Sagan offers a lengthy explanation of how the scientific method works, and how it is demonstrably more successful than any of its pseudoscientific imitators. He teaches the importance of having a skeptical worldview, especially of extraordinary claims. As he stated in Cosmos, “Extraordinary claims require extraordinary evidence.” Sagan explains the necessity of Ockham’s Razor – the rule of thumb that people should not assume anything that the evidence does not require them to assume – in critical thought. He systematically exposes the absurdity behind many of the most popular modern-day forms of pseudoscience, including astrology, homeopathy, psychics, alien abductions, Freudian psychoanalysis, doomsday predictions, graphology, and numerology.
While some have criticized the book as being anti-religious, Sagan himself disputed this characterization. He was clearly an agnostic, but had a deep appreciation for the sense of wonder that religion could inspire and recognized that it had much in common with his own appreciation for science. He does take certain religious views to task – such as the ideas of young-earth creationism, faith healing, and divine intervention. However, he notes that although “religions are often the state-protected nurseries of pseudoscience…there is no reason why religions have to play that role.” Sagan was a strong advocate of finding common ground between the religious and scientific communities: a central theme of his novel Contact.
14 years after its original publication, The Demon-Haunted World seems more topical than ever. The applications of critical thinking extend far beyond the realm of science. By being skeptical of unusual claims, we can better gauge the veracity of some of the odd statements we routinely hear from any authority, including our politicians, educators, corporate gurus, and religious leaders. In my opinion, there is no more important skill that our schools should teach students than the process of thinking critically. Unfortunately, most high schools and many universities don’t offer any classes in critical thought, even as electives. Carl Sagan’s The Demon-Haunted World can guide us where our schools do not.
The Demon-Haunted World was Sagan's last book before his death in 1996. Although it never reached the same level of popularity as some of his other works such as Cosmos and Contact, I think it is his most important work for the layperson. The Demon-Haunted World has shaped my view of the world more than any other book.