Tuesday, December 06, 2005

Potential- and Actual- Explanation Evidence in Relation to Purely Speculative Explanations

In recent posts I've been talking about purely-speculative explanations, which are meant to be explanations that have no supporting evidence. If the explanation was true then it would account for the phenomenon; except we don't have any independent reason to think that it actually is true.

In the most recent of the posts, I tried to -- amongst some other things -- clarify what I meant by evidence for the explanation. I tried to point out that I meant evidence that shows that this particular explanation, out of all the possible ones, is the actual explanation for this phenomenon; but I wasn't happy with my attempt, and this post is an attempt to further clarify.

In that earlier post, I said

One thing I would try to clarify regarding evidence, is that I mean evidence for that points out that the explanation really is the explanation. I think you can make some distinction between between evidence that it is the correct explanation, and information that makes it appear a good or compelling explanation. Whenever there is some phenomenon to be explained, there are always a number of potential explanations, and evidence for a particular explanation is something that actually points to it as the one that is actually true.

For example, say there is some lettuce on the table has been eaten, and there are a number of possible explanations for this. You might believe that the pet rabbit ate the lettuce, and you might back this up with the claim that rabbits like lettuce. It might be true that rabbits like lettuce, but it's not really evidence that the rabbit actually ate the lettuce. Hmm, I'm not sure whether this example really clears things up, but I don't really have time to try to better what I mean.
I would try to clarify that by saying that there are two classes of evidence: potential-explanation evidence, or evendence indicating that this thing could be an explanation, and actual-explanation evidence, or evidence indicating that this thing is the explanation.

First, I can say what I mean by potential-explanation evidence. For anything to count as an explanation, the very least we need to do is show that it could be a potential explanation. The rabbit eating the lettuce is a potential explanation because we think that the rabbit could have had access to it, and it's the kind of thing rabbits do. As is the explanation that a person saw it and put it in the bin.
On the other hand, there would be some 'explanations' that we would probably say are not even valid as potential explanations. That is, explanations that have no potential-explanation evidence, and that have evidence counting against them. For example, if we said that the flower-vase on the table zapped the lettuce leaf with its death-rays, or that lettuce simply dissapears after more than an hour outside of a fridge. Sometimes it might be less clear cut. For example, the explanation that the dog ate the lettuce leaf, when you know that the dog hates to even touch lettuce.

Potential-explanation evidence says that in principle this thing could be the explanation, but it does nothing at all to diminish the likelyhood of alternate explanations. Saying the rabbit likes eating lettuce makes the rabbit a possible explanation, but it gives you no reason to think that it couldn't have just been a person who came into the room, saw the lettuce leaf and threw it in the rubbish bin.

Actual-explanation evidence gives you a compelling reason to think that the actual case of the phenomenon was one and the same as the given explanation. Actual-explanation evidence is not foolproof, of course. It doesn't show, in any absolute sense, that the explanation is correct. Rather, the distinction between it and potential-explanation evidence rests of the basis of your judgement, or that according to some standard of judgement, and what you think makes something either plausible as an explanation or compelling as the actual explanation. I wouldd say that simply being aware of these two types of evidence can help improve reasoning.

I would note that I don't think the distinction between these two types of evidence is the same as that between direct and circumstantial evidence. Circumstantial evidence can be just as strong as direct evidence, and can provide evidence that an explanation is the actual explanation.

I think the importance of making the distinction between these two types of evidence is this: evidence that something is a potential explanation does not count as evidence that it was the actual explanation, and adding more potential-explanation-evidence does not make it any more likely that it was the actual explanation. We can not say that one potential explanation is more likely than another simply because we have more potential-explanation-evidence for it. We are all familiar with cases where something can seem very compelling as a potential explanation and yet not be the actaul explanation.

Sometimes we have to make decisions based upon incomplete information, where we have little or not actual-explanation evidence, and in that case we may use potential-explanation-evidence. That's okay. But we shouldn't think think that the potential-explanation-evidence is actual-explanation evidence. And I think that's where a lot of people run into trouble. They think that if they accumulate more and more potential-explanation-evidence, they are providing more evidence that the explanation is the actual case.

In relation to the notion of purely-speculative explanations, I mean explanations that have no actual-explanation evidence.

(just a note to remind myself to talk later about the distinction/ambiguity between evidence as facts vs evidence as facts+interpretation)

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