Absence of evidence, and evidence of absence

@Zetherin,

Zetherin;98978 wrote:

Well, I can't help but agree with:

I think that is true too. It seems as though one would have to go case by case.

I think your unicorn example proves true - the absence of evidence is evidence of absence. But there are many creatures with which we have had an absence of evidence, but it wasn't evidence of absence. X seems as though it would have to be really possible, and not just logically possible (a unicorn is logically possible, but not really possible). For instance, we discover a few new species of fish every year. We wouldn't say the fact we have an absence of evidence for these new species as evidence for them not existing, would we?

But say I conjure the idea of a Hampherfish right now. I describe it's qualities and I even make it fit specie(lly) into a scientific model. I design it so that it has place in the theory of evolution. There currently is absence of evidence. Beyond all reasonable doubt, is the absence of evidence, evidence of absence, in this case? Does the fact that I designed the fish to be really possible and not just logically possible make a differnece?

It certainly does make a difference. To say of something that it is logically possible (its supposition is not self-contradictory) is no evidence that it exists. But to say that something is a real possibility (more than just logically possible) is to say there is some reason to think that it exists.

That we have sufficient evidence for the existence of something does not entail that that something exists; only that our belief that it exists is justified. Our belief that there were WMD's might have been justified (whether is was is a different question) but it still might have turned out that there were none. Justification does not guarantee truth.

@kennethamy,

kennethamy wrote:

It certainly does make a difference. To say of something that it is logically possible (its supposition is not self-contradictory) is no evidence that it exists. But to say that something is a real possibility (more than just logically possible) is to say there is some reason to think that it exists.

But the fact that it could really exist isn't evidence that it exists either. To say something is really possible is saying that there is some reason to think that it exists? Isn't it saying there is some reason to think that it may exist, not that it exists?

Quote:

That we have sufficient evidence for the existence of something does not entail that that something exists; only that our belief that it exists is justified. Our belief that there were WMD's might have been justified (whether is was is a different question) but it still might have turned out that there were none. Justification does not guarantee truth.

Good point regarding the justification of belief.

@Zetherin,

Zetherin;98983 wrote:

But the fact that it could really exist isn't evidence that it exists either. To say something is really possible is saying that there is some reason to think that it exists? Isn't it saying there is some reason to think that it may exist, not that it exists?

Good point regarding the justification of belief.

It is both. Depending on the strength of the justification. That a substance looks like gold is evidence that it is gold. Just not very strong evidence. But, of course, it depends on the context. If we know there is a lot of iron pyrite in that area, then that the substance looks like gold is very weak evidence for its being gold.

@kennethamy,

truth, justified belief, rational speculation, imaginary construct?
The relative roles of reason, experience and evidence?

@prothero,

I suppose I could make the argument that kennethamy's intent in starting this thread was to instigate a heated debate about WMD's and the invasion of Iraq.

If I were to state my argument, it would go like this:

1) Donald Rumsfeld was one of the architects of the war in Iraq.
2) Donald Rumsfeld made the statement that "absence of evidence
is not evidence of absence," in respect to the search for WMD's
in Iraq.
3) Some people on this forum are opposed to the war in Iraq, and believe
that the invasion was launched under false pretexts, and would immediately
focus on this aspect of the original post.
4) Kennethamy is aware of 1, 2, and 3.
5) Kennethamy originated this thread by quoting Donald Rumsfeld.
6) Therefore, kennethamy purposely quoted Donald Rumsfeld with
the intention of stirring up controversy.

A similar argument could be put forth that kennethamy wanted to start a heated and controversial thread debating the existence or non-existence of God.

Though my premises are most likely true( although 4 may be debatable), I have reached my conclusion through inference rather than by what logically follows, or deduction. I could say that my conclusion is logically possible, but that does not mean that the intent exists, or that my statement is true.

But, then again, perhaps kennethamy just felt that Rumsfeld's statement was an interesting exercise in logic, and was curious as to what other forum members would make of it. That is, the evidence of an intent to create controversy, which I am supposing in my premises, does not prove any actual intent.

