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Editorial Review Product Description
Does God exist?
This is probably the most debated question in the history of mankind. Scholars, scientists, and philosophers have spent their lifetimes trying to prove or disprove the existence of God, only to have their theories crucified by other scholars, scientists, and philosophers. Where the debate breaks down is in the ambiguities and colloquialisms of language. But, by using a universal, unambiguous language—namely, mathematics—can this question finally be answered definitively? That’s what Dr. Stephen Unwin attempts to do in this riveting, accessible, and witty book, The Probability of God.
At its core, this groundbreaking book reveals how a math equation developed more than 200 years ago by noted European philosopher Thomas Bayes can be used to calculate the probability that God exists. The equation itself is much more complicated than a simple coin toss (heads, He’s up there running the show; tails, He’s not). Yet Dr. Unwin writes with a clarity that makes his mathematical proof easy for even the nonmathematician to understand and a verve that makes his book a delight to read. Leading you carefully through each step in his argument, he demonstrates in the end that God does indeed exist.
Whether you’re a devout believer and agree with Dr. Unwin’s proof or are unsure about all things divine, you will find this provocative book enlightening and engaging. ... Read more Customer Reviews (42) 
Good intro to Bayesian concepts, including limitations
As a mathematician, I found the "derivation" of Bayes' equation in Chapter 4 a good explanation for a determined non-math person.In fact, I think Chapter 4 is the best part of the book.I continued on to see how Unwin would come up with his probabilities.First, as the main prior probability, he declares a 50/50 chance that god exists, because he thinks 50/50 professes maximum ignorance as to whether god exists.That starting point is important to his ultimate conclusion, but it's nothing more than an arbitrary assignment.He then chooses six evidentiary areas to form conditional probabilities which are then plugged in to the Bayes formula to refine the probability of god's existence.His six areas are claimed to be additional evidence to be considered in the problem.
Well, they are not evidence - they are philosophical discussions, and his six probability assignments are based entirely on what he believes.For example, in E1, he says "I find none of the atheistic explanations of compassion and morality highly convincing."Based on this "finding", he assigns a numerical probability, a "reasonable numerical assignment reflecting the weakness of atheistic explanations."The arguments are weak to him so he picks a low number.Very reasonable.
In his appendix, Unwin explicitly removes all validity to the book's conclusion of 67%.He says:"As I identified my evidentiary areas for Prop. G, made my assumptions, and selected my numbers, I had no doubt that you, the reader, might have taken a different path.Your assigned numbers might have been different. ... One must expect the potential for divergence of opinion in any analysis." Well said, except this book is not an analysis - it's ultimately a rhetorical argument, thinly dressed in pseudo-math garb.
Less than meets the eye.
Before getting to the meat of this book, two short observations. First, it's heavily padded with text that doesn't need to be there, and the math is explained at such a snail-like pace that it's actually harder to understand and use than necessary. As part of the padding he includes some distracting dialogs that should have been omitted. Also there is a much more compact way to explain the math.
Unwin is a theist. He finally says that he believes in God's existence with 95% confidence. Of that, the Bayesian analysis supplies 67% and "faith" fills in the rest that he needs to be there. This honestly admitted bias heavily influences his estimates of the various factors (that he calls "evidentiary areas") that go into the final 67%. He says he has honestly estimated those factors, but it seems obvious that he selected them so the final result would be in God's favor (since he was a theist long before doing this analysis), but not so overwhelmingly so that his bias would be blatantly obvious. The six factors he includes and their values (even the number six is highly arbitrary) are:
1. The recognition of goodness in the world (d1=10.0)
2. The existence of natural (not human-caused) evil (d2=0.1)
3. The existence of moral (human-caused) evil (d3=0.5)
4. Intra-natural miracles (ones that don't seem to violate known laws) (d4=2.0)
5. Extra-natural miracles (ones that do violate laws of nature) (d5=1.0)
6. Religious experiences. (d6=2.0)
I have swapped d2 and d3 relative to his numbering. He assigns a ratio, d1, d2, ... ,d6 to each factor. Each value is the probability that God exists based on that factor.For example, for factor d1, the existence of goodness, he assigns the value d1=10, meaning that on this factor alone, God is 10 times more likely to exist than not. The other values are similarly assigned. He calls the values 10 and 0.1 "much more (or much less) likely," the value 2 and 0.5 "moderately more (or less) likely, and the value 1 as fully neutral. I agree with these descriptions of the values.
