On the nature of evidence

[Skeptic Ginger]

This is something I disagree strongly about i.e. the idea that we can't prove a negative, we certainly can and we often do. For instance "There is no elephant in my room", that negative is very easy to prove, a simple observation proves it and the only way to say it doesn't is to go down the route of "elephant of the gaps".

If something is claimed to be real we can often prove that it can't be. (Not to go down the philosophical route just take "real" to mean anything we can interact with either directly or indirectly.)

I'm in your court here.

THINKING TOOLS: YOU CAN PROVE A NEGATIVE; Steven D. Hales, professor of philosophy at Bloomsburg University, Pennsylvania

If we’re going to dismiss inductive arguments because they produce conclusions that are probable but not definite, then we are in deep doo-doo. Despite its fallibility, induction is vital in every aspect of our lives, from the mundane to the most sophisticated science. Without induction we know basically nothing about the world apart from our own immediate perceptions.
So we’d better keep induction, warts and all, and use it to form negative beliefs as well as positive ones. You can prove a negative — at least as much as you can prove anything at all.

It is useful in science to say one cannot disprove a lot of things. Extraterrestrials comes to mind. But to apply that same principle to the obvious, there is no evidence fairies exist, defies reason.

 

[Skeptic Ginger]

...To state that the side table might be an elephant in someway requires you to provide proof of your extraordinary claim before I need to consider it as even a possibility, given the evidence I have that a side table is not an elephant. ...

Not only that, it requires you to take proving the negative to such an absurd extreme as to make the claim we cannot be sure of anything anywhere at anytime. I don't know about anyone else, but I'm confident saying there is no elephant in my room right now. In fact, it would go against an evidence based world to not be able to make such a claim.

 

[Skeptic Ginger]

Can something only ever be defined as evidence in association with other observations, then? It still seems to be assuming a conclusion and then deciding something is evidence in favour of it, rather than being led to a conclusion through the observations.

How about evidence that you have no opinion of yet? Does that evidence not exist or not become evidence until I draw a conclusion about what it means?

Evidence exists separate from what it is evidence of. Piscivore adamantly disagreed in the other thread. I will have to draw his attention to this one. But the definition of evidence as I showed him in example after example did not include the conclusion one draws from that evidence. You can include the conclusion, but it is not obligatory in defining what evidence is to include the conclusion.

It's a bit like stating a murder weapon is evidence of a particular murder only in retrospect after the crime has been solved. If I have a bloody knife and a man's fingerprints on it, it is evidence of that man having used it to kill somebody up until it has been determined convincingly otherwise.

It is evidence from beginning to end. It is a knife with blood on it. If I am not considering what it means, then, it is a knife with blood on it and nothing more. But the fact I don't know what to conclude from the knife with blood on it does not exclude it from being evidence. That means the conclusion is separate and not needed to define the knife as evidence.

...
Obviously we don't entertain the notion that fairies exist, particularly on flimsy evidence such as somebody saw it. However we could still argue non-parsimonous situations where fairies could exist.

Sure. But that possibility does not make someone's conclusion change the nature of whatever the person was drawing the conclusion from. Whatever it was the person claims was evidence of fairies does not become evidence of fairies simply because magical thinking gets into the picture.

...Why 'rules out'? I'll further dig my grave here by going even more ridiculous - there is no 'ruling out' a Matrix-style universe, other than it being against parsimony. As much as I despise metaphysical notions of laws external to what we can observe, they cannot be ruled out. We don't use them simply because without reason to acknowledge they exist, they are superfluous. However parsimony isn't a universal law - it is a useful assumption about how the universe works.

To say there is no evidence now, does not preclude future evidence.

However, that still not mean observing a fairy is not evidence for one - it just means it on its own will not lead to a conclusion in support of the inference.

If the person did observe a fairy. But you are saying their claim of observing one is evidence they did. Then you try to qualify it by saying the claim is suspect. D'uh, the claim is suspect. It is not reliable at all. The claim is not the evidence, the supposed sighting is the evidence and we don't have that here. All we have is the conclusion.

