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Author | Topic: Absence of evidence IS evidence of absence | |||||||||||||||||||||||
DNAunion Inactive Member |
quote: No good either. We have no idea what context is involved. Is Sagan, like a lot of the others you quoted, changing the statement by substituting a stronger word - such as proof - for evidence? Is he basically arguing that absence of evidence is not proof of absence? By the way, in case you didn't know this, there's another famous saying associated with Sagan: "Extraordinary claims require extraordinary proof". A claim that life based on silicon exists seems extraordinary to me...so do you have any extraordinary proof? Nah, you don't have any evidence whatsoever. PS: Note that this "Sagan saying" often times appears as "Extraordinary claims require extraordinary evidence". For some nutty reason, some people seem to think that the words PROOF and EVIDENCE mean the same thing, when clearly they don't. [This message has been edited by DNAunion, 11-06-2003]
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DNAunion Inactive Member |
quote: First, not enough context is given to know if they too are manipulating the statement of interest. And when I tried to determine the context, the link you gave did not work (perhaps it will be working later tonight). Second, this is an ASTROBIOLOGY page - those people have an agenda...they have a need to continue to receive funds and lack of any evidence whatsoever is a bit discouraging to those shelling out big bucks. Of course they have a motive for jumping on the "absence of evidence isn't evidence of absence" bandwagon: it's a matter of job survival for them. [This message has been edited by DNAunion, 11-06-2003]
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Dr Jack Member Posts: 3514 From: Immigrant in the land of Deutsch Joined: Member Rating: 8.7 |
The fact is, not finding the contact lens in front of the bar IS evidence for its not being in front of the bar. Absence of evidence is evidence of absence. NO. Not finding the contact lens in front of the bar is not absence of evidence, it's evidence of absence. Reducing to the rather tautological evidence of absence is evidence of absence.
Trying to relate this to the "alien thingy", let's not forget that SETI has been "searching space" for decades without success I think you're rather over-estimating the efficency of the SETI search, it can scan only a tiny, tiny part of the sky at one time, and it can only pick up a tiny portion of potential signals. It's search is more like picking a hundred random grass blades in the football example above.
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Rei Member (Idle past 7013 days) Posts: 1546 From: Iowa City, IA Joined: |
DNA, when you keep on splitting a single topic into many topics, it becomes frustrating to attempt to bother to reply. You've done it so much in this thread that I'm not even going to bother attempting to piece it back together.
Although, I must thank you for stopping the use of the annoying code brackets. ------------------"Illuminant light, illuminate me."
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NosyNed Member Posts: 8996 From: Canada Joined: |
I'm not sure you're right about this Rei. Maybe when a number of separate points are made it is helpful to chop them into separate posts. There is always a chance that any one of them might be the root of a new branch of discussion and posting a reply to the specific one might make it clearer.
Of course, if they aren't really separate then the chopping up makes it less clear as you say. I guess it is a judgement call. Everyone will have a slightly different organizational style. I think you need to be a bit less sensitive to the differences. At least DNA supplies complete sentences and paragraphs. There is a limit to how much presentation style idiosynchracies one can take .
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
Rei/All,
I think there's two scenarios going on here that aren't being separated, & that is the context within which the absence exists. As always, an analogy serves best. That I cannot find my car keys on my kitchen table is evidence that they are absent from the kitchen table. It isn't evidence (trust me!) that they aren't in the kitchen, they're probably on the microwave. The absence only becomes meaningful when the whole picture is being looked at. In science we rarely have the luxury of being able to search the kitchen, & so claiming that the non-existence of something in scenario XYZ is evidence of total absence is flawed. The best that can be said is that isn't where I have searched so far. In fact, logic has a name for this kind of shenanigan, an argument from ignorance; it hasn't been proven to exist, therefore it doesn't. Mark PS Rei, remember that argument over PE we had? Well I'm currently reading The Structure of Evolutionary Theory by Gould, & he admits he was probably wrong to insist on the association between cladogenesis & morphological change. We should give him credit for this almost death bed recantation (it was first published a month or so before his death), I'm glad he wasn't as stubborn as his reputation indicates. It would have saved an hour or so's posting if I'd known that before, anyway! ------------------"The primary purpose of a liberal education is to make one's mind a pleasant place in which to spend one's time" - Thomas Henry Huxley
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DNAunion Inactive Member |
quote: Exactly WRONG. You have materially changed the position: what you knocked down is a mere strawman version of the actual saying "absence of evidence is evidence of absence". I've even pointed out this exact problem (proof or another similar much stronger term being substituted for mere evidence) multiple times in this one thread, and made it clear both in this thread and in the other thread that absence of evidence is NOT PROOF of absence. [This message has been edited by DNAunion, 11-08-2003]
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DNAunion Inactive Member |
quote: I disagree. Looking for them in the kitchen - on the table - and not finding them there is evidence that they are not in the kitchen. It isn't proof, and the evidence may even point towards the wrong conclusion (they very well may be on the microwave), but it is one piece of evidence that supports the position that the keys are not in the kitchen. Also, dragging this back to aliens (I know, this thread is not limited to aliens...), the analogy is weak as it involves searching for something we already know exists. If scientists search Loch Ness for a "monster" and don't find one, is that evidence of absence? And what about flying, pink unicorns? No ones ever seen one - is that evidence of absence? ***************************************
quote: [This message has been edited by DNAunion, 11-08-2003]
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crashfrog Member (Idle past 1467 days) Posts: 19762 From: Silver Spring, MD Joined: |
It isn't proof, and the evidence may even point towards the wrong conclusion (they very well may be on the microwave), but it is one piece of evidence that supports the position that the keys are not in the kitchen. Well, so which then is the more reasonable next step: concluding that your keys aren't in the kitchen because you have one piece of evidence that suggests they aren't; or withholding conclusions until you have more evidence? I'm hoping you chose the latter. That's why we called you on it on the other thread; you were trying to draw conclusions (i.e. an argument of fine-tuning, or that aliens don't exist) while simultaneously admitting you didn't have enough evidence to reach conclusions. I find it rather puzzling, really, that you're so willing to reach conclusions that you admit have no proof.