Now for a bit of math, some of which he should have included for simplicity, but didn't. Call D=d1*d2*d3*d4*d5*d6. The Bayesian formula then is
Pa = D*Pb/(D*Pb +1 - Pb),
where Pb is the initial probability of the proposition we are evaluating (the existence of God) , before the factors have been taken into account, and Pa is the final probability of the proposition after we have put in all the factors. Unwin computes five intermediate values for Pb, but this just drags things out and hides the fact that the order in which the values are used does not matter.
Multiplying all the d's, we get D=2. Now he says that the most justifiable value for the initial probability of God is Pb=1/2, on the grounds that it favors neither the existence or nonexistence of God, so is neutral, that is, a "minimum knowledge" value. Given his values of D=2 and Pb=1/2, we get Pa=2/3=67%, the same value that he gets in a much more long-winded way. One concludes that the probability of God is 2/3, that is, God is twice as likely than no God.
Now let's look at his values for the factors. Note that d1 and d2 can be omitted together since their product is just 1. On first examination, that's reasonable, or at least more reasonable than his remaining values.
For d3, the existence of moral evil is inconsistent with God's purported omniscience, omnipotence, and omnibenevolence, at least on the surface. This inconsistency has been discussed by philosophers for centuries, with no final conclusion. Theologians have created excuses for the co-existence of God and evil, such as our free will being more important than avoiding suffering, and that recognition of good is impossible without evil to compare it to. I find that these and the other excuses are farfetched and highly unlikely. Hence I would assign d3 a much lower value, perhaps 0.1.
For d4 and d5, concerning miracles, I observe that there is no objective evidence that any miracle, supernatural or not, has ever occurred. I would therefore simply set d4=d5=1, which has the same effect as leaving them out.
The most questionable value of his is d6=2.0, based on private, personal religious experiences.Such experiences can be induced by music, drugs, and other things, and they have no bearing on the objective existence of God, so I would use d6=1.0. He admittedly uses the Bayesian approach to give justification to personal belief or lack of it, but he says that the (implying objective) probability of God is 2/3.
My values are d1=10, d2=0.1, d3=0.1, d4=1.0, d5=1.0, d6=1.0. I also object to setting the a priori (initial) probability of God to ½, on the grounds that it is an extraordinary claim and the required extraordinary evidence is absent. I will use a value of Pb=0.1. Putting all the value in, I get D=0.1 and Pa=0.011. So in my estimation the probability that God exists, based only on Unwin's six factors, is 1%.
There is a still more serious problem. Unwin's six factors concern the effects of God, not his properties. Many unlikely properties are usually cited, all of which are impossible to prove. I have compiled a list of the standard properties of God and came up with 22, about evenly divided between the general God and the specifically Christian one. These include omniscience, omnipotence, omnibenevolence, eternal existence, infinite presence, and many more. If Unwin's analysis were done using God's properties rather than his effects, the final probability that God exists would be tiny. If I were a believer, faith would have to comprise about 99.999% of my "reasons" for belief. Having read some of Craig, Plantinga, and Swinburne, I suspect that faith is a much larger component of their belief than they would like to admit, and their philosophical justifications are superfluous.
As I said above, Unwin gets 67% for the strictly Bayes-derived probability, and adds in a faith term of 28% to get to his final confidence of 95%. But he obviously started with the 95% figure and used Bayes only to get the mathematical contribution up to a value where faith comprises a minor part and his belief therefore has a rational basis.
His method is interesting and perhaps new in this context, but his values are highly biased in order to get the desired answer. I credit Unwin for first introducing (so far as I know) Bayesian thinking to the God question. Given the totally arbitrary values that he or any other person starts with, I do not place much importance on this method.
Yeahist mathematician refutes many arguments for existence of God
This small book packs a lot in it. It has about 18 different arguments that have been proposed for the existence of God, including most of the usual ones: Prime Mover, Intelligent Design, Anselm's and Gödel's (also a mathematician!) ontological argument, Pascal's Wager, and coincidences such as 91 x 11 x 767 = 767,767. I have read the ontological argument which says that God is that which has all positive properties; existence is a positive property, so God exists. I have noted that you can use this argument also to prove that your most ideal mate or job possible also exists, but this is the first time I have heard this refutation in a book. Paulos uses the example of the most ideal island. He refers to mathematics but he never gets that heavy with mathematical notation, and some of the arguments he reviews are not mathematical, so it really is a refutation by a mathematician of various arguments of God. After refuting all this, does he say anything about his own belief? Yeah, he does. Simple acceptance of what is. I think this is the basic core of some religions such as Friends and Unitarian Universalism. He calls his belief Yeah-ism. Yeah. This book is highly recommended.
