In correspondence with a Maarten Boudry, a Belgian philosopher of science, I’ve learned that my contretemps with P.Z. about the nature of empirical evidence for God is actually more than a century old. (As you may recall, I listed some evidence that would convince me of the existence of a god, while P.Z. argued that no evidence, however bizarre, could support the existence of a divine being.)

In my strident and militant New Republic article “Seeing and believing”, I wrote the following:

Many religious beliefs can be scientifically tested, at least in principle. Faith-based healing is particularly suited to these tests. Yet time after time it has failed them. After seeing the objects cast off by visitors to Lourdes, Anatole France is said to have remarked, “All those canes, braces and crutches, and not a single glass eye, wooden leg, or toupee!” If God can cure cancer, why is He impotent before missing eyes and limbs?

I’m now informed that this sentiment was actually expressed not by Anatole France, but by one of his friends.  Moreover, France—playing the role of either P.Z. or Massimo Pigliucci—impugned the probative value of those wooden legs at Lourdes.  Boudry sent me the quotation given below (my translation follows), taken from France’s Le Jardin d’Epicure (1895).  I’m putting the whole thing down for the sake those who want the correct reference.

Étant à Lourdes, au mois d’août, je visitai la grotte où d’innombrables béquilles étaient suspendues, en signe de guérison. Mon compagnon me montra du doigt ces trophées d’infirmerie et murmura à mon oreille :

— Une seule jambe de bois en dirait bien davantage.

C’est une parole de bon sens ; mais philosophiquement la jambe de bois n’aurait pas plus de valeur qu’une béquille. Si un observateur d’un esprit vraiment scientifique était appel constater que la jambe coupée d’un homme s’est reconstituée subitement dans une piscine ou ailleurs, il ne dirait point : « Voilà un miracle ! » Il dirait : « Une observation jusqu’à présent unique tend à faire croire qu’en des circonstances encore indéterminées les tissus d’une jambe humaine ont la propriété de se reconstituer comme les pinces des homards, les pattes des écrevisses et la queue des lézards, mais beaucoup plus rapidement.

My translation (excuse the poor French):

When I was at Lourdes in August, I visited the grotto where innumerable crutches had been put on display as a sign of miraculous healing. My companion pointed out these trophies of illness and whispered in my ear:

“One single wooden leg would have been much more convincing.”

That seems sensible, but, philosophically speaking, the wooden leg has no more value than a crutch. If an observer with true scientific spirit witnessed the regrowing of a man’s severed leg after immersion in a sacred pool or the like, he would not say “Oy vey, it’s a miracle! ” Rather, he would say, “A single observation like this would lead us to believe only that circumstances we don’t fully understand could regrow the leg tissues of a human—just like they regrow the claws of lobsters or the tails of lizards, but much faster.”

Here we see two types of methodological naturalism: a brand that dismisses the possibility of supernatural explanation a priori, and another brand that’s open to it.  This is the basis of my debate with P.Z.  Boudry is publishing on this distinction, and we’ll have more on that soon.