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DNAunion Inactive Member |
quote: Really? Then you must not be familiar with science. First, have you ever heard that "proof is for mathematics and alcohol". Any idea why people say that??? Second, there are "tons" of conclusions scientists have reached without having proof (obviously) and without knowing for sure that their position was correct. One example that pops to mind immediately....for decades scientists accepted as fact that Universal expansion was slowing over time, yet they had no proof that it was. But did they know for sure that it was? Nope. In fact, somewhere around 1998 multiple evidences by two teams (at least one of which had been studying Type IA supernovae) indicated that universal expansion is doing quite the opposite: accelerating. Another that comes quickly to mind is the dispute over whale evolution: have whales descended from a mesonychian ancestor or an artiodactyl? Back in 1999 (if not still) both sides claimed to have enough evidence to show their position correct and the opposing side's wrong: note that at most, only one of those opposing groups of scientists can be correct: the other team must be wrong. If science actually had to hold off drawing conclusions until proof was discovered, as is in line with your comment, then science would come to a practical standstill. [This message has been edited by DNAunion, 11-08-2003]
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crashfrog Member (Idle past 1467 days) Posts: 19762 From: Silver Spring, MD Joined: |
Really? Then you must not be familiar with science. To the contrary - I assumed that you were familiar enough with science to know that by "proof" I meant what scientists mean: A sufficient weight of evidence. But, perhaps I was mistaken.
One example that pops to mind immediately....for decades scientists accepted as fact that Universal expansion was slowing over time, yet they had no proof that it was. ...because it was predicted by a model that, up till then, had been largely accurate in it's predictions. So now, explain to me again - and this time I'll omit that troublesome word "proof" so that you won't try to prevaricate again - why you think it's appropriate to assume almost total confirmation (leading you to make fine-tuning arguments, among others) given one or two elements of confirming evidence. Basically, I guess my argument is that you're just plain too credulous. Isn't the word "inconclusive" in your vocabulary?
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DNAunion Inactive Member |
quote: Nice spin job. You goofed when you said PROOF, yet you try to turn it around and make me look bad. You're pretty good at playing games, I'll have to admit. ***************************************
quote: [This message has been edited by DNAunion, 11-08-2003]
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DNAunion Inactive Member |
quote: quote: Irrelevant. As I pointed out, they neither had PROOF (the improper term you used) nor did they know for a fact they were correct: in fact, they were wrong. That's how science often times goes, and tentative conclusions abound in science. ***************************************
quote: [This message has been edited by DNAunion, 11-08-2003]
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crashfrog Member (Idle past 1467 days) Posts: 19762 From: Silver Spring, MD Joined: |
As I pointed out, they neither had PROOF (the improper term you used) nor did they know for a fact they were correct: in fact, they were wrong. That's how science often times goes: tentative conclusions abound. What I find most interesting is that you've raised an example about scientists accepting a conclusion without evidence in a discussion that you started about how absence of evidence is sufficient to reject a conclusion. Which is it, DNA? Are we to follow the model of scientists, who according to you, believe things without evidence, or your own example, who believes that an absence of evidence is sufficient to reject any proposition? I'm going to suggest a third possibility: you just believe what you want to believe - what's most inline with your preconceptions. You'll accept an absence of evidence as evidence when it suits you, and you'll reject conclusions based on no evidence when they don't. What I guess we'll never get you to see is that, on the question of the existence of things, a lack of evidence for the positive proposition (that the thing exists) is not evidence for the negative proposition. (There's qualifications to this that I'm willing to make, but they're not relevant here.) Nonevidence can't be evidence. A thing can't be itself and not-itself. But you're trying to add up zeros until you get one. Well, that's fine. I suspect you'll have a lot of fun arguing with Rrhain about it, and I look forward to anytime you two face off. But there's a reason that I don't like to talk to him, and it's the same reason that I don't like talking to you. (No, it's not because you're universally correct, though that's a nice try.)
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mark24 Member (Idle past 5195 days) Posts: 3857 From: UK Joined: |
DNAunion,
I disagree. Looking for them in the kitchen - on the table - and not finding them there is evidence that they are not in the kitchen. It is specific evidence that they are not on the kitchen table, not that they aren't in the kitchen at all. So in the case that involves the entire kitchen where only one part has been searched, absence of evidence isn't evidence of absence. It is evidence of absence as regards the kitchen table, however. I appreciate you aren't making claims of absolute proof, but are making tentative claims as regards the quality of evidence, yet you are unable to make even these claims (in this situation), as I hope to show. The keys are either in the kitchen, or they aren't, they are either 100% there, or they are 100% not there. Assume there are five locations in the kitchen where they might be, the table, the drawer, on the microwave, on the shelf, or in my pocket. In eliminating the table, the keys are STILL either 100% there, or 100% not there. The probability of their existence hasn't dropped to 80%. It is a binary off/on proposition. Therefore, the fact that that they are not on the table hasn't allowed you to make any tentative conclusions as regards the likelihood that the keys are in the drawer, on the microwave, on the shelf, or in my pocket. That the keys aren't on the table isn't evidence that they aren't in the kitchen. Mark ------------------"The primary purpose of a liberal education is to make one's mind a pleasant place in which to spend one's time" - Thomas Henry Huxley
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