Abuses of probability and Bayes' theorem
Abuses of probability and Bayes' theorem
Probabilistic reasonings are abused quite often and sometimes are intentionally deceiving. This is very common in advertising and in politics. However, there is one flagrant abuse of Bayes' theorem which the reader of this book should be aware of, since it takes on a "scientific" posture. I am referring to Stephen Unwin's (2003) bookentitled: "The Probability of God", subtitled: "A simple Calculation That Proves the Ultimate Truth".
First, recall that probabilities are assigned to events, or to outcomes of an experiment, not to objects. There is no such thing as "Probability of a Table", nor of "Probability of the Moon" nor of "Probability of Kukuriku". Therefore, the title of Unwin's book is meaningless. On the book's first page, Unwin wtites: "I use the term probability in its strict mathematical sense and not in the fuzzy, ambiguous way it can be used in common language". That claim is an outright deception. All the book deals exclusively with "the fuzzy, ambiguous" meaning of probability A mathematical probability is assigned to events or to outcomes that can occur. The proposition "G" as defined by Unwin: "God exists", is neither an event nor an outcome of an experiment.
On page 15, Unwin is careful to note that the proposition "I did not have sexual relations with that woman" cannot be judged as true or false unless one defines what is meant by "sexual relations". That is correct. However, there is an abounding discussion of the probability of the proposition "God exists" in the entire book without ever defining who or what "God" is. This renders the entire contents of the book meaningless.
On page 58, Unwin writes: "Here, I think that the expression of complete ignorance (of the truth of proposition "G") is a good case of the 50-50 argument". It is not! He continues: "This is a perfect, unbiased expression of agnosticism". It is not! Clearly, Unwin draws from the symmetry argument applied to the two outcomes of throwing a coin. In the case of proposition "G", it is not clear what the experiment is, nor what the outcomes are.Therefore, the attachment of 50% probability to proposition "G" is totally arbitrary.
The rest of the book is a ridiculous exercise in using "evidentiary areas", in connection with Bayes' theorem to reassess the probability of proposition "G".
It should be noted that, Bayes' theorem allows one to modify probabilities of an event when given additional information. It is not a method of calculating probabilities! Using the same language,and the same kind or reasoning, one can prove anything one wants, and get any probability one wants. Specifically one can "prove" the important propositionthat the probability of "the existence of Kukuriku" is 95%.
Richard Dawkins (2006) commented on Unwin's "proof": "It sounds like a joke" and says that the GIGO principle (Garbage In, Garbage Out) is applicable to Unwin's "proof".
I fully agree with Dawkins that this book is nothing but GIGO. I do not agree, however, that it is a joke, not even a bad joke. It is sheer nonsense, disguised in a scientific language.
Finally, the subtitle of the book is also meaningless, unless one defines what the "Ultimate Truth" is. Once we know what the "Ultimate truth" is, we shall not need to prove it!
A little painful at times...
Well, first off - let me say I'm an atheist...
... Ok - now that most of the religious folks have stopped reading (to protect their fragile sensibilities), I can speak freely...
I cannot say this is a bad book.I do like the writing style, and I found it a very quick read, with few impediments.But while the rudimentary framework laid out by Unwin is simplistic and logical, I can't say the same for his analysis.
The fact of the matter is that Unwin has the foregone conclusion that his conception of god exists.And while he may, at times, allude to the possibility that god does not exist, in almost every aspect of this book, he betrays any objectivity.(for example - in the last paragraph of the book, Unwin's dialog takes it for granted that an after-life exists).
Although Unwin certainly does not surreptitiously pervade his subjectivity, it definitely is present throughout the book.And this is why I felt the book is quite painful at times.There are just so many instances where I don't agree with his logic, or where it is obvious that he is overlooking some fact.So to forgive him for this, for the few instances where he does point out his subjectivity, would be too kind.
So with this in mind, I really only see this book serving as a tool for the faithful to reaffirm their beliefs under the guise of some logical framework.In mercilessly pushing his agenda, I find this book to be a bit of a waste of time for atheist readers - the more adept, of which, will not find anything new in the book, other than a very lengthy dissertation of a theorem of aggregate probabilities that could easily be summed up in a couple of paragraphs.
As for Unwin's analysis... I was disappointed to find that it falls flat onto what amounts to vague feelings about abstract concepts... and really seems to have no objective basis, other than his pre-existing faith.
I wonder, had Unwin been raised by some neolithic religious society, would he have found a rational basis upon which to accept human sacrifice?
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