According to amazon.com, it was 2003 Feb 20 when the venerable Christian philosopher Richard Swinburne published his book, The Resurrection of God Incarnate (hereafter simply Resurrection). Swinburne, 74 years old as of today (2009 Sep 06), holds an Emeritus professorship at Oxford University, and has spent his academic career arguing for the existence of the Christian God, among other philosophical pursuits. I borrowed Resurrection from my own university library over the summer (of 2009), and acquainted myself with Swinburne's formalized thesis therein.
In the book, Swinburne suggests to the reader four particular probability values. If we accept his choices, then we can plug them into a statistical equation called Bayes' theorem to show that the probability Jesus was God incarnate is about 97%.
This is quite a claim. If we accept probability theory--and most of us do accept it, for good reason--then we are invited to take the single question of Jesus' divinity, and parse it out into four separate issues which can be tied together by Bayes' theorem.
So, what exactly are the four ingredients in this mathematical recipe? First, Swinburne suggests that the probability that God exists, given the evidence from natural theology, is about 50% (p211). Second, he gives possible reasons for thinking that the probability of God choosing to become incarnate, should He actually exist, also approaches 50%. Thirdly, he contends that out of all the religious figures in history, only Jesus Christ is accompanied by a certain threshold of evidence indicating that he might be an incarnation of God; if God really did become incarnate, then Swinburne argues that the probability of exactly one human being satisfying this requirement is a "fairly low" 10% (p212). Fourth, and finally, he tells us that, assuming that God either did not become incarnate or does not exist at all, the probability that some prophet in history would satisfy the evidentiary requirements of the strength which Jesus allegedly satisfied is a distant 0.1% (p213).
Swinburne proceeds to take these four probability values and plug them into Bayes' theorem, ultimately producing a probability value of 97% that Jesus was God incarnate (p214). So goes his unifying argument.
As a fourth-year math major, myself, I can verify that Swinburne's use of Bayes' theorem is, strictly speaking, logically valid. If we accept Swinburne's four suggested probability values, along with a few relatively uncontroversial historical conclusions, then they do indeed show that there is a 97% probability Jesus was God incarnate. So, the spotlight shifts to the four values themselves. Are they accurate?
In selecting an appropriate probability that God exists given the evidence from "natural theology," Swinburne settled on the figure of 50%. Natural theology, for those who may not know, involves philosophical evidence such as the cosmological and teleological arguments for the existence of God. Apparently, Swinburne believes these are convincing enough to bring the otherwise distant probability of God's existence to that of a fair coin toss.
I find this somewhat strange. I get the impression that he believes the actual probability of God's existence given natural theology nears 100%, but he has reduced this value to 50% in order to avoid criticism from those who might not agree with his assessment. Yet why should anyone compromise on the results of these arguments? If at least one of them is acceptable, then the probability that God exists surely exceeds 50%. Conversely, if they are all dubious, then they have little or no significance to the question of God's existence or nonexistence. Which arguments for the existence of God does he suppose have sliding scales of success, whereby they can function just well enough to raise the probability of the existence of God to his preferred assignment?
I for one reject those natural theological arguments, of which I have encountered many. For example, I remain thoroughly unconvinced that God can be defined into existence, as the ontological argument attempts to do. Nor do I believe for a second that we can use our everyday intuition to accurately guess truths regarding causality and the big bang, as the cosmological argument often requires. For me, the probability that God exists after we consider natural theology is exactly the same as whatever it was before we did so.
In the second chapter of Resurrection, Swinburne relates an apparently novel argument, the conception of which may have served as the inspiration for the overall approach. Under the assumption that God exists, he claims a number of reasons, for example supplying atonement for moral infractions, which in good Christian form Swinburne calls "sin" (p38), that God has for choosing to take on human form. This he calls a "Chalcedonian" incarnation (p51), after the Council of Chalcedon by the Roman Catholic Church in AD 451. In his own words: "...his [God's] incarnation could not involve his ceasing to be divine. It must, rather, involve God taking on additionally a human body and a human nature understood as a human way of thinking and acting" (p51).
Swinburne clearly has orthodox Christian doctrine in mind when discussing the possibility that some God might choose to become incarnate in a human vessel. So, if you have problems with evangelical theology, then you may not find Swinburne's argument regarding the Chalcedonian incarnation all that convincing. Even for people like me, who acknowledge the coherency of such theology, we need some good reasons to suppose that God, if he exists, actually agrees. Otherwise Swinburne's claim that there is a 50% chance God would choose to take human form will ring hollow.
We may also ask, as Swinburne did, what is the probability that, if God did become incarnate, we should discover some particular strength of historical evidence to that effect? Swinburne apparently wished to err on the side of caution, choosing an artificially (in his opinion) low value. But is it really so low? Does a reasonable spectrum of probabilities extend below his 10% suggestion? In my opinion, a value close to 1% seems just as valid. Perhaps we could go even lower.
I regard the fourth probability value as the most wildly speculative of them all. Here we are to assess the probability that some unnamed prophet might satisfy the relevant evidentiary requirements of Jesus, despite the assumption that God chose not to take human form. How can we possibly hope to achieve accuracy with such an unintuitive question? Swinburne argues that it would be "immensely unlikely" to think God would "permit" a historical figure to uniquely satisfy evidentiary requirements similar to Jesus (p213), but of course I disagree. Moreover, since I deem the probability that God does not exist as rather high, I would be most concerned with that scenario. What, then, is an appropriate value, if not 0.1%? From my perspective, 10% seems incredibly more reasonable, although of course any value assigned to such an obscure variable will be necessarily dubious.
Suppose, now, that we alter some of the values in Swinburne's equation. Namely, let's say we agree that arguments from natural theology are consistently unsound. So, where Swinburne chose 50%, we might instead assign the probability of God's existence given natural theology a value of only 1%. In that case, the probability that Jesus was God incarnate drops from the 97% value Swinburne gave to a somewhat low 33%.
Suppose further that we reject Swinburne's 0.1% probability that a threshold of evidence exemplified by Jesus mistakenly points to the Chalcedonian divinity of some prophet in history (even Jesus himself), in favor of a more generous 10% value. Then the probability of Jesus being God incarnate drops from 33% to a dramatically lower 0.5%.
If we wished, we could adjust each of the remaining two input values similarly, to push the final probability value lower still. However, I will leave that exercise to my readers, if they are sufficiently interested to track down a copy of Resurrection and learn the formal framework of its central argument.
The aim of Swinburne's book is to use historical evidence and philosophical analysis to make a case that Jesus Christ really was God incarnate. The idea behind this approach is that one does not require religious faith to accept Christianity. Instead we deal only with historical evidence in the natural world, analyzed in light of general philosophical concepts. Similar approaches have quite popular in modern apologetic circles. Apologists Gary Habermas, William Lane Craig and Lydia McGrew, for example, all make arguments from historical evidence that Jesus' body was reanimated after death. Just like Swinburne, they wish to address religious questions with primarily secular tools.
While I laud their efforts, I invariably find them insufficient. Resurrection constitutes yet another albeit inventive attempt in an ostensibly doomed cause.