Does an extraordinary claim require extraordinary evidence?

[harvey1]

Once in a while, you get this doozy of a phrase that many people just agree with because it sounds good. However, I disagree with this statement. In fact, I would say that the extraordinary nature of a claim is only loosely related to extraordinary evidence. That is, it's possible that the evidence supporting an extraordinary claim could be extraordinary, but most of the time, the evidence is not so extraordinary.

Rather, evidence usually accumulates until it forces a paradigm shift in understanding, and it is very often the straw that breaks the camel's back that all the "extraordinary" evidence is re-interpreted in light of the new paradigm. Once the new paradigm is accepted, the former neglected evidence is seen in this new light, and the old paradigm is then seen as being very unsatisfactory to say the least.

So, since people like catch phrases, how about "drastically different paradigms in thought require enough evidence that leads to a drastic re-interpretation of all the available evidence"? Does anyone disagree and still maintain that extraordinary claims need extraordinary evidence?

[QED]

I bet you'd guess that I'd disagree! You're right of course in saying that paradigm shifts can occur after the gentle accumulation of unspectacular evidence, but relative to the previous paradigm, the body of evidence taken as a whole would represent an extraordinary shift if presented in one hit.

So given its typical application, I think the expression well serves the need to remind people of their duty to keep an eye on the parsimony. There seems to be an inbuilt human tendency towards jumping to less parsimonious explanations for things. It's as if we were all newspaper editors looking for a sensational scoop. Strange markings in cornfields? It must be aliens!

[harvey1]

...relative to the previous paradigm, the body of evidence taken as a whole would represent an extraordinary shift if presented in one hit. So given its typical application, I think the expression well serves the need to remind people of their duty to keep an eye on the parsimony.

The problem with that endorsement of extraordinary evidence as being "as a whole" equivalent to extraordinary, is that the statement is misleading and actually meaningless. It's misleading because it leads people to believe that one piece of evidence must be "extraordinary," and this perpetuates the image of science as needing a "missing link" (to use this creationist objection to human evolution as a kind of metaphor). It's meaningless because any scientific claim backed by evidence "as a whole" that is taken in one hit must eliminate any other reasonable possibility. So, the phrase shouldn't be used, in my opinion. Nobody should discredit an extraordinary claim if surrounded by a great deal of ordinary evidence. Afterall, this is the kind of evidence that supports most scientific knowledge. Most of what occurs in science isn't the nuclear-bomb-explodes-therefore-Einstein-is-right variety.

[ShieldAxe]

In my opinion this saying is just a poetic way of saying that we should have evidence to back up our claims. Its not meant to be a scientific axiom.

[harvey1]

In my opinion this saying is just a poetic way of saying that we should have evidence to back up our claims. Its not meant to be a scientific axiom.

Yeah, but wouldn't you rather have a hundred solid pieces of evidence that leave no doubt; rather than an extraordinary claim with one piece of extraordinary evidence that still leaves room for doubt? It would seem to me that it is much harder for a theory to be false if it predicts a hundred pieces of ordinary evidence than if it predicted one major extraordinary piece of evidence. It's much easier to construct another extraordinary claim using the same extraordinary piece of evidence.

This phrase is entirely misleading and meaningless, IMHO.

[McCulloch]

Somethings are accepted as true with very flimsy evidence simply because the effort required to get the evidence is not worth the result or that the fact happens to coincide with the expected result.

If you told me that you had Chicken Soup for lunch, I would believe you, on your word simply because that is a ordinary sort of lunch. If you told me that you had magic kola nut salad for lunch that cured your cancer, I would not believe you. I would need greater evidence than your word to accept that as fact.

This is the common-sense meaning I get when someone says to me, "Extraordinary claims require Extraordinary evidence."

[harvey1]

Somethings are accepted as true with very flimsy evidence simply because...

Not scientific claims. Any claim by science must be well-established on the evidence, as well as eliminating any other reasonable alternate hypothesis. It's just misleading to say that only extraordinary claims need to be extremely well-established before they are accepted as a scientific claim. If it is a scientific claim no matter how ordinary, then there better be sufficient reason to believe that claim is true.

If you told me that you had Chicken Soup for lunch, I would believe you, on your word simply because that is a ordinary sort of lunch.

But, if I made that claim as part of a scientific theory being true (or validated), you should not accept it. It's not a scientifically validated claim.

This is the common-sense meaning I get when someone says to me, "Extraordinary claims require Extraordinary evidence."

Commonsense is sometimes useful, but not in this case. Too many people hear that they need extraordinary evidence and then they think that science has not established all the extraordinary claims of science because the evidence looks mundane. This is a major reason why this phrase should stop being used. It has no function in science. The better approach is to say that every scientific claim needs sufficient evidence to support that claim, and sufficiency is dependent on the elimination of other reasonable possibilities that exist. Science must eliminate other reasonable possibilities prior to making a claim, this is much more of an issue than highlighting the extraordinariness of a claim (which I don't think matters much).

[McCulloch]

Harvey,
Of course you are correct. But in practice, even scientists make assumptions. However, if I were to base a scientific theory on any claim, the rules of evidence should be the same regardless of the extrordinaryness of the claim.

[harvey1]

Harvey, Of course you are correct.].

Well, then help me convince the other atheists that they are wrong about God not existing.

Just kidding...

[juliod]

Does anyone disagree and still maintain that extraordinary claims need extraordinary evidence?

You are mistaking the nature of extraordinary claims as contrasted with ordinary claims. Ordinary claims do not require extraordinary evidence.

Let's say the claim is "There is a farmer named Bob." That's an very ordinary claim, and no evidence need be produced for we reasonable people to believe it is true. No doubt there are several farmers named Bob within 100 miles of anywhere in the continental US.

Another ordnary claim might be "There is a farmer named Bod at this address..." This claim might require a little evidence to support it, if you were sufficiently interested. But since it is ordinary, the evidence it needs to support the claim is also very ordinary. A name in a phone book, for example.

If you say "There is a farmer at this address named Bob who committed multiple murders" then you are moving into the realm of "extraordinary". Obviosuly in this case we would need to seek comprehensive evidence before accepting it. The sort of things the police would, in fact, seek.

Again, the standard is higher again if the claim is "Farmer Bob possesses a wide range of psychic and telekinetic powers."

DanZ