I agree with all of this except for the last part. Maybe it's just how I've been taught, but I find it difficult to see the merit in starting with a hypothesis which starts with the assumption that something is true. Starting with 'there are no fairies', this is a position which can be falsified. Until that happens, you cannot state either way with 100% certainty. The thing a lot of people trip up on is equating this with the statement 'there could be fairies', which isn't quite the case. Any notion of fairy existence is useless information which cannot be used to make a worthwhile prediction.

But you can state with certainty that the claim of a sighting is not a sighting.

 

[Skeptic Ginger]

...I think part of the problem here is that the statement "I've seen a fairy" is not in fact evidence it's a conclusion; the evidence would be more along the lines of "I saw a little man with wings flying and he turned someone into a toad".

You sir, suffer from a logical mind. I do believe at times it is a curse but mostly it is of great benefit.

 

[arthwollipot]

Not only that, it requires you to take proving the negative to such an absurd extreme as to make the claim we cannot be sure of anything anywhere at anytime.

Why is this absurd? I think it's a perfectly reasonable thing to say. The only thing that we can absolutely state is that we can be reasonably certain of something. Stephen Jay Gould said "in science, 'fact' can only mean 'confirmed to such an extent that it would be perverse to withhold provisional assent'".

I don't know about anyone else, but I'm confident saying there is no elephant in my room right now. In fact, it would go against an evidence based world to not be able to make such a claim.

And I would say that it would be perverse to withhold provisional assent to that statement. Of course, I can't prove that there is no elephant in your room. But I would be willing to accept it as fact, according to the definition above. You probably have better evidence than I, and you can probably state definitively that there is no elephant in your room. But again, you cannot state that as an absolute.

 

[Skeptic Ginger]

....I know fundamentally this is mostly a semantics discussion. We don't disagree on the process. However in communicating skepticism and science, I think understanding the terms and how they should be applied is important.

This I agree with. But dismissing the problem as merely semantics creates as many problems as dismissing the facts in order to use the semantics in a confrontational situation. I suggest separating out the lot here.

Re the semantics, just separate the evidence from the conclusion and all else will follow. If you don't you run into the problem which started this off between Beth and me. The claim was made that believing something was, by itself, evidence of the thing one believed. It was described using the terms here, not sufficient evidence, weak evidence, not conclusive evidence, and Beth added, not evidence of scientific quality.

But my gut, my logical mind, and just common sense said to me magical beliefs are not evidence. So how does one separate magical beliefs from supposed evidence based beliefs? The evidence, obviously. So is the belief, then, the evidence? Of course not. What ever led to the belief is the evidence. So if one experiences something and draws a false conclusion, is that evidence of the false conclusion? No, it is not. Whatever it is evidence of, drawing a false conclusion about it does not make it evidence for the false conclusion.

So how do we separate that out when someone says X is evidence of Y? It's simple, really. Just separate the evidence from the conclusion. And then look at how, when and why you are blurring the two and you will see the error being made.

Now, separate all that from whatever tactics you need to use to address someone with non-evidence based beliefs. That is another issue altogether. You do need to be clear what is evidence and what is a conclusion. But that alone shouldn't stop you from using language that is less than directly confrontational with someone you believe has false beliefs.

...Not necessarily. The term 'evidence' lies at the core of the philosophy of science - hell, people use the term 'evidence' for all sorts of non-materialistic notions. I'm not suggesting that they are practically correct, however we can't afford to simply assume a materialistic philosophy is correct for the sake of randomly choosing a side. We need to consider an observation as evidence for X - regardless of its philosophical position - and then follow this to a conclusion which either supports it or dismisses it.

Just consider that except for quantum mechanics, observations do not change the evidence. Whatever we conclude correctly or incorrectly from the evidence, the evidence is the real Universe. It remains there after our false conclusions and we have the chance to reassess it and draw a more accurate conclusion at any time.

 

[Skeptic Ginger]

Why is this absurd? I think it's a perfectly reasonable thing to say. The only thing that we can absolutely state is that we can be reasonably certain of something. Stephen Jay Gould said "in science, 'fact' can only mean 'confirmed to such an extent that it would be perverse to withhold provisional assent'".

