One of Philip K. Dick’s recurring themes figures prominently in Do Androids Dream of Electric Sheep? This theme is identified in Dick’s 1978 lecture, “How to Build a Universe That Doesn’t Fall Apart Two Days Later,” collected in The Shifting Realities of Philip K. Dick: Selected Literary and Philosophical Writings (1995), edited by Lawrence Sutin. In that lecture, Dick observes that throughout his career he has been preoccupied with the question, “What constitutes the authentic human being?” Dick often explores this question in novels and stories featuring androids or other constructs closely resembling human beings. These include the novels The Simulacra (1964) and We Can Build You (1972) and stories such as “The Electric Ant” (1969).

In Do Androids Dream of Electric Sheep?, Dick imagines a near future in which successive generations of androids become ever more sophisticated in their mimicry of humans. The model that Deckard must retire, the Nexus-6, is the most advanced yet. There remains one crucial difference between humans and androids: empathy. Androids can learn to mimic human concern, but they do not genuinely feel empathy for other creatures. Deckard employs a psychological/physiological test, the Voigt-Kampff Altered Scale, that detects the absence of empathy in the microseconds before it can be faked.

This emphasis on empathy as the defining human characteristic runs throughout the novel. It is poignantly embodied in the “chickenhead” John Isidore (“chickenhead” being a derogatory term for humans who, as a result of the fallout, lack normal intellectual capacities). Isidore innocently befriends three of the fugitive andys, then watches in horror as they gratuitously cut the legs off a spider. Empathy also is at the core of the quasi-religious movement known as Mercerism, in which both Deckard and Iran participate. So intense is the identification experienced by communicants in “fusion” with the archetypal figure of Wilbur Mercer that they sometimes emerge from a session with wounds inflicted by rocks thrown at Mercer, rather like Christian saints who receive the stigmata.

Dick’s characters, however, are far from sainthood. The most important lesson Deckard learns in his long day is imparted to him in a revelation from Mercer. Deckard, appalled by the killing, wonders if he can finish the job. He explains later to Iran, “Mercer said it was wrong but I should do it anyhow.” As a character recognizes in another Dick novel, The Man in the High Castle (1962), “There is evil! . . . It’s an ingredient in us. In the world.” Acknowledging that, one does the best one can.

Many people know the story of Do Androids Dream of Electric Sheep? not from the novel itself but from the film based on it, Blade Runner (1982). The film departs from the book in many ways, most conspicuously in its treatment of the protagonist. Dick’s Deckard is a bounty hunter but also a husband. In the film, Deckard (played by Harrison Ford) is a loner, a futuristic private eye. Dick’s final message is a modest affirmation of human virtues; the film’s conclusion is both cynical and romanticized, showing Deckard with the beautiful android. As for empathy, that theme is turned upside down: Mercerism disappears from the story altogether, and Deckard survives only because the leader of the androids (or “replicants,” as they are called in the film), his mortal foe, shows compassion for him.