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, except she's an incorporeal dragon and the paint
won't stick.'
An so on. I counter every physical test you propose with a
special explanation of why it won't work.
Now, what's the difference between an invisible, incorporeal,
floating dragon who spits heatless fire and no dragon at all? If
there's no way to disprove my contention, no conceivable experiment
that would count against it, what does it mean to say that my
dragon exists? Your inability to invalidate my hypothesis is not at
all the same thing as proving it true. Claims that cannot be tested,
assertions immune to disproof are veridically worthless, whatever
value they may have in inspiring us or in exciting our sense of
wonder. What I'm asking you to do comes down to believing, in
the absence of evidence, on my say-so.-Carl Sagan