Bayes and Jesus, and the Great Pumpkin Is Coming Back

From: Damien Broderick (d.broderick@english.unimelb.edu.au)
Date: Sat May 11 2002 - 20:38:30 MDT


Oh dear oh dear. Calling Dr Tipler:

http://www.nytimes.com/2002/05/11/arts/11GOD.html?todaysheadlines

May 11, 2002
So God's Really in the Details?
By EMILY EAKIN

Economists use probability theory to make forecasts about consumer
spending. Actuaries use it to calculate insurance premiums. Last month,
Richard Swinburne, a professor of philosophy at Oxford University, put it
to work toward less mundane ends: he invoked it to defend the belief that
Jesus was resurrected from the dead.
        "For someone dead for 36 hours to come to life again is, according to the
laws of nature, extremely improbable," Mr. Swinburne told an audience of
more than 100 philosophers who had convened at Yale University in April for
a conference on ethics and belief. "But if there is a God of the
traditional kind, natural laws only operate because he makes them operate."
        Mr. Swinburne, a commanding figure with snow-white hair and piercing blue
eyes, proceeded to weigh evidence for and against the Resurrection,
assigning values to factors like the probability that there is a God, the
nature of Jesus' behavior during his lifetime and the quality of witness
testimony after his death. Then, while his audience followed along on
printed lecture notes, he plugged his numbers into a dense thicket of
letters and symbols - using a probability formula known as Bayes's theorem
- and did the math. "Given e and k, h is true if and only if c is true," he
said. "The probability of h given e and k is .97"
        In plain English, this means that, by Mr. Swinburne's calculations, the
probability of the Resurrection comes out to be a whopping 97 percent.
        While his highly technical lectures may not net Christianity many fresh
converts, Mr. Swinburne's efforts to bring inductive logic to bear on
questions of faith have earned him a considerable reputation in the small
but vibrant world of Christian academic philosophy. Thanks to the efforts
of Mr. Swinburne and a handful of other nimble scholarly minds - including
Alvin Plantinga at the University of Notre Dame and Nicholas Wolterstorff
at Yale - religious belief no longer languishes in a state of philosophical
disrepute. Deploying a range of sophisticated logical arguments developed
over the last 25 years, Christian philosophers have revived faith as a
subject of rigorous academic debate, steadily chipping away at the
assumption - all but axiomatic in philosophy since the Enlightenment - that
belief in God is logically indefensible.
        "They are the first group within 20th-century Anglo-American philosophy to
tackle questions of religious faith using the tools of philosophy," said
Brian Leiter, a professor of law and philosophy at the University of Texas
at Austin and editor of the Philosophical Gourmet Report, which ranks
academic philosophy departments. "It would be accurate to say that it's a
growth movement."
        Mr. Wolterstorff, who retired from Yale in December and in whose honor the
conference was organized, agreed. "And it's not just graybeards," he added,
referring to the dozens of younger scholars and graduate students in
attendance. "Within the general discipline, this development of the
philosophy of religion has been extraordinary."
        To be sure, not all of the movement's philosophers agree with one another,
use the same tactics or even hold the same religious beliefs. Some,
including Mr. Swinburne, for example, are what's known as evidentialists:
they accept the Enlightenment doctrine that a belief is justified only when
evidence can be found for it outside the believer's own mind. According to
the classic evidentialist argument, for faith to be considered rational it
has to be supported by independent proof, and there simply isn't any.
(Asked what he would say if God appeared to him after his death and
demanded to know why he had failed to believe, the British philosopher and
staunch evidentialist Bertrand Russell replied that he would say, "Not
enough evidence, God! Not enough evidence.")
        In "The Existence of God" (Oxford University Press, 1979), Mr. Swinburne,
a Greek Orthodox Christian, tried to meet the evidentialist challenge using
Bayes's theorem. Supplying pages of intricate, technical argumentation to
back up his claims, he wrote that many natural phenomena - including the
universe itself - are, well, if not incontrovertible proof of God's
handiwork, at least "more probable if there is a God than if there is not."
(Mr. Swinburne, it turns out, is not the first to enlist Bayes's theorem in
defense of religion. In a 1763 paper presented to the British Royal
Society, the minister Richard Price used it to show there was good evidence
in favor of the miracles described in the New Testament.)
        More influential at the moment, however, are the "reformed
epistemologists" led by Mr. Plantinga and Mr. Wolterstorff, who are
Calvinists. These scholars reject the evidentialist insistence on
independent proofs. After all, they point out, the ability to distinguish
good evidence from bad requires reason, but why trust our ability to
reason? Where's the proof that our reason is any good? For the
evidentialists, reason is considered a "basic belief," one that doesn't
require additional evidence to be true. But if reason can be considered a
basic belief, then so, too, say the reformed epistemologists, can faith in
God.
        Accepting faith as a basic belief, they say, does not make faith
irrational. On the contrary, they insist, a belief can lack independent
evidence and still be rational. Some beliefs are simply self-evident. Most
people know that 1 + 1 = 2, Mr. Wolterstorff points out, just as they
accept beliefs about their bodily state - like "I feel dizzy" - without
having to consult other sources. "We believe lots of things that don't have
publicly formulated arguments," Mr. Wolterstorff said. "Reformed
epistemology challenges the need for arguments."
        To buttress their case, the reformed epistemologists lean on Thomas Reid,
an 18th-century Scottish "common sense" philosopher, who, arguing that many
legitimate beliefs are simply instinctual, complained: "Are we to admit
nothing but can be proved by reason?"
        But despite their intricate arguments, some critics - including Christians
- worry that reformed epistemologists make it far too easy to justify any
belief, no matter how absurd. Mr. Plantinga calls this the Great Pumpkin
Objection. As he stated the problem in a seminal 1983 essay, "Reason and
Belief in God": "If belief in God is properly basic, why cannot just any
belief be properly basic? What about voodoo or astrology? What about the
belief that the Great Pumpkin returns every Halloween? Could I properly
take that as basic?"
        The answer, as you'd expect, is "certainly not." But explaining why turns
out to be a formidable challenge. Mr. Plantinga has devoted three thick
volumes and the last 20 years to the effort, stressing, among other things,
that for a belief to be justified, it must be held by a person whose mental
faculties are functioning properly.
        More aggressively, he has suggested that our capacity for true beliefs is
proof that a divine creator - rather than Darwinian natural selection - is
behind evolution: if human beings evolved by random process from mentally
primitive creatures, how could we be sure that any of our beliefs -
including our belief in evolution - are true?
        At the Yale conference, however, neither Darwin nor the Great Pumpkin
Objection seemed any more pressing than conundrums that have dogged
Christianity far longer - occasionally giving the event the aura of a
medieval synod. If God is omnipotent and wholly good, why does he permit
evil to occur? the philosophers wondered. And if God ultimately decides
what happens in the world, in what sense can human beings be said to have
free will?
        Mr. Swinburne also came in for his share of questions. "Bayes's theorem
provides a model of learning from experience," one philosopher observed.
"As time goes by, it seems you would accumulate more evidence against the
Resurrection because the expected Second Coming doesn't occur."
        Mr. Swinburne acknowledged the point was worth considering. But he wasn't
about to concede it entirely. When Jesus spoke about the Second Coming, "he
might have said soon but he certainly didn't say when," Mr. Swinburne
insisted, adding, "I don't think you have a very strong case there."



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