Help Sagan Stop Doing Kazillions of Backflips in His Grave

I am constantly seeing the following Sagan misquote on this board. Do you think we could stop that?

"The absence of evidence is not evidence of absence."

The absence of evidence is, in fact, evidence of absence. Here's the entire quote:

"appeal to ignorance - the claim that whatever has not been proved false must be true, and vice versa (e.g., There is no compelling evidence that UFOs are not visiting the Earth; therefore UFOs exist - and there is intelligent life elsewhere in the Universe. Or: There may be seventy kazillion other worlds, but not one is known to have the moral advancement of the Earth, so we're still central to the Universe.) This impatience with ambiguity can be criticized in the phrase: absence of evidence is not evidence of absence." - Carl Sagan, "The Fine Art of Baloney Detection", Chapter 12

Other urls found in this thread:

en.wikiquote.org/wiki/Carl_Sagan#Misattributed
en.wikiquote.org/wiki/Talk:Carl_Sagan#Not_Unsourced_-_.22Absence_of_evidence_is_not_evidence_of_absence.22
twitter.com/NSFWRedditVideo

>"The absence of evidence is not evidence of absence."
He's not wrong.

But that's a Martin Rees quote, not Sagan

Source? I can find plenty saying that it's Sagan. Perhaps he borrowed from Rees, but it's most definitely verbatim from Sagan's Baloney book.

What are you on - meth or crack? Try reading (and thinking) before you post.

(Whoops-a-daisy - I should have said: "Perhaps Rees borrowed from Sagan."My life runs backwards in time, apparently, like Merlin.)

>Source? I can find plenty saying that it's Sagan. Perhaps he borrowed from Rees, but it's most definitely verbatim from Sagan's Baloney book.
en.wikiquote.org/wiki/Carl_Sagan#Misattributed

>What are you on - meth or crack?
huh?

Also en.wikiquote.org/wiki/Talk:Carl_Sagan#Not_Unsourced_-_.22Absence_of_evidence_is_not_evidence_of_absence.22

How is that a misquote? He is still taking the stance that absence of evidence is not evidence of absence in that full quote

I get it - you're talking exclusively about the last 8 words of the Sagan quote: "...absence of evidence is not evidence of absence." You're right, that's Rees - good catch. But you're not denying the rest of Sagan's quote, which casts the Rees quote as an appeal to ignorance...are you? If you are, I'll certainly continue to push my central point, and we'll have to get into the nature of evidence vs. proof, etc. Unfortunately, I'm getting a little sleepy here, so won't have a chance to respond for a while.

you have nothing. sagan meant it exactly as quoted. the extra text does not change anything.

Wrong. The absence of evidence IS evidence of absence, and the obverse is an appeal to ignorance. Think, for example, of medical tests. The absence of evidence constitutes evidence of absence (of disease). Not proof, mind you, but evidence. No absurdity exists.

the dictum is wrong, but sagan meant it, OP quote notwithstanding.

so you're saying that because humans didn't have evidence of dinosaur existence 10 thousand years ago, this means that this is evidence for non-existence of dinosaurs?
top kek

Your point is a poorly made, and I'm too tired to parse it. If you're saying what I think you are at first gloss, then do not confuse evidence and proof. Science often has evidence of absence that turns out to be incorrect. Think, for example, of the coelecanth, long thought to be extinct, then discovered alive. The absence of living coelecanth was, in fact, evidence of its extinction, but not, as it turned out, proof.

b-but... evidence and proof are synonyms.....

Thank god (the absence of whom I cannot prove but for which I can present near-infinite evidence) that they're not. Good night all...I'm spent.

>The absence of evidence constitutes evidence of absence (of disease).
You're conflating an absence of evidence with evidence. Doctors perform tests to look for diseases, and so they have gathered evidence. Your hypothetical doesn't have an absence of evidence.

>I invent the cigarrette
>Mm are you sure it doesnt causes cancer?
>Well no studies show it so it means is healthy :^)

>I flip a coin but don't show you it
>you have no evidence that it's heads, so you have evidence it's not heads
>you have no evidence that it's tails, so you have evidence it's not tails

it's true actually
wave function collapse

>absence of evidence is not evidence of absence
No, absence of evidence is not PROOF of absence

I can't prove that there isn't an invisible supernatural Boeing 747 behind me as I'm typing this, but the lack of evidence for it is huge evidence that there isn't one.

