Carl Sagan and Proving a Negative


I’m in Canada today for Thanksgiving (the Canadian version), so I don’t have a lot of time to do my usual vomit of atheist thoughts. So instead, I wanted to link something that Jerry Coyne brought up a few days ago on his awesome blog, Carl Sagan’s Parable of The Dragon In My Garage. 

People who grew up with Sagan love the man, his wonder at the natural world around him, and his love for science, speaks to a lot of people whether they are atheist or not. He has a book that is often recommended to ex-theists, The Demon Haunted World (my reading plate gets full), and I still haven’t had a chance to give it a read. 

In that book he brings up the story of a man who says he has a dragon in his garage, but every time the skeptic asks for proof of this dragon, it turns out the dragon has some nature to it that makes it impossible to detect. 

“A fire-breathing dragon lives in my garage”

Suppose (I’m following a group therapy approach by the psychologist Richard Franklin) I seriously make such an assertion to you.  Surely you’d want to check it out, see for yourself.  There have been innumerable stories of dragons over the centuries, but no real evidence. What an opportunity!

“Show me,” you say.  I lead you to my garage.  You look inside and see a ladder, empty paint cans, an old tricycle — but no dragon.

“Where’s the dragon?” you ask.

“Oh, she’s right here,” I reply, waving vaguely.  “I neglected to mention that she’s an invisible dragon.”

You propose spreading flour on the floor of the garage to capture the dragon’s footprints.

“Good idea,” I say, “but this dragon floats in the air.”

Then you’ll use an infrared sensor to detect the invisible fire.

“Good idea, but the invisible fire is also heatless.”

You’ll spray-paint the dragon and make her visible.

“Good idea, but she’s an incorporeal dragon and the paint won’t stick.”  And so on.  I counter every physical test you propose with a special explanation of why it won’t work.

The rest of the story is available here, and was also linked on Coyne’s blog. The story is important, I think, because it speaks to a truth that we often forget to realize. Sure, if you are just talking about the general idea of an entity that we don’t know about, it is hard to say that it doesn’t exist, but when we are talking about a creature that should leave great heaps of evidence in its wake, it takes a lot of work (and back-pedaling) to justify saying that it exists without any proof of it.

This is why we have things like Russel’s Teapot, and the Flying Spaghetti monster, these are entities that show the ridiculousness of the ‘you can’t prove it doesn’t exist’ stance. My personal favorite is the Galactic Space Fish, which is so large that we can’t detect it, but it swims through space. Sure it could exist, but why posit for its existence? There are two easy answers, you were already told that Galactic Space Fishes exist, or you really want Galactic Space Fishes exist.

All we can do is leave out some Galactic bait and see what happens, but in the meantime, I think it is safe to say that fishy smell is coming from somewhere else.  


5 thoughts on “Carl Sagan and Proving a Negative

  1. What if the dragon completely transcends not only the garage, but the house, the town, the city, the state, the country, the planet, the galaxy, and the universe? What if the dragon was said to be responsible for the entire physical world? What if the dragon was said to be the anchor for all morality?

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