Question.... (Processes of Logic)

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But that isn't what he is talking about. In fact, what you've done isn't really proving a negative.

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I agree in a more restircted sense.Firstly, it is reasonably clear, I think, that crashfrog has in mind (though not explicitly, so I may be wrong) not just a negative, but more especially a naegative existenial proposition. Although not explicit in the statement you can't prove a negative, it is clarified in crashfrog's examples.Secondly, RhRain did quite elegantly prove a negative existential proposition. But Rh did so in a very special case indeed - a case where all possible observations can be canonically defined without actual definitions. I think Rh is aware of this special case, and correctly indicates this.So is it true that one cannot prove a negative existential proposition? Well, if it were, it would lead us to a delightful paradox ... "There exist no provable negative existential propositions" is itself a negative existenial proposition which, if true would mean ...Well, you see where that is going!Cut the Gordian knot and get back to empiricism!Rh does not prove a negative existential proposition in the second example. I guess you did not intend to, did you?

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In that case, I was showing a specific negative case. ...
In this case, we can list all the possible outcomes: The bacteria mutated or the phage mutated.

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Correct ... sorta. In this example a negative existential proposition would be of the form There exist no bacteria in this sample which have mutated. etc. Given the finite nature of the set, you could probably observe all instances. The interesting cases of negative existential propositions are where the size of the set is unknown and not all ases are observable. Proving in a negative in such a case ... that's the narrower definition, I guess.

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I prefer "WWJDFAKB": "What Would Jesus Do For A Klondike Bar?"

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Before moving to the States, I didn't know there was such a thing as a Klondike Bar. I was deeply puzzled by all these references to Alaskan saloons and Jesus' apparent interest in them. I'm now less puzzled, but also less amused. Some of the answers I heard were much funnier when I thought they referred to hostelries.