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Author Topic:   If it can be, how can the "Absence of Evidence" be "Evidence of Absence?".
New Cat's Eye
Inactive Member


Message 31 of 309 (533921)
11-03-2009 2:38 PM
Reply to: Message 30 by Rahvin
11-03-2009 2:23 PM


Re: Missing component of the question
What allows you to determine whether there is a pen on the desk?
I think its the "tight definition of the instance".
If you do not observe a pen, there is not a pen on the desk.
But that's not necessarily true. That's why we can't conclude that a pen isn't on the desk soley from the lack of evidence for the pen.
An "empty desk" is the derivative of a lack of observing anything on the desk.
Not just that but going further by observing that there is not a pen on the desk. And we know that because of the "tight definition of the instance".
In this tightly defined case, the absence of evidence is what provides the evidence of absence. But you can only do this with very well-defined terms with a finite scope within the bounds of human observation.
And I think its the "very well-defined terms with a finite scope" that allows for the conclusion and not the absence of evidence.

This message is a reply to:
 Message 30 by Rahvin, posted 11-03-2009 2:23 PM Rahvin has replied

Replies to this message:
 Message 32 by Perdition, posted 11-03-2009 2:48 PM New Cat's Eye has replied
 Message 33 by Rahvin, posted 11-03-2009 2:51 PM New Cat's Eye has replied

Perdition
Member (Idle past 3238 days)
Posts: 1593
From: Wisconsin
Joined: 05-15-2003


Message 32 of 309 (533923)
11-03-2009 2:48 PM
Reply to: Message 31 by New Cat's Eye
11-03-2009 2:38 PM


Re: Missing component of the question
But that's not necessarily true. That's why we can't conclude that a pen isn't on the desk soley from the lack of evidence for the pen.
No, it's not proof, and can't give you 100% certainty...however, it is evidence to be weighed. If your hypothesis is "There is no pen on the desk," one of the predictions of that hypothesis would be not finding evidence of a pen on your desk.
The experiment (looking at the desk) then supports that hypothesis. It's confirmation, but not absolute proof.

This message is a reply to:
 Message 31 by New Cat's Eye, posted 11-03-2009 2:38 PM New Cat's Eye has replied

Replies to this message:
 Message 35 by New Cat's Eye, posted 11-03-2009 3:12 PM Perdition has replied

Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


Message 33 of 309 (533924)
11-03-2009 2:51 PM
Reply to: Message 31 by New Cat's Eye
11-03-2009 2:38 PM


Re: Missing component of the question
quote:
What allows you to determine whether there is a pen on the desk?
I think its the "tight definition of the instance".
And that's only half of it. The tight definition is the definition of what a pen is, and the specific, finite location of the desk that is easily within the bounds of human observation. The tight definition of the scenario allows us to examine every possible location for an object with specific properties.
But it is the lack of observing evidenceof the pen that is the actual evidence for its absence.
quote:
If you do not observe a pen, there is not a pen on the desk.
But that's not necessarily true. That's why we can't conclude that a pen isn't on the desk soley from the lack of evidence for the pen.
But it is necessarily true. Pens are not invisible. We can examine every possible location for the pen because the surface area of a desk is finite and within the bounds of human observation.
If I change the question slightly and ask if a pen has ever been on teh desk, we run into an absence of evidence that is not evidence of absence becasue we cannot examine every point in time to determine whether a pen has ever been on teh desk.
But under the specific question "is there a pen on my desk," an absence of evidence of the pen (the lack of observing the pen on the desk) is evidence that there is no pen on the desk. Again, this only works when we can examine literally every possibility and know exactly what we're looking for. That's why it can't apply to god(s) or ghosts or fairies.
quote:
An "empty desk" is the derivative of a lack of observing anything on the desk.
Not just that but going further by observing that there is not a pen on the desk. And we know that because of the "tight definition of the instance".
You're being pedantic. You cannot observe a negative. That's impossible. You cannot observe a lack of something - its a contradiction in terms. You can only lack an observation - you can have an absence of evidence.
quote:
In this tightly defined case, the absence of evidence is what provides the evidence of absence. But you can only do this with very well-defined terms with a finite scope within the bounds of human observation.
And I think its the "very well-defined terms with a finite scope" that allows for the conclusion and not the absence of evidence.
And again, you're missing half of the problem. The tightly defined terms of the scenario do not preclude a pen from actually being on my desk - the answer to the question could well be "yes" if a pen is actually observed. Within the finite scope of the present condition of the surface area of my desk, there could be a pen or there could not. Only the observation of a pen or the lack of the observation of a pen over the entire surface area can actually allow for a conclusion.
Unless you think you can actually determine whether there is a pen on my desk without even looking? Because that would be the only way you can draw a conclusion from the scope of the scenario without actually making or failing to make an observation.