>I can't prove that there isn't an invisible supernatural Boeing 747 behind me
just swing a hammer at it

In case of life there's pretty hard evidence: organic material is all over the universe and there's no way around it.

>The absence of evidence is, in fact, evidence of absence

Even in the full quote, this is not what Sagan is saying.

But user, a negative test is evidence of absence.
You're retarded. Go back to wherever you came from.

>The absence of evidence is, in fact, evidence of absence.
t. brainlet

Claiming you can have evidence by doing nothing is lazy science

Then why isn't the quote "An absence of evidence is not evidence?" Clearly the quote is referring to an absence of evidence for a proposition, which is evidence against that proposition.

>Then why isn't the quote "An absence of evidence is not evidence?"
Because an absence of evidence is most frequently misused as evidence of absence, i.e. "we don't know if it's there, so it's not there", not "we don't know if it's there, so it's there".

That would be evidence that it's healthy, not proof.

If evidence is possible one way or the other, then there cannot be a lack of evidence both ways. If evidence is impossible then it is trivially absent.

That doesn't answer the question. "We don't know if it's there, so it's not there" does not imply a lack of evidence. I can have evidence that something is true without knowing that its true.

>If evidence is possible one way or the other, then there cannot be a lack of evidence both ways.
Evidence is possible in the example I gave, you just have to look at the coin. So which evidence do you have?

>Doctors perform tests to look for diseases, and so they have gathered evidence. Your hypothetical doesn't have an absence of evidence.
Such an absence of evidence is impossible if evidence is possible. The lack of some possible evidence for a proposition is evidence against that proposition, thus there cannot be a total lack of evidence for or against a proposition. Your interpretation renders the phrase inapplicable to reality.

>Such an absence of evidence is impossible if evidence is possible.
What evidence does the doctor have before performing the test?

>Your interpretation renders the phrase inapplicable to reality.
You're treating a lack of evidence as evidence, this is what is truly inapplicable to reality.

>Evidence is possible in the example I gave, you just have to look at the coin.
The possibility that I could have looked at the coin is not evidence that it is tails or evidence that it is heads, since the probability of my looking at the coin and observing heads is equal to the probability of observing tails. Evidence would have to favor one over the other.

>The possibility that I could have looked at the coin is not evidence that it is tails or evidence that it is heads
Why can't you determine the coin flip by looking at it?

You mean what evidence could a doctor have before performing a test? The appearance of the patient, the patient's medical history, the incidence of a particular disease in the population, etc.

So if a doctor performs a test, and does not receive a positive result, the lack of a positive result is not evidence? Because the simple lacking of some possible piece of evidence, not the total absence of evidence, is all one needs to illustrate that a total absence of evidence is impossible.

>So if a doctor performs a test, and does not receive a positive result, the lack of a positive result is not evidence?
Why would the result of a test not be evidence?

I'm saying it is evidence, the lack of a specific piece of evidence can be evidence.

>I'm saying it is evidence
Then we agree on that.

So you agree there is no such thing as a total absence of evidence?

>So you agree there is no such thing as a total absence of evidence?
No, I just agreed that the result of a medical test is evidence.

You agreed that the lack of a positive result is evidence of a negative result. Which means that a total absence of evidence is impossible.

>You agreed that the lack of a positive result is evidence of a negative result.
Well yes, assuming the test is binary then the lack of a positive result must be a negative result, so of course it's evidence of a negative result.

>Which means that a total absence of evidence is impossible.
Non-sequitur.

Anything and its absence is a binary relationship. So the lack of a specific piece of evidence is evidence of the opposite proposition. Which means that there is always evidence for or against a proposition as long as evidence is possible.

>Which means that there is always evidence for or against a proposition as long as evidence is possible.
What evidence do you have that the coin I just flipped landed on hands?

You can. If the possible evidence is that we looked at the coin and saw heads, then the absence of this event decreases the chance that we saw heads avid increases the chance that the coin landed tails. If we then consider that we did not look at the coin and see tails, this decreases the chance of tails. If the two events are equally unlikely, the chance of tails is decreased back to its original value.

bump

>the claim that whatever has not been proved false must be true, and viceversa
>viceversa
What Sagan meant with that quote was that there are things we don't know to be true and thus, we should continue to say "we don't know" instead of dismissing them as false just because we haven't prove them to be true. You have shit reading comprehension.