Of course it does. Absence of evidence is only irrelevant if there is no practical way to get evidence. The “kinds of debates” you’re talking about are usually explicitly framed to exclude any expectation of evidence. That does not mean that absence of evidence is irrelevant for the cases where you would expect evidence to be found.
You can repeat that all you want but I’m not sure what you mean by it. Do you agree or not that in that situation it is reasonable to reduce the probability of the existence of the cat based on the lack of evidence as provided or not?
I also think it’s pretty ironic that someone who wants to stick to such a strict definition of “evidence” would blithely claim there is ANY evidence there’s no elephant in their room. What about a really small one? There’s no evidence elephants can’t be microscopic, after all.
Let’s rephrase this: You look around the room and your senses do not provide evidence of the existence of elephants in the room. The question of the OP: Is that evidence that there are NO elephants in the room?
This is becoming boring. Do I really have to do a step-by-step explanation for you?
It’s almost as obvious to me that if “absence of evidence” really signifies nothing it would be useless to do blind tests on medicine or any other subject.
What??? We are testing whether or not a lack of evidence of “x” is evidence that “x” does not exist.
“Evidence” does not equal “lack of evidence.”
My comments to Anduril cover this.
We are debating whether a lack of evidence of “x” is evidence that “x” does not exist.
Fact is…it is not.
When I say “a lack of evidence of “x” is not evidence that “x” does not exist…I mean….a lack of evidence of “x” is not evidence that “x” does not exist.
In a real sense, NO. Your hypothetical is off target. Consider the question: What is the “x” being tested in your hypothetical…the “x” for which you assert there is no evidence?
While thinking about that, consider my hypothetical:: We have absolutely no evidence whatsoever that any life exists on any planet circling the nearest 5 stars to Sol. Do you consider that in any way evidence that there is no life on any of any of those planets? Or do you consider that merely evidence that we do not have any evidence of life on any of those planets?
I will gladly and freely acknowledge that the lack of evidence that there are no microscopic elephants in the room is not evidence that there are no microscopic elephants in the room.
Nah, x is: ‘there is an elephant in this room’. You look around, see no elephant; hence, there’s absence of evidence for the truth of x. If absence of evidence were not evidence of absence in this case, that would mean that in your assessment of x, nothing ought to have changed after you have looked around; you still have as much grounds to reject as to accept it. Obviously, nobody really thinks so – thus, most people conclude that absence of evidence for the existence of an elephant in the room constitutes evidence of said elephant’s absence; and it’s reasonable to do so, since ‘there is an elephant in the room’ is a particular statement – a singular existential, a little more formal something like ‘there exists x, such that x is an elephant, and x is in this room’ – which is perfectly well decidable through finite observation; only universal statements, like ‘all elephants are in this room’ – ‘for all x, if x is an elephant, x is in this room’ – aren’t: there could always be another elephant not in this room, and all absence of evidence for outside elephants can’t decide the matter.
Or, for a different hypothetical, let’s say you postulate a fifth physical force. As a consequence from its behaviour, in a certain particle interaction a certain particle ought to be created (let’s call it the x-particle). So, you set up your experiment to perform the interaction, but fail to detect the proposed x-particle. That means you have an absence of evidence for x-particle production, and, since x-particle production follows necessarily from your theory, you better should revoke it. In this case, absence of evidence (for the x-particle) is, again, evidence of absence (of the fifth force).
x = “these people own a cat”. I thought that was obvious.
Consider this: let’s say there IS life on any of those planets. What kind of evidence can we, right now, find that would lead us to conclude it’s there? We can only barely detect planets at all so we might miss more than a few of them, and the only detection we can practically do is a tentative spectroscopic analysis of the atmosphere.
I submit that in your hypothetical scenario, we can attribute any absence of evidence to our inability to look for the evidence, and that’s the reason we can’t make any meaningful inference from it. The lack of evidence for life on the moon, for example, is much more meaningful.