This message is a reply to:
 Message 31 by New Cat's Eye, posted 11-03-2009 2:38 PM New Cat's Eye has replied

Replies to this message:
 Message 34 by New Cat's Eye, posted 11-03-2009 3:09 PM Rahvin has not replied

New Cat's Eye
Inactive Member


Message 34 of 309 (533926)
11-03-2009 3:09 PM
Reply to: Message 33 by Rahvin
11-03-2009 2:51 PM


Re: Missing component of the question
quote:
What allows you to determine whether there is a pen on the desk?
I think its the "tight definition of the instance".
And that's only half of it. The tight definition is the definition of what a pen is, and the specific, finite location of the desk that is easily within the bounds of human observation. The tight definition of the scenario allows us to examine every possible location for an object with specific properties.
But it is the lack of observing evidence of the pen that is the actual evidence for its absence.
But the simple lack of evidence isn't what allows us to conclude that the pen is not on the desk. Its because we have a tight definition that allows us to determine that the desk does not have a pen on it.
quote:
If you do not observe a pen, there is not a pen on the desk.
But that's not necessarily true. That's why we can't conclude that a pen isn't on the desk soley from the lack of evidence for the pen.
But it is necessarily true. Pens are not invisible. We can examine every possible location for the pen because the surface area of a desk is finite and within the bounds of human observation.
Yes, but also if we are standing here with our eyes closed and haven't really looked for the pen, then we would have an absence of evidence of the pen, but we wouldn't be able to conclude that there is no pen on the desk. We have to have exhausted the search of the desk to conclude that it is void of pens to conclude that the desk doesn't have a pen on it.
You're being pedantic. You cannot observe a negative. That's impossible. You cannot observe a lack of something - its a contradiction in terms. You can only lack an observation - you can have an absence of evidence.
I not just trying to be pendantic. I think I see a real distinction between lacking evidence of a pen on the desk and actually searching the desk for a pen and finding that there isn't one there.
And again, you're missing half of the problem. The tightly defined terms of the scenario do not preclude a pen from actually being on my desk - the answer to the question could well be "yes" if a pen is actually observed. Within the finite scope of the present condition of the surface area of my desk, there could be a pen or there could not. Only the observation of a pen or the lack of the observation of a pen over the entire surface area can actually allow for a conclusion.
But simply not seeing the pen doesn't allow us to conclude that there isn't one there. Maybe we overlooked it or maybe we weren't even looking at all. We have to have looked and found that there are not pens on the desk in order to conclude that there isn't one there. And that is not simply an absence of evidence.
Unless you think you can actually determine whether there is a pen on my desk without even looking? Because that would be the only way you can draw a conclusion from the scope of the scenario without actually making or failing to make an observation.
That's not what I meant. Failing to make an observation of a pen does not allow us to conclude that the pen is not on the desk, we have to have determined that a pen is not on the desk and what allows us to do that is the observation of whole tightly defined scenario.

This message is a reply to:
 Message 33 by Rahvin, posted 11-03-2009 2:51 PM Rahvin has not replied

New Cat's Eye
Inactive Member


Message 35 of 309 (533927)
11-03-2009 3:12 PM
Reply to: Message 32 by Perdition
11-03-2009 2:48 PM


Re: Missing component of the question
No, it's not proof, and can't give you 100% certainty...however, it is evidence to be weighed. If your hypothesis is "There is no pen on the desk," one of the predictions of that hypothesis would be not finding evidence of a pen on your desk.
The experiment (looking at the desk) then supports that hypothesis. It's confirmation, but not absolute proof.
So I state my hypothesis that there is no pen on the desk. Then I stand here with my arms crossed and my eyes closed and viola, I have a lack of evidence for a pen on the desk. Therefore I conclude that there is no pen on the desk.
It doesn't work that way. To conclude that there is no pen on the desk, I have to have evidence of a desk with no pens on it.

