whether Deckard is human, and forces the audience to re-evaluate what it means to be human.
The question of whether Deckard is intended to be a human or a replicant has been an ongoing controversy since the film's release. Both Michael Deeley and Harrison Ford wanted Deckard to be human while Hampton Fancher preferred ambiguity. Ridley Scott has confirmed that in his vision Deckard is a replicant. Deckard's unicorn dream sequence, inserted into the Director's Cut, coinciding with Gaff's parting gift of an origami unicorn is seen by many as showing that Deckard is a replicant – as Gaff could have accessed Deckard's implanted memories. The interpretation that Deckard is a replicant is challenged by others who believe the unicorn imagery shows that the characters, whether human or replicant, share the same dreams and recognize their affinity, or that the absence of a decisive answer is crucial to the film's main theme. The inherent ambiguity and uncertainty of the film, as well as its textual richness, have permitted viewers to see it from their own perspectives.