And I would say that it would be perverse to withhold provisional assent to that statement. Of course, I can't prove that there is no elephant in your room. But I would be willing to accept it as fact, according to the definition above. You probably have better evidence than I, and you can probably state definitively that there is no elephant in your room. But again, you cannot state that as an absolute.

I can look around my room and say definitively there is no elephant in here. Yet you want to argue some philosophical principle that is not the case. I will stick with reality, thank you. There is a point where taking that philosophical principle to an absurd extreme becomes as much woo as someone not considering an evidence based Universe.

 

[arthwollipot]

I can look around my room and say definitively there is no elephant in here. Yet you want to argue some philosophical principle that is not the case. I will stick with reality, thank you. There is a point where taking that philosophical principle to an absurd extreme becomes as much woo as someone not considering an evidence based Universe.

Why absurd?

 

[Ivor the Engineer]

I struggling to see how you can separate conclusions from evidence. As soon as you describe an observation you believe is evidence of something, you have made a conclusion that the observation is what you believe it to be.

Without linking an observation to a belief, the observation is not evidence (of anything). It is necessary to make a provisional statement of belief before it is possible to use observations to add or remove support for that belief.

 

[athon]

Skeptigirl, I mean no offense in saying this, but it really would help if you could read through a thread and then form opinions on the views expressed. I find it difficult to read through your responses and pick out the parts I might want to address considering large parts of it have later been clarified, reevaluated or put into better context.

An example is your 'proving a negative' response, which Darat already commented on which led to a further response from me.

By no means am I trying to stifle your opinions on the matter, however it adds little value to the conversation when a number of your points have already been made and addressed by others.

Athon

 

[Skeptic Ginger]

Skeptigirl, I mean no offense in saying this, but it really would help if you could read through a thread and then form opinions on the views expressed. I find it difficult to read through your responses and pick out the parts I might want to address considering large parts of it have later been clarified, reevaluated or put into better context.

An example is your 'proving a negative' response, which Darat already commented on which led to a further response from me.

By no means am I trying to stifle your opinions on the matter, however it adds little value to the conversation when a number of your points have already been made and addressed by others.

Athon

First you complain about people who haven't read every post,

....
I know a lot of respondants have been people who haven't read the thread (and therefore followed its progress), ...
Athon

And now you complain because I went back and read every post.

But the problem here is not what you are assuming. You posted

I'm not sure what you're meaning here, however it might be in hindsight as my wording has evolved through the thread. One of the pitfalls of responding to posts in the sequence of a thread is that they do not take into account the changing of a person's position as they learn more throughout a thread (although I can understand that probably doesn't happen much around here with some people ).

My use of the term 'fairy' in describing an observation is presumptive, and forces the conclusion that this was indeed what they saw. Which is, I concede, incorrect. I would be more correct to state 'a person observes a small flying humanoid traditionally matching the description of a fairy'.

My second error is in the vagueness of the term 'fairy', which is not a concise model describing flying humanoids but rather a varying cultural icon. I was seeking to describe a situation which is not accepted to have any evidence while showing an observation could be made which is technically called 'evidence', even if it is weak and attributable to other rationalisations.

Now, seeing a flying humanoid is most probably due to a hallucination. No argument there. However, to paraphrase, certainty is the realm of religion and politics. We accept that the observation is a hallucination only because it fits perfectly with a number of other observations. However, I suggest it still is evidence for an actual entity external to that person's subjective perception (I hesitate now to use the term 'fairy' for all of its connotations). It is weak evidence which does not shift the conclusion from 'hallucination', however the term evidence can still be applied to it.

To not call it evidence is to risk a circular argument.

'It is not evidence of a 'fairy' because 'fairies' aren't real.'
'How do you know they aren't real?'
'There is no evidence in support of them.'

In reality, applying science (IMO) properly, it is more accurate to say;

'It is weak evidence for a fairy, as there are better models for which it can be evidence of.'

Athon

and

Again, the nature of the language is what gets us into trouble here.

'Proof' is an absolute term with mathematical meaning that is not translated into science at all well. We cannot 'prove' in science; we can only supply sufficient weight of evidence that gives one the confidence to accept one model over another, with view that the provision of new evidence could cause such confidence to change.