This message is a reply to:
 Message 32 by Perdition, posted 11-03-2009 2:48 PM Perdition has replied

Replies to this message:
 Message 36 by Perdition, posted 11-03-2009 3:17 PM New Cat's Eye has not replied
 Message 39 by caffeine, posted 11-04-2009 6:24 AM New Cat's Eye has not replied

Perdition
Member (Idle past 3238 days)
Posts: 1593
From: Wisconsin
Joined: 05-15-2003


Message 36 of 309 (533929)
11-03-2009 3:17 PM
Reply to: Message 35 by New Cat's Eye
11-03-2009 3:12 PM


Re: Missing component of the question
I guess the part of "on the desk" sort of implied looking at the desk.
So then, to be more exact, the prediction would be: "If I look at the desk, I will see no evidence of a pen."

This message is a reply to:
 Message 35 by New Cat's Eye, posted 11-03-2009 3:12 PM New Cat's Eye has not replied

kbertsche
Member (Idle past 2131 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 37 of 309 (533936)
11-03-2009 4:50 PM
Reply to: Message 22 by Coyote
11-03-2009 11:06 AM


Re: Evidence?
quote:
quote:
Anyone who can worship a trinity and insist that his religion is a monotheism can believe anything... just give him time to rationalize it.
Robert A. Heinlein, JOB: A Comedy of Justice
It sounds about as contradictory as the claim that light is both a wave and a particle, doesn't it?

This message is a reply to:
 Message 22 by Coyote, posted 11-03-2009 11:06 AM Coyote has not replied

slevesque
Member (Idle past 4640 days)
Posts: 1456
Joined: 05-14-2009


Message 38 of 309 (533957)
11-04-2009 1:12 AM
Reply to: Message 22 by Coyote
11-03-2009 11:06 AM


Re: Evidence?
I would think this is because the person doesn't know the definition and origin of the word trinity ...

This message is a reply to:
 Message 22 by Coyote, posted 11-03-2009 11:06 AM Coyote has not replied

caffeine
Member (Idle past 1024 days)
Posts: 1800
From: Prague, Czech Republic
Joined: 10-22-2008


Message 39 of 309 (533979)
11-04-2009 6:24 AM
Reply to: Message 35 by New Cat's Eye
11-03-2009 3:12 PM


Re: Missing component of the question
You seem not to be distinguishing between evidence and conclusive proof. Somebody's fingerprints on a murder weapon is evidence for the prosecution, but it doesn't allow us to definitvely conclude they're guilty. A runny nose is evidence for the flu, but not proof. Evidence allows us to increase our confidence, or narrow our uncertainty - as Perdition pointed out, you can have evidence for things that are incorrect. In the case of the pen on the desk, it's always possible we overlooked the novelty pen shaped that looks a bit like a paperweight, but the fact that we can't see the pen is still evidence for its absence. 'Desks with pens on' represent a smaller proportion of the set 'desks on which we can't see pens' than they do of the set of all desks. We have narrowed our uncertainty, so we have evidence that the pen isn't there - even if we're wrong.
Also, there are different kinds of absence of evidence. In your example of being blindfolded and not looking at the desk, you haven't got evidence of anything, certainly. But people don't throw the phrase about only in such circumstances. Usually, people have looked. We may not have the means at our disposal to rule out all possibilities, but if we can think of the evidence an entity or occurence would leave, look for it, and don't find it, we have narrowed our uncertainy and provided evidence for the non-existence of non-occurence of whatever's under discussion. Again - evidence doesn't mean that we've proven it doesn't exist.

This message is a reply to:
 Message 35 by New Cat's Eye, posted 11-03-2009 3:12 PM New Cat's Eye has not replied

subbie
Member (Idle past 1255 days)
Posts: 3509
Joined: 02-26-2006


(1)
Message 40 of 309 (534076)
11-04-2009 8:36 PM


It seems to me that a lot of the disagreement in this thread is due to a fundamental misunderstanding of the nature of evidence and proof.
Absence of evidence is evidence of absence, but it isn't proof of absence. For example, to prove that there are no black swans, we'd need to look at every possible location on the planet that is capable of supporting life in the parameters needed for a swan. If I begin this search in my living room, I have some evidence of the lack of existence of black swans. It's not very compelling, but it is evidence.
This shouldn't be a difficult concept to understand. Scientists come to tentative conclusions based on less than complete evidence all the time. The fact that the evidence isn't sufficient to support a definitive conclusion doesn't mean it's not evidence. It just means it's not conclusive evidence. Thus, the absence of evidence isn't proof of absence, but it is evidence of absence.

Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. -- Thomas Jefferson
For we know that our patchwork heritage is a strength, not a weakness. We are a nation of Christians and Muslims, Jews and Hindus -- and non-believers. -- Barack Obama
We see monsters where science shows us windmills. -- Phat

Replies to this message:
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Domino
Member (Idle past 3958 days)
Posts: 53
Joined: 11-06-2009


Message 41 of 309 (534264)
11-06-2009 11:47 AM


I think the biggest problem here is that we fundamentally disagree on what the definition of evidence is. A dictionary definition of evidence is:
quote:
Facts or testimony in support of a conclusion, statement, or belief.
Key word: facts. Seeing a pen on a desk is a fact about the desk. Not seeing a pen on a desk is a fact about the desk. Seeing that the desk is made out of wood is a fact about the desk. It doesn't matter whether what you see is a "positive" or a "negative"; it's still a fact.
To be considered evidence, though, the facts must be in support of some hypothesis or statement. So if the statement were "There is a pen on the desk," the fact that you see a pen on the desk is evidence for that statement. It is not conclusive evidence, i.e., it does not comprise a proof of the statement that there is a pen on the desk (the viewer could be having a hallucination, or what looks like a pen could really be a paper cutout), but it is evidence all the same. It "tips the scales" towards believing that there is a pen on the desk.
However, if you don't look at the desk, you cannot collect facts about the desk. And so if your statement is "There is a pen on the desk," not looking at the desk means you cannot collect evidence that supports this statement. Therefore, not looking at the desk comprises an "absence of evidence" about the desk. Can you deduce from this that there is no pen on the desk? Of course not! You do not have any evidence to support any statement, so it is impossible to "tip the scales" at all.
So by its very nature, an "absence of evidence" means that there are no facts that will support any statement about the situation. And if you have no facts, how can you draw any conclusions?

"Time is an illusion. Lunchtime doubly so." - Douglas Adams

Replies to this message:
 Message 43 by Rahvin, posted 11-06-2009 12:27 PM Domino has replied

Jumped Up Chimpanzee
Member (Idle past 4942 days)
Posts: 572
From: UK
Joined: 10-22-2009


Message 42 of 309 (534269)
11-06-2009 12:26 PM
Reply to: Message 40 by subbie
11-04-2009 8:36 PM


Dammit
Hi subbie
Dammit, I took the trouble to read all the way through this discussion and thought what a lot of nonsense was being said, and then you and Caffeine ruin my chance of glory by talking some sense.
You are absolutely right to point out that "evidence" is not (necessarily) the same as "proof" and for most of this discussion that has been a point of confusion.
However, I would say that absence of evidence CAN be proof of absence depending on the parameters.
For example, to get back to the original topic and the question of the existence of God, it entirely depends on what the definition of God is. Of course, to my knowledge all religions quite deliberately keep the definition of their God vague so as to ensure that its existence can never be disproven - how can it be if we don't know what we're talking about? But if you were to claim, say, that God is an old man who lives in a particular cave, and you fully explore that cave and find no evidence of any old man, then I would consider that proof of that God's non-existence, as much as anything can be proved.

This message is a reply to:
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Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


Message 43 of 309 (534270)
11-06-2009 12:27 PM
Reply to: Message 41 by Domino
11-06-2009 11:47 AM


Key word: facts. Seeing a pen on a desk is a fact about the desk. Not seeing a pen on a desk is a fact about the desk. Seeing that the desk is made out of wood is a fact about the desk. It doesn't matter whether what you see is a "positive" or a "negative"; it's still a fact.
To be considered evidence, though, the facts must be in support of some hypothesis or statement. So if the statement were "There is a pen on the desk," the fact that you see a pen on the desk is evidence for that statement. It is not conclusive evidence, i.e., it does not comprise a proof of the statement that there is a pen on the desk (the viewer could be having a hallucination, or what looks like a pen could really be a paper cutout), but it is evidence all the same. It "tips the scales" towards believing that there is a pen on the desk.
However, if you don't look at the desk, you cannot collect facts about the desk. And so if your statement is "There is a pen on the desk," not looking at the desk means you cannot collect evidence that supports this statement. Therefore, not looking at the desk comprises an "absence of evidence" about the desk. Can you deduce from this that there is no pen on the desk? Of course not! You do not have any evidence to support any statement, so it is impossible to "tip the scales" at all.
So by its very nature, an "absence of evidence" means that there are no facts that will support any statement about the situation. And if you have no facts, how can you draw any conclusions?
The problem is that the "fact" that I don't see a pen on my desk is actually derived from the absence of any facts indicative of a pen. There is an absence of an observation that matches the characteristics of the pen within the confines of the desk. That is an absence of evidence.
The lack of pen-evidence is what increases certainty that the pen is actually absent. The more thorough the search, the greater the increase in certainty. Since a desk is a finite space easily within the abilities of human observation, a comprehensive search is possible, allowing certainty regarding the presence or absence of the pen to approach unity.
This differs from other phenomenon where a similarly comprehensive search is impossible or impractical. In those cases, the absence of evidence is still suggestive of actual absence, proportional to the amount of searching possible and peripheral evidence.
Searching for god(s) and fairies is simply not possible to the degree of searching for the presence of a macro-scale inanimate object at rest within a specific space. This means that the degree of certainty conveyed by a lack of evidence does not come nearly as close to 100% as the pen search in these cases...but it is a non-zero value.
A true "I don't know, could be either way" conclusion is valid only when no search has been attempted (or is completely impossible) and where no peripheral evidence is available. The number of assertions where these conditions are true is relatively tiny.

