Dawkins dedicates the book to Douglas Adams and quotes the novelist: "Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" The book contains ten chapters. The first few chapters make a case that there is almost certainly no God, while the rest discuss religion and morality.
Dawkins writes that The God Delusion contains four "consciousness-raising" messages:
- Atheists can be happy, balanced, moral, and intellectually fulfilled.
- Natural selection and similar scientific theories are superior to a "God hypothesis"—the illusion of intelligent design—in explaining the living world and the cosmos.
- Children should not be labelled by their parents' religion. Terms like "Catholic child" or "Muslim child" should make people cringe.
- Atheists should be proud, not apologetic, because atheism is evidence of a healthy, independent mind.
Chapter one, "A deeply religious non-believer", seeks to clarify the difference between what Dawkins terms "Einsteinian religion" and "supernatural religion". He notes that the former includes quasi-mystical and pantheistic references to God in the work of physicists like Albert Einstein and Stephen Hawking, and describes such pantheism as "sexed up atheism". Dawkins instead takes issue with the theism present in religions like Christianity, Islam, and Hinduism. The proposed existence of this interventionist God, which Dawkins calls the "God Hypothesis", becomes an important theme in the book. He maintains that the existence or non-existence of God is a scientific fact about the universe, which is discoverable in principle if not in practice.
Dawkins summarises the main philosophical arguments on God's existence, singling out the Argument from design for longer consideration. Dawkins concludes that evolution by natural selection can explain apparent design in nature.
He writes that one of the greatest challenges to the human intellect has been to explain "how the complex, improbable design in the universe arises", and suggests that there are two competing explanations:
- A hypothesis involving a designer, that is, a complex being to account for the complexity that we see.
- A hypothesis, with supporting theories, that explains how, from simple origins and principles, something more complex can emerge.
This is the basic set-up of his argument against the existence of God, the Ultimate Boeing 747 gambit, where he argues that the first attempt is self-refuting, and the second approach is the way forward.
At the end of chapter 4 ("Why there almost certainly is no God"), Dawkins sums up his argument and states, "The temptation [to attribute the appearance of design to actual design itself] is a false one, because the designer hypothesis immediately raises the larger problem of who designed the designer. The whole problem we started out with was the problem of explaining statistical improbability. It is obviously no solution to postulate something even more improbable". In addition, chapter 4 asserts that the alternative to the designer hypothesis is not chance, but natural selection.
Dawkins does not claim to disprove God with absolute certainty. Instead, he suggests as a general principle that simpler explanations are preferable (see Occam's razor), and that an omniscient or omnipotent God must be extremely complex. (Dawkins argues that it is logically impossible for a God to be simultaneously omniscient and omnipotent.) As such he argues that the theory of a universe without a God is preferable to the theory of a universe with a God.
Religion and morality
The second half of the book begins by exploring the roots of religion and seeking an explanation for its ubiquity across human cultures. Dawkins advocates the "theory of religion as an accidental by-product – a misfiring of something useful" as for example the mind's employment of intentional stance. Dawkins suggests that the theory of memes, and human susceptibility to religious memes in particular, can explain how religions might spread like "mind viruses" across societies.
He then turns to the subject of morality, maintaining that we do not need religion to be good. Instead, our morality has a Darwinian explanation: altruistic genes, selected through the process of evolution, give people natural empathy. He asks, "would you commit murder, rape or robbery if you knew that no God existed?" He argues that very few people would answer "yes", undermining the claim that religion is needed to make us behave morally. In support of this view, he surveys the history of morality, arguing that there is a moral Zeitgeist that continually evolves in society, generally progressing toward liberalism. As it progresses, this moral consensus influences how religious leaders interpret their holy writings. Thus, Dawkins states, morality does not originate from the Bible, rather our moral progress informs what part of the Bible Christians accept and what they now dismiss.
The God Delusion is not just a defence of atheism, but also goes on the offensive against religion. Dawkins sees religion as subverting science, fostering fanaticism, encouraging bigotry against homosexuals, and influencing society in other negative ways. Dawkins regards religion as a "divisive force" and as a "label for in-group/out-group enmity and vendetta".
He is most outraged about the teaching of religion in schools, which he considers to be an indoctrination process. He equates the religious teaching of children by parents and teachers in faith schools to a form of mental abuse. Dawkins considers the labels "Muslim child" or a "Catholic child" equally misapplied as the descriptions "Marxist child" or a "Tory child", as he wonders how a young child can be considered developed enough to have such independent views on the cosmos and humanity's place within it.
The book concludes with the question of whether religion, despite its alleged problems, fills a "much needed gap", giving consolation and inspiration to people who need it. According to Dawkins, these needs are much better filled by non-religious means such as philosophy and science. He suggests that an atheistic worldview is life-affirming in a way that religion, with its unsatisfying "answers" to life's mysteries, could never be. An appendix gives addresses for those "needing support in escaping religion".