Is Absence of Evidence ever Evidence of Absence?

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Re: Is Absence of Evidence ever Evidence of Absence?

Post by Consul »

Steve3007 wrote: July 21st, 2021, 9:27 am
Consul wrote:In this sense, for example, if there is milk in your fridge, there should be perceptual evidence for it that you can obtain by opening its door and looking inside, since milk is easily visible stuff. And if you do so (thoroughly) without finding any (positive) perceptual evidence for the presence of milk, then this is (negative) perceptual evidence for the absence of milk, and you are thereby justified in believing that there is no milk in your fridge.
This a particular example of a search space (a fridge) which can be exhausted in a very short period of time and an object (milk) that can be unambiguously identified in a very short period of time. Both periods of time are near instantaneous. But not all situations are like that. It doesn't necessarily follow that we suspend belief in those situations. For example, take the proposition that there is an extant "missing link" species between two other species somewhere on the planet. We can (in my view) justifiably believe that the species in question does not currently exist because it has not been found. Obviously if it's found we'll change that belief. Beliefs can and do change in the light of new evidence. But that doesn't stop the belief from justifiably existing now.
All defeasibly, fallibly justified beliefs can become unjustified if new evidence turns up which rebuts or undermines the old evidence. But my point is that it is just not true that absence of evidence is never evidence of absence.
"We may philosophize well or ill, but we must philosophize." – Wilfrid Sellars
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Re: Is Absence of Evidence ever Evidence of Absence?

Post by RJG »

Consul wrote:But my point is that it is just not true that absence of evidence is never evidence of absence.
The absence of X can never be X. The absence of evidence can never be evidence. [~X=X is logically impossible].

In your previous scenario, if your evidence-of-absence = "the non-presence of milk", then what is the absence-of-evidence???
...if you have no evidence, then you have no evidence of anything (including the presence or non-presence of milk).

The absence of evidence can NEVER be evidence of absence. [Logical fallacy is "appeal to ignorance"].
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Re: Is Absence of Evidence ever Evidence of Absence?

Post by Steve3007 »

Consul wrote:All defeasibly, fallibly justified beliefs can become unjustified if new evidence turns up which rebuts or undermines the old evidence.
Yes, or if new evidence turns up where none was there before.
But my point is that it is just not true that absence of evidence is never evidence of absence.
Yes, at least in the sense that absence of evidence for the existence of some thing can be used as a basis for a belief that that thing doesn't exist. As I said, if it wasn't ever used like that then we would indefinitely suspend our belief/disbelief about the existence of an infinite number of possible things. Most people, quite sensibly, don't indulge in that kind of pathological agnosticism. We often hold the provisional belief that things don't exist if we've never yet seen what we regard as evidence for their existence.
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Re: Is Absence of Evidence ever Evidence of Absence?

Post by chewybrian »

3017Metaphysician wrote: July 21st, 2021, 3:10 pm
chewybrian wrote: July 21st, 2021, 2:34 pm
RJG wrote: July 21st, 2021, 7:51 am
chewybrian wrote:I agree with you about that particular reason for denying God, though it begs the question of what a rational argument would be.
There is no rational (logical) argument denying God's existence.

chewybrian wrote:It seems rational to be agnostic…

chewybrian wrote:We can neither prove nor disprove the existence of God, so there you go.
Bingo! ...the belief or disbelief in God takes an act of (blind) faith, either way.
OK, we are on the same page. I know you are the king of logic, and I wondered if you might have an interesting take on that.

Just a footnote if I may. The irony is that the human mind itself (consciousness) can neither be explained rationally, or exist rationally. For instance, the conscious and subconscious mind working together violates the rules of non-contradiction/bivalence in a priori logic; it (the mind) would be considered logically impossible. Metaphorically and Existentially, this is also why human Beings who live life, at some point, usually find life as not just an a or b proposition. It's both. Engineering, on the other hand, is primarily ' a or b ' (apply the wrong formula to the structural beam and it fails-the design is either right or wrong). And in a funny way, this is why some people argue that it is harder for many engineers to be sensitive managers or people-persons. It's not really required for the job.

So, hate to take the wind out of one's sails, but living life isn't all that logical. Unless you believe in a Platonic existence :P
I agree with you if I am following you. Consciousness works both from the bottom up and the top down. It is both determined and free. We don't see how it could be so, and so we generally try to pick one side or the other and fit our understanding to it, ignoring the inconsistencies. My conclusion is that consciousness itself (just the thoughts, opinions, intentions and such) is not material. Of course, I can't prove nor disprove that, just like God, so it's only an opinion. The real answer is that we just don't know.

I was only trying to get an opinion from RJG, because I know he is very locked into logic. I was just curious what he would say.

I think logic is the beginning of wisdom, though it is only as strong as the assumptions to which we assent. When we are young, we get "facts" from our parents and teachers, and it seems the world can eventually be fully understood. Logic follows from the so-called facts, until eventually we arrive at some inconsistencies. We might suppress the problems, or adopt an opposite view from the one provided by the adults, in order to maintain the illusion that we understand what is going on. If you can't break out of the need to know, I think it leads to anxiety, depression and anger, as the world is simply not going to play along with your need. Ultimately, a greater level of understanding (or at least the beginning of wisdom) can be achieved when we admit to ourselves how little we really do know. Then, we can learn how to be better, happier people, to be creative and comfortable in our own skins without the burden of having to try to jamb reality into the box of our preferred understanding.

Logic is a powerful tool for building bridges and such, as you say. It never fails in the "if...then" universe, as long as the "if" is valid. In terms of material objects, we have some very strong "ifs" upon which we can build. But, when it comes to what really matters (happiness, fulfillment, personal growth, empathy...), we don't have that strong foundation upon which to lay the blocks. We have to continue resetting our opinions in these areas, a la Descartes, acknowledging they are always just best guesses. It seems we can make the best progress using both both left and right brain thinking, east and west attitudes, logic and feelings. We just have to focus on the results without getting too caught up on the inability to prove the things that cannot be proven.
"If determinism holds, then past events have conspired to cause me to hold this view--it is out of my control. Either I am right about free will, or it is not my fault that I am wrong."
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Re: Is Absence of Evidence ever Evidence of Absence?

Post by AverageBozo »

The absence of evidence is never ever ever evidence of absence.

Logic does not support the statement “absence of evidence is evidence of absence” as being true.

There is no evidence that supports the statement.

If you like to believe in the non-existence of something, you may do as you like, but know that your belief, supported by neither logic nor experience, is based purely on blind faith.
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