"The SF approach: an awareness that things could have been different, that this is one of many possible worlds, that if you came to this world from some other planet, this would be a science fiction world."
- Neal Stephenson

The history of tests to distinguish human beings from machines is short, but interesting. Alan Turing devised what is commonly known as the Turing Test; the crux of the test is language usage.

It is intriguing to note that Dick has vacated the field from the standpoint of trying to defend human intelligence versus machine intelligence; he relies on emotional response. Biometric data are also used to authenticate the person being tested. At the time the novel was written, computers were able to play chess, but poorly. (Turing himself wrote the first chess program in 1950, using a limited size board and fewer pieces. Claude Shannon published the first article on the subject, outlining how a computer would evaluate and choose positions. Chess programs reached Grand Master status by 1988.)