Can someone explain the usage of the phrase "Extraordinary claims require extraordinary evidence"?

First I want to say that I am not looking for a debate I just want some clarification. Sometimes when people discuss things like life after death or god some people say "Extraordinary claims require extraordinary evidence". How is this scientific? Is there an objective way to determine if a claim is extraordinary and is there an objective way to determine if a piece of evidence is extraordinary? As far as I know the answer is no. With the information I have at hand I have no choice but to conclude that what counts as an extraordinary claim or evidence is completely subjective and therefore not scientific.

So I must ask is the phrase "Extraordinary claims require extraordinary evidence" a valid scientific argument? Once again I am not looking to debate I just want to know if I am taking the phrase in the right context.

It's something Carl Sagan said to demonstrate the kind of evidence we would need in order to reasonably support certain claims including but not limited to: the existence of God, ghosts, or UFOs. Positive claims such as "ghosts exist" do not seem to fit in at all with what we know about the natural world and thus are considered extraordinary claims. It follows that seemingly highly improbable claims like those would require very strong evidence in order for them to be viewed as highly probable.

Extraordinary claims require extraordinary evidence - RationalWiki

Blueline put it perfectly. Other favourites of mine are David Hume's 'a wise person proportions his belief to the evidence' and a quirky one I've heard from Lawrence Krauss and Tim Minchin: 'don't be so open minded your brain falls out'. I'm not sure who originally said it.

I think the point is, don't just believe things without thinking critically about them first.

If I said I sat on the couch and ate some potato chips, you would probably just take my word for it. If I said aliens abducted me and took me to mars where we had a party, you would probably want strong evidence. You are not going to take my word for it. Even if there was 5 eye witnesses you would probably still wouldn't believe it. The more crazy situation needs more evidence because it is so out there.

I think you are taking the phrase a little too literal. It isn't about having extraordinary evidence, but just having solid evidence for the claim you make. The bigger the claim the more evidence you need. Like in my example, having the empty bag of potato chips would probably be sufficient for the first, however for the second you need evidence to support aliens exist, that people can survive on mars, and that they abducted you.

In the case of the afterlife, if you are making claims that you know exactly what happens when you die, you need proof that there is an afterlife, and that it is the way you described.

It sounds flashy and cool, despite having some truth behind it. It's got bravado.

There is nothing subjective at all about it. For a claim to be "extraordinary", it must have a probability based on our current state of knowledge of below 1%. This can all be formalized with statistical methods. Just because a phrase uses qualitative language like "extraordinary" does not mean it has no quantitative basis and attempting to reject it sounds like it's more motivated by ideologies that can't stand up to scrutiny then a genuine argument for tabooing it.

Edit:
I feel like I should qualify what "current state of knowledge" entails. It's in essence the set of all beliefs held by the subject. Each belief has a percentage bound to it.

So, for example: I am 80% sure that Sally likes me. Now if I encounter a situation where she does not respond to my greeting on the street, that will downgrade my certainty by a certain percentage. However a key factor her is that it is not an on/off switch. Let's say I am 60% sure now that she likes me. Perhaps she was in deep thought or simply did not hear me.

Now let's say that this situation happens over and over again, now my confidence that Sally likes me is 30% or so. However, it can never drop to zero. There is always a chance that new evidence will come in that will bolster the likelihood up to maybe 40% or eventually to 80% again.

An extraordinary claim like telepathy has a likelihood of below 1%. This does not mean it is impossible but it does mean that it is worth proportionally less of your time investigating and that the burden of providing proof should be on the agent that is claiming as opposed to yourself. That is why it is in fact virtuous to refuse to investigate some things that fall below a certain point of likelihood. Your time is precious and you are not obliged to entertain a concept that is absurd from your reference frame.

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Originally Posted by DeviantThinker

For a claim to be "extraordinary", it must have a probability based on our current state of knowledge of below 1%.

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That is a preposterous claim! You could as well have quoted a figure of 10% or 0.1%. There is no objective level for "extraordinary".

However, I very much like the rest of your argument (which is entirely Bayesian :) ).

Generally speaking, the phrase "extraordinary claims require extraordinary evidence" tends to be used ad nauseam by people who like the status quo, and don't want anything changed. It is almost designed to stifle all true research.

Often it is used in situations, where it is completely inappropriate. For example in the controversy:

"ghosts exist" vs. "ghosts do not exist."

Some people would happily say that it requires more evidence to prove the existence of ghosts, than their non-existence. But neither side has any solid evidence on their side at all, so they are pretty much equally far away from winning the argument. (Notice here that the pro-ghost side needs only find one ghost in the whole universe to be correct, whereas the anti-ghost side needs to prove that the entire universe is positively ghost-free. The anti-ghost claim is therefore immensely much bigger than the pro-ghost claim. Their need for evidence is the same though).

