"Extraordinary events require extraordinary evidence.&q

[The Tanager]

If anyone is interested, I'd like to look at this, both on what those who use it mean and if it is a reasonable thing to ask of others. Does it mean that things like alien abductions, miracles, etc. need a different kind of evidence offered for them? Or that they just need more of the same kind of evidences? Both? Something else?

I don't want this to become about a specific argument, but examples may need to be looked at to help in clarifying one's thoughts. What do you all think?

[Divine Insight]

I always take "extraordinary evidence" to simply mean "very compelling evidence".

I see no reason why this evidence would need to be any different from any other evidence.

If Carl Sagan had said, "Extraordinary claims require extra-compelling evidence" the saying most likely wouldn't have caught on the way it did. So let's give Carl credit for knowing how to phrase a cliche in a way that gives it a life of its own.

Edited to add:

I should add here also that in truth extraordinary claims don't really require extraordinary evidence. If standard evidence could be shown for them that would indeed suffice.

I think we need to understand the spirit in which Carl was making this statement. It was no doubt an attempt to get a point across somewhat poetically.

I think all he was really saying is that if someone is going to make an extraordinary claim they better be able to back it up with quite a bit of compelling evidence. And that "quite a bit of compelling evidence" was reduced poetically to simply "extraordinary evidence" which basically means the same thing.

[The Tanager]

Sagan's poetic form definitely helped it catch on and I have no problem with it (just in case that was unclear earlier). The way you take it seems to be a rational expectation to me. I do think it sometimes gets used in a vague way meaning something more like "the standard kind of evidence just won't do here, even if I can't tell you what kind of evidence would or why something else should be expected."

[marco]

If anyone is interested, I'd like to look at this, both on what those who use it mean and if it is a reasonable thing to ask of others. Does it mean that things like alien abductions, miracles, etc. need a different kind of evidence offered for them? Or that they just need more of the same kind of evidences? Both? Something else?

I don't want this to become about a specific argument, but examples may need to be looked at to help in clarifying one's thoughts. What do you all think?

I don't think there is any great complexity involved. If a man says he was at place X the previous evening, an account of what happened and the names of people who saw him might suffice. If someone says he saw a corpse walking down the road it would not suffice to be told when it happened and what the corpse was wearing. Even a photograph would not help, since the main suspicion would be the person is lying or was deceived. Exceptional evidence would have to remove these possibilities, rather than just describe the walking corpse.

[The Tanager]

I don't think there is any great complexity involved. If a man says he was at place X the previous evening, an account of what happened and the names of people who saw him might suffice. If someone says he saw a corpse walking down the road it would not suffice to be told when it happened and what the corpse was wearing. Even a photograph would not help, since the main suspicion would be the person is lying or was deceived. Exceptional evidence would have to remove these possibilities, rather than just describe the walking corpse.

But what do you think would count as exceptional evidence?

[marco]

But what do you think would count as exceptional evidence?

I think we recognise the Snark when we see it, and then there is an alarming consequence. We change our position fundamentally or perish.

We are some temporal distance from the alleged event now so if indeed a miracle happened then we would need another miracle, now, to persuade us. If it can happen once, it can happen twice. I see no reason for an obdurate refusal to withhold this evidence if it is asked for since we have been told that we will get a response when we make a request.

"Ask and it will be given to you; seek and you will find; knock and the door will be opened to you." Matthew 7: 7

God of course would avoid an ambiguous answer, unlike the Oracles of old.

[wiploc]

But what do you think would count as exceptional evidence?

If believing a claim would require that you tear down your intellectual scaffolding and build it anew, that is an extraordinary claim. The more scaffolding you have to tear down, the more extraordinary the claim.

Suppose I claim that the word is flat. What would it take for you to be able to believe that? All the globes would have to go. The globe makers would have to be part of a massive conspiracy, right? All those stories of people who go around the world, lies. And on and on and on.

That would be an extraordinary claim, and we would presume it to be false. That doesn't make us 100% sure of its falseness, but we'd be so confident as to be justified in dismissing the claim--in the absence of surprising, shocking, evidence.

If somebody tries to sell you a perpetual motion machine, you will rightfully assume that's he's crazy, deluded, dishonest, or maybe all of the above. You don't have to investigate his claim, because it is extraordinary: It is presumptively false.

Thomas Jefferson wrote something like, "I would sooner believe that two Harvard professors are lying than that rocks fall from the sky." It turns out that rocks do fall from the sky, but his conclusion was reasonable given the information he had to work with.

What is "extraordinary evidence"? It is however much evidence is required to justify believing an extraordinary claim.

The claim that continents move around on the earth was extraordinary, and we're familiar with the amount and quality of evidence required to prove that it really happens.