By that, I can state categorically that we cannot 'prove' anything about Chester. We can only evaluate the evidence and arrive confidentally at a conclusion on which explanation is most useful.

Athon

while I was replying to the first part of the conversation and because they fell at the bottom of page 2, and my posts continued on page 3, I did not see them until now.

So it may have seemed like I was ignoring your ongoing comments. That is an unfair criticism. You could have asked why I hadn't addressed those 2 posts instead of the comment you did make.

I'll get to them later. This answer used up the time I have right now.

 

[athon]

First you complain about people who haven't read every post,

And now you complain because I went back and read every post.

Um, no. I was 'complaining' that some people comment on earlier posts without being aware of the future responses, which are often significant. By all means read all of the posts. So you should. But I don't see where the use is on commenting on the ones early in the thread when the points you make have already been covered later. You could be saving yourself a lot of time and effort.

But the problem here is not what you are assuming. You posted andwhile I was replying to the first part of the conversation and because they fell at the bottom of page 2, and my posts continued on page 3, I did not see them until now.

So it may have seemed like I was ignoring your ongoing comments. That is an unfair criticism. You could have asked why I hadn't addressed those 2 posts instead of the comment you did make.

Again, my intention wasn't to offend, but simply point out that a) your criticisms (though completely valid in relevance to the post) have been addressed in some part in future responses and b) the thread has moved on. I'm not sure how to address posts which address points of mine which are no longer directly relevant.

I'll get to them later. This answer used up the time I have right now.

Obviously it's simply my opinion on posting style. Feel free to comment on each and every post in sequence, if it makes you happy. But you are a detailed writer (which is a good thing) and it seems to take you a lot of time to address the points. I just think it's superfluous effort commenting when the poster's views have obviously changed as the thread as moved on.

Athon

 

[Dr H]

I'm wondering if some people see the label of 'evidence' only relative to the objective event that produced that observation, while I'm seeing it as relative to all possible events that produce the observation. My problem with the former is that it is not practical, let alone possible that we can know with absolute certainty that an observation is therefore 'evidence'.

OK, I think I see what you're geting at here.

If the evidence in question is the only bit of evidence you have available at the moment, then philosophically speaking I would agree that it is at least potentially evidence for more than one (though perhaps not all) possible event(s) which may have produced the observation.

If on the other hand you do have additional evidence available -- e.g., previous research has been done concerning the existence of fairies, and you are aware of the outcome of at least some of that research -- then the new bit of evidence in question doesn't exist in a vaccuum, but must be evaluated in light of the other evidence already available.

The difference, ultimately, is this - We might agree that observing X is evidence supporting model Y. Another observation, Z, is seen which goes against model Y being true. The observation of Z is stronger evidence.

The former label suggests that X is no longer evidence, as model Y is no longer useful. I tend to think X retains the label of 'evidence', even though it is weak and Y is no longer useful.

I would say that once observation Z shows Y to be untrue, what has been revealed is that the original evidence X had been misinterpreted. X may still be evidence, but at this point you don't know what it is evidence of, other than that is is not evidence for Y, because Y has been disproven.

In other words, once you observe Z, X is no longer evidence of Y, though it may possibly be evidence of something else.

Is this clear, or do I need to think more on my phrasing?

You tell me, after reading my response, above.

The philosophy of skepticism is simple enough to define. However, defining a 'skeptic' is not. To what extent does a person have to apply that epistemology to their decision making to be called a skeptic, for instance? Life doesn't present simple categories of knowledge against which skepticism can easily be applied.

I know I have such an epistemology, however I also know I encounter a lot of decisions where I don't think skeptically, either intentionally or through habits of social thinking.

That's maybe the problem with trying to put sloppy biological beings with fuzzy habits into neat dialectical boxes with sharp boundaries.

It's like trying to determine whether someone might not really be a Catholic because they don't cross themselves when they drive by a church, and don't say 'grace' every time they pop a stick of gum into their mouth--even though the go to church every Sunday, receive the sacrements, and in every other way perform the expected duties of a Catholic.

I'd say it's enough to apply the epistemology to situations in which you are giving serious consideration to important claims about reality. What constitutes "important" may well vary with context.

