Re: How are you sure that a given species is truly extinct?

Bob Casanova wrote:
On Sun, 30 Aug 2009 19:02:12 -0700, the following appeared
in talk.origins, posted by John Harshman
<jharshman.diespamdie@xxxxxxxxxxx>:

Bob Casanova wrote:

<snip>

One can easily prove a specific negative, such as "There is
no elephant in my living room"; it's the general negatives
that are more problematic ("No X exists anywhere on Earth"),
and those are the ones I was referring to. When "on Earth"
becomes "anywhere in the universe" such proof becomes
impossible.

I think we can be fairly sure that if there are no ivory-billed woodpeckers on earth, there are also none in the rest of the universe. And it's even a bit easier than that. We don't even have to search Africa, Asia, South America, Australia...

Yes, John, I'm aware of that, and I wasn't referring to
I-BWs. Was my statement incorrect as a general observation
regarding the disproof of negatives?

One could certainly make it correct. (Presumably you didn't intend the double negative.) You can prove a negative by exhaustive search of whatever part of the universe is relevant. Practically speaking, the size of the relevant universe and your ability to exhaustively search it vary immensely with species.

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