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The strange case of Dave

Dave believes dogs are spies from the planet Venus. He views any canine with great suspicion, for he believes they are here from Venus to do reconnaissance work. Dogs, Dave supposes, secretly send their reports back to Venus, where the rest of their fiendishly cunning alien species are meticulously planning their invasion of the earth. Their spaceships will shortly arrive from Venus to enslave the human race and take over the world. Unsurprisingly, Dave’s friends think he has a screw loose and try to convince him that dogs are comparatively benign pets, not cunning alien spies. Here’s a typical example of how their conversations with Dave go:

DAVE: It’s only a matter of weeks now! The spaceships willarrive and then you’ll wish you’d listened to me. We mustact now—let the government know!
MARY: Look, Dave, dogs are pretty obviously not space invaders, they’re just dumb pets. Dogs can’t even speak, for goodness sake, let alone communicate with Venus!
DAVE: They can speak—they just choose to hide their linguistic ability from us. They wait till we leave the roomqbefore they talk to each other.
PETE: But Venus is a dead planet, Dave. It’s horrifically hotqand swathed in clouds of acid. Nothing could live there, certainly not a dog!
DAVE: Dogs don’t live on the surface of Venus, you fool—they live below, in deep underground bunkers.
MARY: But then how do earth-bound dogs communicate with their allies on Venus? I’ve got a dog, and I’ve never found an alien transmitter hidden in his basket.
DAVE: They don’t use technology we can observe. Their transmitters are hidden inside their brains!
MARY: But Pete is a vet, and he’s X-rayed several dog’s heads, and he’s never found anything in there!
PETE: In fact, I once chopped up a dog’s brain in veterinary school—let me assure you, Dave, there was no transmitter in there!
DAVE: You’re assuming their transmitters would be recognizable as such. They are actually made of organic material indistinguishable from brain stuff. That’s why they
don’t show up on X-rays. This is advanced alien technology, remember—of course we cannot detect it!
MARY: But we don’t detect any weird signals being directed
at Venus from the earth.
DAVE: Of course, we don’t—like I said, remember, this is advanced alien technology beyond our limited understanding!
PETE: How do dogs fly spaceships? They don’t even have hands. So they can’t hold things like steering wheels and joysticks.
DAVE: Really, Pete. Think about it. You are assuming that their spacecraft will be designed to be operated by human hands. Obviously they won’t. They’ll be designed to be maneuvered by a dog’s limbs, mouth, tongue, and so on.

You can see how this conversation might continue ad nauseum.Mary and Pete can keep coming up with evidence against Dave’s belief that dogs are Venusian spies. But, given sufficient ingenuity,Dave can always salvage his core theory. He can continually adjust and develop it so that it continues to “fit” the evidence.


Clearly, Dave’s theory about dogs is not well confirmed by the available evidence. The first moral we can extract from this example is that, whatever is required in order for a theory to be well confirmed, rather more is required than achieving mere consistency with that evidence.

As Dave illustrates, any belief, no matter how ludicrous, can be made consistent with the available evidence, given a little patience and ingenuity. Believe that the earth is flat, that the moon is made of cheese, that the World Trade Center was brought down by the US government, or that George W. Bush is really Elvis Presley in disguise? All these theories can be endlessly adjusted and developed so that they remain consistent with the available evidence. Yet they are obviously not well confirmed. The claim that Young Earth Creationism is at least as well confirmed as its scientific rivals relies crucially on what we might call the “fit” model of confirmation. According to the “fit”
model, confirmation is all about “fitting” the evidence. But more is required for genuine confirmation than mere “fit,” which any theory, no matter how absurd, can in principle achieve.



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