The reason many people feel a need for more evidence for one side, than for the other, is often that they start with a great deal of belief in one side and disbelief in the other, and it takes much evidence to shift them away from this position (as DeviantThinker very nicely detailed). Ultimately, however, their starting position is chosen by faith, or "feel". And it holds no objectivity at all, if it is biased.

I should probably add, that some times the claim is made when an extraordinary amount of evidence already exists on one side of the argument, in which case clearly an even bigger amount of evidence is needed to sway the argument.

For example with the issue:

"No person in the world can speak english" vs. "At least one person can."

There has already been collected massive amounts of evidence in favor of people speaking english, so in order to bring the first claim to win the argument, an even more colossal amount of evidence would be needed. (Now, don't ask me how they would go about gathering that evidence :rolllaugh: ).

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That is a preposterous claim! You could as well have quoted a figure of 10% or 0.1%. There is no objective level for "extraordinary".

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I have to admit that in retrospect, that was a bit of a blanket statement.
However, due to the digital nature of how our brains parse beliefs (I believe/I don't believe), I feel that there must be a point somewhere where a belief falls below the threshold that warrants additional effort to investigating it. 1% is admittedly a rather arbitrary percentage though.

There certainly is a danger of suppressing research based on this phrase, particularly when used by those with a poor grasp of probability and an ideological axe to grind.

I have to disagree with some of your later sentiments though. Correct me if I'm wrong but it sounds like you are advocating the idea that absence of evidence is not evidence of absence. I disagree with this often abused notion. Absence of evidence can range from anywhere between very weak to strong evidence of absence. It is contingent on how likely the observation in question would result from a cause.

For example: the absence of evidence for extraterrestrial life qualifies as very weak evidence of absence since we do not possess instrumentation that is powerful enough to test a significant sample of the universe for life. What's more, there is indirect evidence such as clouds of amino acids and water that at the very least make the formation of life outside our planet possible, if not very probable given the wide field of space and time for it to occur.

However, in the case of ghosts, absence of evidence is very strong evidence for absence because we have had ample opportunity to test causes that should result in such an observation. They have all turned up dry. We also have indirect evidence to suggest that purported ghost sightings are likely the result of infrasonic frequencies that occurs due to old fashioned plumbing and other causes. Frequencies around 18Hz (basically the range of tiger growls) can evoke feelings of dread, an evil presence and terror in subjects. 19Hz can cause outright hallucinations.

For a more in depth critique by someone better versed than me:
http://lesswrong.com/lw/ih/absence_o...ce_of_absence/

19hz causes hallucinations? That is a biased bull and a disgusting use of science.

When the eye sees an orange and sends signals to the brain we call it sight. But when that same brain reacts to 19hz, which exists in the environment as much as that orange, you call it hallucination?

Lame.

Science can not define what is or what is not real. Human bias does not. All the science has said is "19hz, that which exists in the environment, creates this experience". Sight, smell, touch, they call create experiences based on whats in the environment. What's the difference? THERE IS NONE. The only difference is what that individual calls reality. And after all, doesn't the science say it doesn't matter who the human is, atheist or theist? Anyone and everyone will experience something when exposed to 19hz. And that is a damn legitimate experience of reality as any other.

But instead of asking questions like "Well why the hell do humans even have this experience when exposed to 19hz" people instead use this science to blanket carpet the "supernatural" experience as nothing more than a mere hallucination. And its absolutely disgusting and insulting to the depth of the human experience, which is so vastly more than what materialists like to pretend it is.

What I saw was seen by five other people, at different times, without prior communication to each other. It reacted intelligently and was not directly accompanied with either dread, evil presence or terror. It's illogical to even insist that this experience is simply a hallucination, as it was seen by five other people, at different times, without prior communication. I can say that all day but the materialist still won't get it.

So how does the materialist respond to my experience? They deny it 100%. They can't accept on any level of their being that my words or true, or the words of 100's of thousands for that matter. They'll continue to bark "hallucination" regardless of how many people experience, the same damn thing (which is the working definition of reality).

Fck the materialist agenda. Extraordinary claims require extraordinary evidence? I sure has hell do not need to provide evidence for what I experience, and neither does anyone else. And this is where the materialist gets it wrong. Its one thing to demand of religions evidence for the dogma they ask us to believe in, its another to completely dismiss the other half of the human experience.