To paraphrase a discussion from another list, if someone tell's me it's raining outside, I may not always seek out five pieces of objective evidence to support that claim -- I may simply grab an umbrella before I dash out of the house, just in case. I don't think that minor lapse makes me any less of a skeptic, or any more willing to swallow any bit of anecdotal evidence as "truth" without subjecting it to critical examination.

On the flip side (hmm... there's a dated idiom), if someone tells me not to have my child vaccinated against polio because there's a high risk they will contract autism from preservatives in the vaccine, I'm going to want to collect a lot of supporting evidence one way or the other before making a decision on whether to have the kid vaccinated or not.

Likewise if someone tells me "flies come from rotting meat," "the universe is only 6000 years old," or "God said George Bush should invade Iraq", because these are all claims which are in one way or another about the fundamental nature of reality, and such things are important to me.

Ok, cool. We're on the right track then.

Yeah, have to see what can be done about that. ;-)

Now, on that first observation of data suggesting the possibility of a new particle, there would be a number of considerations. Observing the data representing the particle would be evidence for all manner of hypotheses - it is evidence of a mistake,

That's why I inserted the clause "if it were observed many times". If it only happened once, or only 3 times in ten thousand, or something like that, a reasonable conclusion would be that it was due to experimental error.

evidence of a flaw in the method, evidence of a new particle etc. If the experiment is done again and the data is not repeated, then that in itself is evidence in favour of the 'mistake' model explaining the observation, and the previous maths is upheld. Yet I contend that that observation of anomalous data is still evidence of a new particle, even if it is weak and (on its own) insufficient to lend credibility to the 'new particle' model.

I would agree with that under the same conditions I stated above: if that anomalous bit of information was the only evidence at hand. Because if there is strong evidence that the observation was in fact due to experimental error, then you have effectively proven that it is not evidence of a new particle, because it is instead evidence of experimental error.

Well at some stage speculation has to arise, which I guess in some ways has to emerge from little more than the imagination. The vast majority of speculations die at first breath, which is good. I don't think we disagree at all there. But whether the observation that inspired the speculation could be called 'evidence' at all is what I'm contending.

Perhaps what we have is a question of "at what point does information become 'evidence'?"
Evidence is generally assumed to be evidence of something, or evidence for something.

Is a single unconnected observation "evidence" immediately, or does it only become evidence when we start trying to connect it with other observations or information?

Once we connect it to something else, then of course it becomes part of a chain of evidence for whatever it is we imagine that it might be telling us. But a single observation, by itself, unrepeated -- what is that "evidence" of? I suppose it's evidence that 'I think something just happened,' but that seems like a rather trivial case.

The observation has to come first, I agree. I can't possibly imagine how one could seriously speculate anything without an observation to speculate on.

Indeed; I would call that sort of speculation 'creative fiction'.

Interesting point. I'd be more inclined to think that a speculation arises from a single observation initially, which can immediately on further thinking collect more collaborating observations, or 'evidence'. However in itself this is pure speculation - I wonder if there are any psychology papers on the matter.

A single observation, or a series of observations, I agree.

As in my example of demons and the flat Earth, someone may "find" collaboration or corroboration in all sorts of wild juxtapositions if they're relying solely or primarily on speculation and not on a rational plan for collecting hard evidence.

 

[Dr H]

There is a distinction to be made between what is evidence and what does the evidence support. Those are two different things.
{...}
A false conclusion about what evidence means, or what evidence is evidence of, does not change the evidence. (Excluding quantum mechanics for the sake of the discussion.)

You make some good points, including this one, which I tried to convey in my last response to athon.

The act of observing it doesn't change the evidence. Drawing a false conclusion about it doesn't change the evidence.

Good thing you excluded quantum mechanics.

I think where people get confused here is in how they are constructing sentences. But sentences can be properly constructed yet leave information unspoken. If one says they are examining anecdotal evidence of fairies, it sounds like one is saying the anecdotes are evidence of fairies. If you were to write that sentence to include all the information you were leaving out, one would say, one was examining anecdotes which people report believing they saw fairies. We shorten the sentence for convenience but in doing so, one must be careful to recognize you are really examining a report of a vision, you are not really examining evidence of fairies.