Even asking kennethamy what his intention was would not necessarily bring out any sort of truth, as he could lie about his intent for a number of reasons. Do I have any evidence of this? Nope, but the absence of evidence (that kennethamy would tell a lie) is not evidence of the absence of his ability to tell a lie.

There is, however, overwhelming evidence that I don't know what the heck I'm talking about and am just rambling on brainlessly at this point, but I'm going to post these thoughts anyway because if I'm way off base in my thoughts I'd like to be shown the correct path to the base.

TTM

@kennethamy,

What we would like to be "true," we attempt to "prove." What we would not like to be "true," we attempt to "disprove." We want to believe what makes us happy and disbelieve what makes us sad. Sometimes we have to believe something unpleasant because this belief will protect us from something even more unpleasant.

We are not cold calculators. We are more like the well-paid lawyers of our fantasies.

@Reconstructo,

Reconstructo;114729 wrote:

What we would like to be "true," we attempt to "prove." What we would not like to be "true," we attempt to "disprove." We want to believe what makes us happy and disbelieve what makes us sad. Sometimes we have to believe something unpleasant because this belief will protect us from something even more unpleasant.

We are not cold calculators. We are more like the well-paid lawyers of our fantasies.

Not at all. The mathematicians who finally prove that the circle could not be squared didn't care whether it could or could not be squared. They just wanted to be able to show whether it could be squared, or whether it could not be squared. But even if you were right, what would that have to do with the actual proof? People may very well prove something they hoped would not be proved. As when the police prove that someone who is missing is dead. Or if an accountant proves that his business is going bankrupt.

@kennethamy,

You mention the cases where proof is more practically attainable. I agree with you on those. But how does one prove that life is worth living? Or that one is a good person? These are vague but important issues for human beings. How is one convinced that a woman is worth a wedding ring?
They wanted to prove the circle could not be squared for the glory of it, I would think, as well as out of curiosity.
Yes, sometimes we prove what we don't want proven. Humans are complex. I just wanted to emphasize the importance of motive.

@Reconstructo,

Reconstructo;114763 wrote:

You mention the cases where proof is more practically attainable. I agree with you on those. But how does one prove that life is worth living? Or that one is a good person? These are vague but important issues for human beings. How is one convinced that a woman is worth a wedding ring?
They wanted to prove the circle could not be squared for the glory of it, I would think, as well as out of curiosity.
Yes, sometimes we prove what we don't want proven. Humans are complex. I just wanted to emphasize the importance of motive.

You did not say that you were talking about matters to which the notion of proof is not applicable. But then, what you say about proof is simply irrelevant to those matter, so I don't know why you said it.

@kennethamy,

I have my reasons. How does one prove the correspondence theory of truth? How does one prove that proof is valuable?

@Reconstructo,

Reconstructo;114780 wrote:

I have my reasons. How does one prove the correspondence theory of truth? How does one prove that proof is valuable?

John Stuart Mill writes the following in his great essay, Utilitarianism.

There is a larger meaning of the word proof, in which this question is as amenable to it as any other of the disputed questions of philosophy. The subject is within the cognisance of the rational faculty; and neither does that faculty deal with it solely in the way of intuition. Considerations may be presented capable of determining the intellect either to give or withhold its assent to the doctrine; and this is equivalent to proof.

We can present such "considerations" "capable of determining the intellect" with regard to the correspondence theory, and even to the other question.

@kennethamy,

Good answer. Sounds like persuasion.

@Reconstructo,

Reconstructo;114790 wrote:

Good answer. Sounds like persuasion.

It isn't. It is what has also been called, "reflective equilibrium".

Reflective Equilibrium (Stanford Encyclopedia of Philosophy)

@kennethamy,

How very Rorty that sounds! Same deal for me. You persuade by appealing to the person's previous beliefs/values. It's a matter of terms.

@Reconstructo,

Reconstructo;114798 wrote:

How very Rorty that sounds! Same deal for me. You persuade by appealing to the person's previous beliefs/values. It's a matter of terms.

If you read further into the article, the author talks about Rorty at length. My view is that "even a stopped clock.....".

@kennethamy,

I wonder what you would have to say about page 93. Objectivity, relativism, and truth - Google Books

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Absence of evidence, and evidence of absence

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