Jason Engwer has been debating Jon Curry over at the STR blog. I myself have a running, email commentary on Curry’s remarks which I may post once the threat runs its course. For now I wish to make a general observation.
Curry’s remarks are very scattershot, but to the extent that it’s possible to rearrange them in something resembling a coherent argument, I think it goes something like this:
i) Miracles are incredible
ii) Incredible because they’re antecedently improbable
iii) Antecedently improbable because God, if there is a God, doesn’t normally perform miracles.
iv) To evaluate the credibility of a reported miracle, you have to weigh that report against the prior probability of the reported event.
v) It’s irrational to believe in a miracle if a miracle is unprecedented.
vi) Since, by definition, miracles are extraordinary, the overwhelming evidence for the ordinary course of nature automatically outweighs any ostensible evidence for a miracle.
What are we to make of this argument, such as it is? Let’s consider a few comparisons.
Some body functions are autonomic, like your heartbeat. Your heartbeat is automatic. You don’t need to consciously do something to make your heartbeat. It beats on its own, whether you’re awake or asleep. And short of stabbing yourself in the chest with a butcher knife, there’s nothing you can do to stop your heart from beating. You can’t will your heart to stop beating.
Needless to say, that’s a good thing. Life would be very precarious if you had to consciously will your heart to beat.
That’s analogous to what theologians call ordinary providence, and some philosophers call the uniformity of nature.
Then there’s eating and breathing. Breathing is semivoluntary. We don’t have to think about breathing to breathe. The body inhales and exhales on its own, without our conscious direction.
However, it’s possible to voluntarily regulate our breathing. We can hold our breath for short periods of time. That’s useful in singing, swimming, and other related activities. So we can make ourselves stop breathing. And if we pass out, we start breathing again.
Eating is different. You have to do something to eat. The intake of food doesn’t happen all by itself.
Let’s take another example. Water normally flows down hill. If allowed to operate unimpeded, that’s what water does. That’s comes naturally to water.
Yet it’s possible to make water flow uphill. If you build a water pump, you can make water flow uphill. That’s analogous to a miracle.
Now, let’s apply Curry’s logic to these examples.
Suppose Curry saw water flowing uphill. He would summarily discount the reliability of his perception. It must be a hallucination or optical illusion.
Suppose you showed him a water pump to explain this unnatural phenomenon.
Although a water pump supplies ostensible evidence for how the water could flow uphill, that has to be counterbalanced against the antecedent improbability of water flowing uphill. Since water normally flows downhill, it’s overwhelmingly improbable that water ever flows uphill. Therefore, it’s incredible to believe any report, or even your own perception, that water flows uphill. For the probability that such a report or observation can never overcome the towering presumption against its occurrence.
Likewise, suppose a man is put on trial for murder. He’s accused of murdering his roommate by stabbing him to death.
Curry is a juror. Curry votes to acquit.
Why? Normally, the only thing that stops a beating heart is a heart attack. It’s statistically improbable that you will ever die from a stab wound to the heart. In the overwhelming number of cases, the heart keeps beating until you die of natural causes–like old age.
Any evidence for murder must be counterbalanced against the prior probability that a heart pumps blood with autonomic regularity. So the evidence of murder can never outweigh the uniformity of nature. Any evidence to the contrary (e.g. reported murders) is infinitesimal in contrast to the crushing evidence for autonomic functions.
Even if we see a butcher knife sticking out of the victim’s chest, with a bloodstained T-shirt, it’s far more likely that our perception was a hallucination.
Or suppose Jon Curry was reading the Dayton Daily News, and saw a report, accompanied by a photograph, of some newfangled invention call the Wright Flyer. Now you tell me: what’s more plausible? The photograph is obviously a hoax. Manned flight is unprecedented! Unnatural! A flagrant violation of the uniformity of nature! Reports of manned flight are simply incredible. Only superstitious Bible-thumpers would be gullible enough to believe stories like this.
So where does that leave Curry’s argument? Is it antecedently improbable that water flows uphill? There’s no uniform answer to that question since it depends on other variables. Left to its own devices, it’s antecedently improbable that water flows uphill.
However, given a water pump, it’s not antecedently improbable that water flows uphill. Indeed, given a water pump, it’s antecedently probable that water will flow uphill.
More to the point, prior probabilities are irrelevant at this juncture. How do you calcuate the probability that a water pump pumps water uphill? Do you start with the prior probability that water flows downhill? Is that a factor in your calculations? No.
Must the explanation of a water pump overcome a presumption to the contrary? Not at all. The water pump removes any presumption to the contrary. That’s a sufficient explanation. There is only a presumption to overcome in the absence of an adequate mechanism.
So Curry’s objection to miracles is ultimately tautologous: absent a miracle, it’s highly unlikely that an unnatural event ever occurs.
But that’s hardly an objection to the occurrence of an unnatural event given a miracle.
You can’t very well say there’s a presumption against miracles because there’s a presumption against unnatural events. For there is only a presumption against unnatural events given the absence of a countervailing factor, like a miracle. The ordinary course of nature does nothing, of itself, to create any presumption against the occurrence of a miracle.