"'Pigs can't fly' is falsifiable."
"Oh, is it? Can you prove that no pig is able to fly? I don't think so. You'd need to thorougly test every pig in the world."
OK, let me correct myself here. I posted too hastily this time. Of course "pigs can't fly" is falsifiable in principle. All you need to do is show a pig flying. But someone took me to task earlier in this thread for giving an example of how ID is falsifiable -- because it couldn't actually be done (just as you can't actually make a pig fly).
A more interesting question is whether the theory that "pigs CAN fly" is falsifiable. How could it be falsified? As I suggested in my last post, you'd need to test every single pig in the world and prove that not one of them can fly. And how could you even prove that one particular pig can't fly? How would know that they are just refusing to cooperate with you? I'm talking about absolute, 100% proof here. You may be able to get to 99.9999999999% certainty, but I don't think you can get to exactly 100% certain proof. So then the theory that "pigs can fly" is unfalsifiable, so it is not a valid theory. Oh, but it *is* a valid theory -- just not a very useful one.