I take slight exception here. In the absence of other information the anecdotes are evidence of fairies. They are also evidence that the person(s) relating the anecdotes want you to believe that they observed something which they interpreted as "fairies".

It is only when the anecdotes are examined in light of other available evidence that one can conclude that the "fairy interpretation" is probably incorrect, but the "vision of fairies interpretation" might still be plausible.

I'm pretty sure this is what you were saying earlier in the post, but you seemed to almost turn it around here.

 

[Dr H]

One should be careful here. It seems some people are confusing the validity or reliability of the evidence with the evidence itself.

I think that may be true of 69dodge's "urns" example.

A patient rating pain on a scale is giving direct anecdotal evidence that they are really the only one who can tell you (though there are also objective observations that can be collected as well). In that case we need to use anecdotal evidence in research.
{...}
The conclusions drawn from the anecdotal evidence described above is a separate matter. In medical research we use systematically collected anecdotal evidence and compare it to controls to draw valid conclusions from such evidence.

Some interesting observations on the use of anecdotal reports in medical research. This one jumped out at me: what sort of "control" does one use to determine that a patient is accurately conveying their degree of pain anecdotally?

You cannot conclude a mirage, hallucination, or one's incorrect conclusion about what is observed is evidence of fairies and then say therefore, there is evidence of fairies, it just isn't convincing. Because there is not evidence of fairies. There is evidence people mistakenly assess evidence, but there is not evidence of fairies. It might be tempting to see the semantics here and think, there is evidence, it just isn't convincing. But that is really misleading and comes from the apparent semantics of how we are constructing our sentences.

I disagree here; it is not a matter of semantics, but of context. Is the piece of information being labeled as "evidence" being evaluated by itself, or in the context of other, pre-existing information which also constitutes "evidence"?

If one has no prior knowledge of the state of evidence regarding the existence or non-existence of fairies, and someone reports that they have "seen a fairy," that bit of anecdotal information does, in that context, indeed constitute evidence for the existence of fairies (weak evidence, but that's beside this particualr point). It cannot be determined that the anecdotal evidence has been misinterpreted until and unless it is re-evaluated in the presence of other evidence -- which, in this hypothetical scenario, one does not posess.

I grant that rarely, if ever, would a single piece of information be perceived and evaluated in this kind of isolation, but it is at least theoretically possible -- which is why I stressed that I philosophically agreed with athon on that point.

I also agree with you that semantic carelessness can lead to exactly the sort of problem you describe, but I think that interpretation may be missing the point athon was trying to make.

 

[Dr H]

Which is essentially saying it could be evidence of. It is not saying it is evidence of.

Evidence is evaluated as being evidence within a context. That the evaluation might ultimately be proven incorrect in another context (ie., one in which additional, conflicting information is available) is irrelevant.

I won't go so far as to say that "evidence" is ambiguous, but the concept of "evidence" certainly is not absolute -- it is context-dependent. Information exists, whether we perceive it or not; when we do perceive it, whether or not we call it "evidence" depends on the context in which we decide to look at it.

Information doesn't change, but it's status as evidence for this or that certainly can.

 

[Skeptic Ginger]

Um, no. I was 'complaining' that some people comment on earlier posts without being aware of the future responses, which are often significant.

You are aware of future responses?

I think you meant subsequent responses.

It doesn't "make me happy", however, and I think you may simply not realize that your change in wording does not change my answer.

...I would be more correct to state 'a person observes a small flying humanoid traditionally matching the description of a fairy'.

This still doesn't change what I am saying. Unless the person is lying (and I assume we are not including that possibility here) then they saw 'something'. It wouldn't matter what it was they saw. I agree that whatever they saw was 'evidence'. But here is where we differ. No matter what they conclude about what they saw, their conclusion does not change the evidence.

The fact people believe something is not evidence that something exists. The fact they came to any conclusion based on their misinterpretation of evidence does not change the evidence they misinterpreted.

The wonderful thing about science is that evidence is still there to be reexamined and the evidence is what we go back to again and again to resolve those misinterpretations. But you'll have to read on to understand what I mean here.