The (scientific) FACT that certain frequencies generate positive or negative emotions regardless of that person's bias for music, speaks profoundly of the human condition and the reality we live in. Even more profound when you understand that everything that is, is, because of frequencies. That is science. That is what real science is all about.

Now, most likely, my eyes will react to the text below me and hallucinate a post.

Ok, it's clear that I have tread on some ideological toes here so I will go through this methodically.

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Originally Posted by juroara

19hz causes hallucinations? That is a biased bull and a disgusting use of science.

When the eye sees an orange and sends signals to the brain we call it sight. But when that same brain reacts to 19hz, which exists in the environment as much as that orange, you call it hallucination?

Lame.

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By your unreasonable demands, there can not be any thing such a hallucination because all mental phenomena are the result of a stimulus, whether internal or external. A figure appearing when there is none qualifies as a hallucination, whether or not it was initially sparked from infrasound.
This was a figure created by your imagination, not a one to one mapping of an ultrasonic perception onto the visual.

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Science can not define what is or what is not real. Human bias does not. All the science has said is "19hz, that which exists in the environment, creates this experience". Sight, smell, touch, they call create experiences based on whats in the environment. What's the difference? THERE IS NONE. The only difference is what that individual calls reality. And after all, doesn't the science say it doesn't matter who the human is, atheist or theist? Anyone and everyone will experience something when exposed to 19hz. And that is a damn legitimate experience of reality as any other.

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I don't really understand what the point here is, if any. If you are claiming that perception equals external reality, then I would invite you to take hallucinogens and jump off a cliff in order to fly. The fact of the matter here is that perception equals anything but external reality. Perception is a virtual representation of the tiny pockets of reality that our extremely limited senses can provide for us. What's more, much of it is completely conjured up by our brain based on prediction algorithms. This is an indisputable fact at this stage of research.

I would also point out that for all your frankly embarrassing vitriol, it you who has misrepresented science here. Yes science does not define what is real or not because definitions do not even come in to the picture. What science does do better than any approach there is to date is to test if something is real or not. Claiming that scientific consensus has no bearing on what is likely or not is a completely scandalous opinion and is little different from saying science is worthless.

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But instead of asking questions like "Well why the hell do humans even have this experience when exposed to 19hz" people instead use this science to blanket carpet the "supernatural" experience as nothing more than a mere hallucination. And its absolutely disgusting and insulting to the depth of the human experience, which is so vastly more than what materialists like to pretend it is.

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Sure, that's totally what scientists do. I mean, it's not like that discovery prompted further enquiries into how stimuli below direct human perception can cause conscious sensations. /s
No, what you are objecting to is not that scientists don't investigate things but rather that their lines of inquiry don't flatter your particular world view. I hate to be the one to tell you but nature does not give two shits how disgusted or insulted her results make you feel. Nature is. Also, kudos on claiming that materialism has any bearing on defining what the "depth of the human experience" is or that it is either your world view or the materialist's (many idealists and dualists would find the notion of ghosts equally absurd).
The only thing in dispute is how closely does that human experience correspond to external reality.

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What I saw was seen by five other people, at different times, without prior communication to each other. It reacted intelligently and was not directly accompanied with either dread, evil presence or terror. It's illogical to even insist that this experience is simply a hallucination, as it was seen by five other people, at different times, without prior communication. I can say that all day but the materialist still won't get it.

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What did you saw, exactly? How closely did your testimony match those of the other five people? How exactly did it react intelligently? I'm entertaining this in mere jest of course since an anecdote sample size of six means little.

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Extraordinary claims require extraordinary evidence? I sure has hell do not need to provide evidence for what I experience, and neither does anyone else.

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Actually you do or at least you do if you want to be taken seriously by anyone. I do appreciate the fact that you are trying to shift the burden onto the other person as if we are obliged to believe your testimony unquestioningly (just like religious dogma, btw).

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The (scientific) FACT that certain frequencies generate positive or negative emotions regardless of that person's bias for music, speaks profoundly of the human condition and the reality we live in. Even more profound when you understand that everything that is, is, because of frequencies. That is science. That is what real science is all about.

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What has this FACT have to do with the validity of ghosts? Everything is because of frequencies? I appreciate your need to flatten out the intricacies of scientific terminology but light frequencies and sound frequencies have little to do with each other. Of course both sound and light frequencies have effects on human emotion but they do not in fact map to each other. There is no universal mapping of colours to tones and none of that has to do with the origins of the universe.

This is not science, this is wallowing in awe and ignorance and trying to take every fact and frame it into a convenient narrative, even at the expense of dealing with the details, small and large. Science deals with details, ALWAYS.

Why? Because with sufficiently little detail, anyone can be right and you only learn things by risking being wrong.