Seems to me you’re trying to keep a strict linguistic / logical interpretation where “absence of evidence” is tautologically not “evidence”. But the statement “absence of evidence is not evidence of absence” doesn’t work that way: it means “absence of positive evidence for the existence of something isn’t meaningful” and I’m arguing that that’s just not true in most cases.
There is a huge difference between “evidence of a lack”…and a lack of evidence.
You might want to consider that or a bit and rethink your argument here. I’ll get back to you more thoroughly on it (got lots to do for the next two hours)…but your reasoning is very faulty because of that difference.
A lack of evidence for “x” is not…and never will be…evidence that “x” does not exist.
You claim that not detecting an elephant in your room is positive evidence for the non-existence of an elephant in your room. You also claim that this doesn’t violate your argument for some reason since this failure to detect the elephant is - again for some reason - not absence of evidence for the existence of that particular elephant.
All the evidence for the existence of the elephant is absent. You’ve seen no elephant, you’ve not detected any elephant droppings, there isn’t a large suspicious shape under a sheet somewhere and you hear no trumpeting. Yet this is according to you not “absence of evidence”.
Let’s expand the area a bit. Now let’s say you want to see if there is an elephant in your house. Start with your room; no evidence. Walk to the next room; again, no evidence. etc. Would you consider this lack of evidence for the existence of the elephant? If not, why not? Would you consider this evidence against the existence of that elephant? If so, why?
Now switch to an apartment building and repeat the exercise.
How large does the area have to be before you switch to the position that there is now suddenly no evidence at all (for or against)?
Beyond this, we can create situations where we would expect to see evidence if the theories did work, such as collecting information about those born under given signs and comparing different classes. Theories get falsified all the time by absence of evidence against the null hypothesis.
Let’s not bother talking about proofs. Whatever problems we have with the claim we are discussing, it does not mention anything about proof of absence, only evidence of absence. The number of white swans you’ve observed, and the geographical distribution of the observations, increases the probability that there are none. But doesn’t prove it.
Yes. The “problem” is that you cannot have any direct positive evidence of the non-existence of anything. The best you can ever do (unless the item in question is logically impossible) is try to get evidence for its existence. The “debate” is whether you can ever say that having failed to find evidence should influence the probability of the item (not) existing.
So far, the only person in this thread who claims it’s not possible to do that has shown a remarkable flexibility in the definition of “lack of evidence”, some plain assertions, and not much else.
Unless Frank comes back with a clearly reasoned argument, I consider the matter resolved.
First, are you confusing things that would contribute to a proof of nonexistence with things that are just evidence of nonexistence? The logic I know of does not discuss evidence.
Second, do you really not see the difference between expected and unexpected evidence? We can consider the things beyond which we know nothing as a kind of event horizon. At the moment, I have no evidence for or against the contention that my brother in Boston had eggs for breakfast. The absence of evidence for this says nothing about the truth of the proposition, because it is outside my event horizon. However, the absence of eggshells in the trash is evidence that my wife didn’t have them. Not proof - evidence.
I’m responding to posts in order, so maybe sometime later someone has helped you with this point.
The point being the difference between a “lack of evidence” and “evidence of a lack.”
The fact that you look around and see no elephants (I am leaving aside your microscopic elephants or invisible elephants)…is evidence that there are no elephants.
We are not working with a lack of evidence here. We have evidence…it just happens to be evidence that there are no elephants in the room.
This is quite different from the question of whether or not there is life on any of the planets revolving around the 5 nearest stars to Sol…where we have absolutely no evidence in either direction.
The “evidence of lack” (which IS evidence) is what persuades me there are no elephants in the room…not any lack of evidence.
I am sorry you are having so much trouble with this.
Wikipedia, which I hardly ever cite, does an excellent job of discussing the lack of evidence fallacy…which is often called the argument from ignorance or the argumentum ad ignorantiam. You might want to read it.