We accept that the observation is a hallucination only because it fits perfectly with a number of other observations. However, I suggest it still is evidence for an actual entity external to that person's subjective perception (I hesitate now to use the term 'fairy' for all of its connotations). It is weak evidence which does not shift the conclusion from 'hallucination', however the term evidence can still be applied to it.

It is not weak evidence of fairies. It is not evidence of fairies at all.

To not call it evidence is to risk a circular argument.

'It is not evidence of a 'fairy' because 'fairies' aren't real.'
'How do you know they aren't real?'
'There is no evidence in support of them.'

First off, you do not have the evidence you are calling 'weak evidence'. You have a person's interpretation of some evidence. If you could examine the evidence the person drew the conclusion from, that would be something else altogether. Then you would have 'evidence' but in your scenario, you have a 'conclusion' that someone else formed, you do not have the actual evidence.

In reality, applying science (IMO) properly, it is more accurate to say;

'It is weak evidence for a fairy, as there are better models for which it can be evidence of.'

Wrong. You can say that the individual concluded from some evidence that fairies existed. But you cannot say there is any evidence for fairies, weak or not, because you don''t have that evidence, you only have the conclusion.

Once enough people have examined enough evidence for certain conclusions about the nature of the Universe, we can say, there is evidence for something. If it is 'extraordinary' or new but not enough evidence has been examined by enough people, you can still say there might be evidence or there is weak evidence for something. But for things like fairies, none of the conclusions that evidence exists for fairies have been backed up by producing any of that evidence for others to examine. Now you can say, no evidence has to date been presented for the existence of fairies. So you can make a number of comments about the existence of evidence for a number of things. But you can also conclude there is no evidence for any number of things as well. And in your scenario, you seem to think that is an invalid conclusion. I would answer that logic alone should tell you there must be things for which there is no evidence for the existence of those things.

 

[Dr H]

Seeing a fairy is one form of very weak evidence in favor of the existence of fairies. Stronger evidence would be multiple observations of fairies under controlled, objective circumstances; positive physical testing on the properties of fairies; or perhaps the capture of a fairy which could then be studied physiologically.

Absent any of this additional corroboration, a single anecdotal report of the observation of a fairy would probably be best explained by either non-fiary hypotheses, or if none of those seem to fit all the facts, by treating it as an anomalous occurance, currently unexplained, and waiting for a replication of the observation and additional data.

It isn't 'weak evidence', it is not evidence of fairies by any stretch. The interpretation of whatever the actual evidence is, be it an hallucination or fantasy, does not alter what the evidence actually is. A false conclusion about evidence does not create evidence for the false conclusion.

It is most certainly evidence of fairies in the context presented. The status of information as "evidence" is not determined by the conclusion one may draw at some future date.

Given subsequent data one may determine that the initial evidence wasn't really evidence for the particular phenomenon one originally thought it supported. But in the original context which lacked that additional data, the information certainly was evidence for the given theory, in the given context.

The information isn't altered by the conclusion, but the status of the information as "evidence" is: "evidence" is not an absolute.
__________________

 

[Dr H]

To not call it evidence is to risk a circular argument.

'It is not evidence of a 'fairy' because 'fairies' aren't real.'
'How do you know they aren't real?'
'There is no evidence in support of them.'

Bingo.

In reality, applying science (IMO) properly, it is more accurate to say;

'It is weak evidence for a fairy, as there are better models for which it can be evidence of.'

A quibble: I would say it's weak evidence because it is anecdotal.
Anecdotal evidence is inherently weak because it can be the result of a great number of things which can be difficult to control for: misperception; mistaken interpretation; dellusion; hallucination; deliberate fabrication; etc.

It may also be weak for the reason you cite.

 

[Dr H]

Not only that, it requires you to take proving the negative to such an absurd extreme as to make the claim we cannot be sure of anything anywhere at anytime. I don't know about anyone else, but I'm confident saying there is no elephant in my room right now. In fact, it would go against an evidence based world to not be able to make such a claim.

Oy, are you ever gonna be in trouble when that invisible pink elephant decides to sit down on the same chair YOU happen to be sitting in...