Cambridge Union debate – “God is not a delusion”

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Cambridge Union – ‘This house believes that God is not a Delusion’– Opening Speech by Peter S. Williams


According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV 2000, p. 765) a delusion is:


‘A false belief based on incorrect inference about external reality that is firmly sustained despite what almost everyone else believes and despite what constitutes incontrovertible and obvious proof or evidence to the contrary. The belief is not one ordinarily accepted by other members of the person’s culture or subculture (e.g., it is not an article of religious faith)…’[1]


Unfortunately for our opponents, theism is an article of religious faith that is ordinarily accepted by people in our culture but which isn’t necessarily inferred from external reality. Hence it is by definition not a delusion! While we forego this purely definitional victory, it does seem fair to note that since the opposition claim that theism isn’t merely intellectually mistaken, but delusory, they thereby shoulder the burden of offering ‘incontrovertible and obvious proof’ for the non-existence of God. Since we don’t know of any ‘incontrovertable’ disproof of God, rather than attack straw men at this point, we’ll simply argue for theism; for if theism is true, it can’t be a delusion. Permit me to sketch three arguments for God.


1) A Moral Argument


  • If god does not exist, then objective moral values do not exist
  • At least one objective moral value exists
  • Therefore, god exists


It’s important not to confuse this argument with the false claim that we must believe in God in order to know or to do the right thing.


What does it mean to say that moral values are objective? Suppose one person thinks the sun goes around the earth, and another thinks the opposite. In this case, we know the earth goes around the sun. Those who believe otherwise, however sincerely, are wrong. Moreover, coming to know that the earth goes around the sun is a matter of discovering truth, not inventing it. Moral objectivism says that ethics is about discovering moral truths, truths that exist even if we fail to discern them. According to moral objectivism there are genuine moral disagreements; and the observation that people sometimes hold different moral opinions just shows that our moral beliefs can be either correct or incorrect according to the moral facts of the matter.


So, are there any objective moral facts? Those who point to the reality of evil as the basis for an argument against God certainly think so; for nothing can be objectively evil if there are no objective values.


John Cottingham reports that ‘the increasing consensus among philosophers today is that some kind of objectivism of… value is correct . . .’[2] For example, atheist Peter Cave (chair of The Humanist Philosophers’ Group of the British Humanist Association) defends moral objectivism by appealing to his intuitions:


‘whatever sceptical arguments may be brought against our belief that killing the innocent is morally wrong, we are more certain that the killing is morally wrong than that the argument is sound . . . Torturing an innocent child for the sheer fun of it is morally wrong.’[3]


The properly basic moral intuition that torturing innocent children for fun is wrong isn’t undermined by the existence of the psychopath who enjoys torturing children. By the principle of credulity, torturing an innocent child for fun clearly isn’t merely something that stops the child functioning normally (an empirical observation), or merely something we dislike because of our evolutionary history, or merely something our society has decided to discourage. Rather, torturing an innocent child for fun is objectively wrong. So at least one thing is objectively wrong. Therefore, moral subjectivism is false.


Some moral intuitions are specific (e.g. It’s evil to use children to clear mine fields, as was done in the Iran/Iraq war) and some are general (e.g. it’s always right to choose the lesser of two evils). Of course, our intuitions could be mistaken; but this very admission of fallibility presupposes moral objectivism; for if moral subjectivism were true, no moral claims could be mistaken! As atheist Russ Shafer-Landau argues: ‘subjectivism’s… picture of ethics as a wholly conventional enterprise entails a kind of moral infallibility for individuals or societies . . . This sort of infallibility is hard to swallow.’[4]


Finally, if moral objectivism were false it couldn’t be true that we objectively ought to consider arguments against objectivism, or that we ought to consider them fairly: Knowing this, we see the impossibility of justifying subjectivism, for to embrace an argument for subjectivism would be to take the self-contradictory position that: a) there are no objective moral values, but that b) we objectively ought to accept subjectivism!


Therefore, the second premise of the moral argument seems secure. Turning to the first premise, many atheists acknowledge that ‘if god doesn’t exist, then objective moral values don’t exist’. For example, Jean-Paul Sartre wrote that he found it:


‘extremely embarrassing that God does not exist, for there disappears with Him all possibility of finding values in an intelligible heaven. There can no longer be any good a priori, since there is no infinite and perfect consciousness to think it.’[5]


An objective moral value is a transcendent ideal that prescribes and obligates behaviour; but an ideal implies a mind, a prescription requires a prescriber and an obligation is contingent upon a person. As H.P. Owen argues:


‘On the one hand [objective moral] claims transcend every human person… On the other hand… it is contradictory to assert that impersonal claims are entitled to the allegiance of our wills. The only solution to this paradox is to suppose that the order of [objective moral] claims… is in fact rooted in the personality of God.’[6]



2) A Cosmological Argument


The Leibnitzian cosmological argument builds upon the ‘principle of sufficient reason’:


1) Everything that exists has an explanation of its existence, either in the necessity of its own nature or in an external cause.

2) The universe exists.

3) Therefore the universe has an explanation of its existence.

4) If the universe has an explanation of its existence, that explanation is God.

5) Therefore, the explanation of the universe’s existence is God.