This message is a reply to:
 Message 41 by Domino, posted 11-06-2009 11:47 AM Domino has replied

Replies to this message:
 Message 45 by Domino, posted 11-06-2009 1:03 PM Rahvin has replied

Rahvin
Member
Posts: 4032
Joined: 07-01-2005
Member Rating: 9.2


Message 44 of 309 (534271)
11-06-2009 12:31 PM
Reply to: Message 42 by Jumped Up Chimpanzee
11-06-2009 12:26 PM


Re: Dammit
For example, to get back to the original topic and the question of the existence of God, it entirely depends on what the definition of God is. Of course, to my knowledge all religions quite deliberately keep the definition of their God vague so as to ensure that its existence can never be disproven - how can it be if we don't know what we're talking about? But if you were to claim, say, that God is an old man who lives in a particular cave, and you fully explore that cave and find no evidence of any old man, then I would consider that proof of that God's non-existence, as much as anything can be proved.
Quite right - it's the end-point of teh "God of teh Gaps" argument.
If God fills the gaps in our knowledge by filling in that which is uncertain and unknown/unknowable, the final gap to fill is simply to make the God concept itself so poorly defined as to be its own gap.
Asking if there is a pen on my desk is an easy question to answer. But if I ask whether there is a glarnofeeb on my desk...how can you say, if you can't even define what it is you're supposed to be looking for?

This message is a reply to:
 Message 42 by Jumped Up Chimpanzee, posted 11-06-2009 12:26 PM Jumped Up Chimpanzee has not replied

Domino
Member (Idle past 3958 days)
Posts: 53
Joined: 11-06-2009


Message 45 of 309 (534275)
11-06-2009 1:03 PM
Reply to: Message 43 by Rahvin
11-06-2009 12:27 PM


Rahvin writes:
The problem is that the "fact" that I don't see a pen on my desk is actually derived from the absence of any facts indicative of a pen. There is an absence of an observation that matches the characteristics of the pen within the confines of the desk. That is an absence of evidence.
Once again, not looking at the desk altogether results in an absence of facts indicative of a pen, but does this imply that there is no pen? It doesn't. The difference is that when you do look at the desk, you notice not only an absence of facts indicative of a pen, but also the presence of a fact indicative of there not being a pen (namely, the fact that you see an entirely clear desk instead of a desk with a pen on it). But this is all beside the point. It is possible to quibble all day about what comprises evidence and absence of evidence.
Putting terminology aside, I think the question posed by the OP is this: if someone says to you that there is no evidence for the existence of a God, can they then use this lack of evidence as support for the assertion that there is not a God? My answer is that they have to do more than that. Saying absence of evidence about God is equal to evidence for the absence of God is basically saying that God is guilty of non-existence until proven innocent. But it doesn't work that way. God should be considered neither innocent nor guilty until someone can come up with some evidence, and not lack thereof, that can contribute to the question of whether or not God exists.

This message is a reply to:
 Message 43 by Rahvin, posted 11-06-2009 12:27 PM Rahvin has replied

Replies to this message:
 Message 46 by subbie, posted 11-06-2009 1:28 PM Domino has replied
 Message 47 by Rahvin, posted 11-06-2009 1:41 PM Domino has replied
 Message 49 by Stile, posted 11-06-2009 1:55 PM Domino has replied

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