Evolution, the round earth, genes, germs, relativity, quanta, Heisenberg's uncertainty, these were all extraordinary claims. And they have all been so robustly proven so that we have to accept them as fact. The amount and quality of evidence required to accomplish that varies by case.

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I apologize for taking so long in the other thread. I don't know why I thought I would have fewer distractions at home. But the internet is definitely more reliable here.

[The Tanager]

I think we recognise the Snark when we see it, and then there is an alarming consequence. We change our position fundamentally or perish.

That is just a little too subjective and vague for me. It is not a solid tool to use in analyzing the truth of something.

[The Tanager]

Suppose I claim that the word is flat. What would it take for you to be able to believe that? All the globes would have to go. The globe makers would have to be part of a massive conspiracy, right? All those stories of people who go around the world, lies. And on and on and on.

I think you are thinking about this the wrong way. The shape of the earth is something we can determine through scientific observation. If the earth was flat, we could find that out through scientific observation. That's not extraordinary evidence. Sure, someone may have to tear their scaffolding down, but it could be rationally torn down through scientific observation, not a surprising, shocking, "I'll know it when I see it" never before seen kind evidence.

I agree that different things may involve greater or lesser amounts of the normal kinds of evidence. Some things are more complex than others.

I apologize for taking so long in the other thread. I don't know why I thought I would have fewer distractions at home. But the internet is definitely more reliable here.

No rush from my end. I'd be surprised if you didn't have more important things going on at home than getting a response back to me.

[wiploc]

Suppose I claim that the word is flat. What would it take for you to be able to believe that? All the globes would have to go. The globe makers would have to be part of a massive conspiracy, right? All those stories of people who go around the world, lies. And on and on and on.

I think you are thinking about this the wrong way. The shape of the earth is something we can determine through scientific observation. If the earth was flat, we could find that out through scientific observation. That's not extraordinary evidence. Sure, someone may have to tear their scaffolding down, but it could be rationally torn down through scientific observation, not a surprising, shocking, "I'll know it when I see it" never before seen kind evidence.

New kinds of evidence is not what this is about. It's about the regular kind of evidence, but there needs to be enough of it to be compelling.

Consider continental drift. Somebody looked at a globe and said, "Look how well South America would fit up against Africa. Maybe it used to be there."

It was an interesting theory, but presumptively false. Even a single mountain would be too big to move around like that, let alone a whole continent.

But then somebody undertook to prove the theory false by looking at the rocks on the west coast of Africa and the east coast of South America. But the rocks did match up. He proved himself wrong and became a convert to the belief in continental drift.

More and more people matched up rocks. They started making amazing claims like, "The Appalachian mountains in America and the Atlas mountains in Africa used to be together, a single mountain chain."

None of this involved new kinds of evidence. It was just the same old kind, scientific observations.

Then maybe people studying shock waves in the earth decided that the earth's solid crust floats on a layer of melted rock. Maybe floating continents can move around? No, they would tear up the crust, throwing a bow wave, in order to move like that. And nothing would have the power to push a continent like that. If you tried to push a continent, you would tear and destroy it.

Then magnetic evidence showed that rocks, and the continents they are in, used to lie at different angles.

We learned that the crust is divided into maybe a dozen major tectonic plates. The edges of the plates are where most of the action is.

If the plates move, then the continents can go along for the ride. You don't move a continent by pushing hard in one place. You move it by pushing gently (with a thermal current of liquid rock) against the whole bottom of the plate.

Everything suddenly makes sense. Continents really do move!

Thus, one scientific revolution. An extraordinary claim was eventually supported by so much regular evidence of such a compelling nature that the claim no longer seems extraordinary.

Note: I don't claim to know anything about geology. I confabulated this story not to set the record straight but to illustrate a point about what kind of evidence is needed to change our minds on even the most outlandish of claims.

Regular evidence. Regular evidence is the answer. There just needs to be a lot of it. The extraordinary thing about it is that there's a lot. Or it has to be compelling in some other way.

It fits together. It supports other observations. It allows predictions. It is falsifiable, but when the tests are done, they support it instead of falsifying it. It makes sense of the world.

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Now consider your idea about extraordinary evidence. Suppose a theist says she has an invisible friend who walks on water, turns water into wine, jumps over tall buildings in a single bound, stops the sun, can do anything, can't defeat iron chariots, can't be seen but can be seen, is totally just but arbitrarily tortures people forever, is love but tortures people forever, and so on.

And now suppose that a skeptic says something like, "That's an extraordinary claim, so you need extraordinary evidence to support it. It can't be scientific evidence, based on logic and observation, it has to be some new kind of evidence that nobody's ever seen before. And, in the absence of such evidence, I'm not going to believe your claim."

That just makes the skeptic into an idiot. That's not what any advocate of "extraordinary evidence" means by that term.