Since the universe obviously exists, non-theists must deny premises 1 or 4 to rationally avoid God’s existence.


Many philosophers think that Premise 1 – the principle of sufficient reason – is self-evident: Imagine finding a translucent ball on the forest floor whilst hiking. You‘d naturally wonder how it came to be there. If a fellow hiker said, ‘It just exists inexplicably. Don’t worry about it!’ you’d wouldn’t take him seriously. Suppose we increase the size of the ball so it’s as big the planet. That doesn’t remove the need for explanation. Suppose it were the size of the universe. Same problem.


Premise 4 – ‘If the universe has an explanation of its existence, that explanation is God’ – is synonymous with the standard atheistic claim that if God doesn’t exist, then the universe has no explanation of its existence. The only other alternative to theism is to claim the universe has an explanation in the necessity of its own nature. But this is a very radical step and we can’t think of any contemporary atheist who takes it. After all, it’s coherent to imagine a universe made from a wholly different collection of quarks than the collection that actually exists; but such a universe would be a different universe, so universes clearly don’t exist necessarily.


Suppose I ask you to loan me a certain book, but you say: ‘I don’t have a copy right now, but I’ll ask my friend to lend me his copy and then I’ll lend it to you.’ Suppose your friend says the same thing to you, and so on. Two things are clear. First, if the process of asking to borrow the book goes on ad infinitum, I’ll never get the book. Second, if I get the book, the process that led to me getting it can’t have gone on ad infinitum. Somewhere down the line of requests to borrow the book, someone had the book without having to borrow it. Likewise, argues Richard Purtill, consider any contingent reality:


‘the same two principles apply. If the process of everything getting its existence from something else went on to infinity, then the thing in question would never [have] existence. And if the thing has… existence then the process hasn’t gone on to infinity. There was something that had existence without having to receive it from something else…’[7]


A necessary being explaining all physical reality can’t itself be a physical reality. The only remaining possibilities are an abstract object or an immaterial mind. But abstract objects are causally impotent. Therefore, the explanation of the physical universe is a necessarily existent, transcendent mind.

3) An Ontological Argument


As the ‘greatest possible being’ God is by definition a necessary being. A necessary being is by definition a being that must exist if its existence is possible. Hence we argue:


  • If it is possible that God exists, then God exists
  • It is possible that God exists
  • Therefore, God exists


A ‘great-making property’ is any property that a) endows its bearer with some measure of objective value and which b) admits of a logical maximum. A sock isn’t more valuable than you because it’s smellier than you; and however smelly a sock we imagine, it’s always possible to imagine a smellier one. Smelliness isn’t a great-making property. On the other hand, power is a great-making property, one that has a logical maximum in the quality of being ‘omnipotent’. Likewise, necessary being is the maximal instantiation of a great-making property. Even if Kant was right to argue that saying something ‘exists’ doesn’t add to our knowledge of its properties, to say that something ‘exists necessarily’ certainly does add to our knowledge of its properties. Hence most philosophers agree that if God’s existence is even possible, then, as a necessary being, He must exist.


Unlike ‘the tooth fairy’ God couldn’t just happen not to exist despite His existence being possible. To deny the existence of the tooth fairy, one needn’t claim that its existence is impossible. However, to deny the existence of God one must make the metaphysically stronger claim that His existence is impossible. But the claim that God exists clearly isn’t on a par with the claim that there exists a round square! Many atheists acknowledge that the idea of God is coherent. Indeed, atheist Richard Carrier warns that arguments for thinking otherwise are:


‘not valid, since any definition of god (or his properties) that is illogical can just be revised to be logical. So in effect, Arguments from Incoherence aren’t really arguments for atheism, but for the reform of theology.’[8]


Moreover, humans exhibit non-maximal degrees of great making properties (such as power, knowledge and goodness), and this supports the hypothesis that maximal degrees of great-making properties can co-exist over the hypothesis that they cannot.


Finally, the moral and cosmological arguments, by confirming various aspects of the theistic hypothesis, provide independent grounds for thinking that the crucial second premise of the ontological argument is more plausible than its denial.




In conclusion, to show that belief in God is a delusion, the opposition must both rebut our cumulative case for theism and offer ‘incontrovertible and obvious proof’ of God’s non-existence. Until and unless they accomplish these goals, I recommend the motion to the house.



[1] Stanford Encyclopedia of Philosophy,

[2] John Cottingham, ‘Philosophers are finding fresh meanings in Truth, Goodness and Beauty’, The Times (June 17, 2006).

[3] Peter Cave, Humanism (OneWorld, 2009), p. 146.

[4] Russ Shafer-Landau, Whatever Happened to Good and Evil? (Oxford), p. 16-17.

[5] Jean-Paul Sartre, Existentialism Is a Humanism (Yale University Press, 2007), p. 28,

[6] H.P. Owen, ‘Why morality implies the existence of God’, edited extract from The Moral Argument for Christian Theism (George Allen & Unwin, 1965), in Brian Davies (ed.), Philosophy of Religion: a guide and anthology (Oxford, 2000), p. 648.

[7] Richard Purtill, quoted by Charles Taliaferro, Contemporary Philosophy of Religion (Blackwells, 2001), p. 358-359.

[8] Richard Carrier, Sense & Goodness Without God (Author House, 2005), p. 276.