Evidence and all that

[chezlaw]

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So if two theories don't make different predictions then they cannot be decided between on the basis of evidence.

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That is where meta-evidence comes in. [img]/images/graemlins/wink.gif[/img]

I guess it depends on why the two theories make the same predictions. If it's because the theories are identical, then one is as good as the other.

But if they are not identical, it's just that they differ only with respect to statements that are not testable, then one can still be right and the other wrong -- although it is impossible for us to determine empirically which (if either)is right and which is wrong.

In that case, I think the meta-evidentiary principle is relevant.

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but no-one ever answers the meta-evidence questions. There are no cases where one of two theories undecidable by normal evidence have been shown to be true, so if you apply meta-evidence you have no normal evidence that the meta-evidence approach is valid.

Hence meta-evidence is a fancy word for something that is not based on evidence.

chez

[maurile]

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There are no cases where one of two theories undecidable by normal evidence have been shown to be true, so if you apply meta-evidence you have no normal evidence that the meta-evidence approach is valid.

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I don't know what you mean by "normal" evidence, but there have been lots of examples of situations where competing theories existed, no experiments had been done to figure out which (if either) was right, and then later somebody came up with an experiment.

The general rule in those situations is that the simpler theory turns out to be the one that is correct. From that we can infer that, in general, simpler theories do better than more complicated theories.

This is not coincidence, by the way. The reason that more complicated theories often fare worse is that the traditional way of making a theory more complicated is to add more stuff onto it. There are more ways to add incorrect stuff than to add correct stuff -- so the more you add, the more likely you are to get some of it wrong.

This is why "the earth travels around the sun" is more likely to be correct than "the earth travels around the sun because it is being pushed by invisible angels." Whenever you add extra stuff on, you are increasing your exposure to potential error.

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That is where meta-evidence comes in. [img]/images/graemlins/wink.gif[/img]

I guess it depends on why the two theories make the same predictions. If it's because the theories are identical, then one is as good as the other.

But if they are not identical, it's just that they differ only with respect to statements that are not testable, then one can still be right and the other wrong -- although it is impossible for us to determine empirically which (if either)is right and which is wrong.

In that case, I think the meta-evidentiary principle is relevant.

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but no-one ever answers the meta-evidence questions. There are no cases where one of two theories undecidable by normal evidence have been shown to be true, so if you apply meta-evidence you have no normal evidence that the meta-evidence approach is valid.

Hence meta-evidence is a fancy word for something that is not based on evidence.

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I don't think this is correct, if I understand what you are claiming. One is using meta-evidence as support for a meta-theory about which of the two indistinguishable theories is likely to be correct. That meta-evidence does not need to arise from observations about indistinguishable theories, though!

Here's a crude example: If I drop a lot of different objects, eventually I will arrive at the theory All Objects Drop. If I then find a new object of a type I have never seen before... I will expect it to drop.

Did I understand your point? Is the above clear?

[chezlaw]

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There are no cases where one of two theories undecidable by normal evidence have been shown to be true, so if you apply meta-evidence you have no normal evidence that the meta-evidence approach is valid.

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I don't know what you mean by "normal" evidence, but there have been lots of examples of situations where competing theories existed, no experiments had been done to figure out which (if either) was right, and then later somebody came up with an experiment.

The general rule in those situations is that the simpler theory turns out to be the one that is correct. From that we can infer that, in general, simpler theories do better than more complicated theories.

This is not coincidence, by the way. The reason that more complicated theories often fare worse is that the traditional way of making a theory more complicated is to add more stuff onto it. There are more ways to add incorrect stuff than to add correct stuff -- so the more you add, the more likely you are to get some of it wrong.

This is why "the earth travels around the sun" is more likely to be correct than "the earth travels around the sun because it is being pushed by invisible angels." Whenever you add extra stuff on, you are increasing your exposure to potential error.

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I agree with all of that but its different. I'm talking about two theories that make no different predictions, not ones that cannot yet be tested.

This is the key I think. Rational belief on the basis of evidence is only meaningful if there is in principle some way of deciding which theory is correct.

chez

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You have artificially constructed a theorem that explicitly refuses to give "evidence" any weight and then reach the unsurprising conclusion that if anyone holds a belief one way or another they cannot do so based on the evidence.

I.e., the conclusion is tautological from your premise that the answer can only be known after we die.

I believe in science. I believe in evidence. I reject your premise.


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The argument is in no way an attack on science, nor is there a trick. I would argue that the proposition E is a foundation stone for science.

What do you mean by you reject the premise. All I'm saying is that two theorems that predict the same evidence cannot be decided between on the basis of the evidence. this is true isn't it? so how could you reject it.

chez

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You call TI a theory, I call it a premise. It can be both. My point remains valid regardless: If you assume away any role for "evidence" then obviously there is no role for evidence. That is not a meaningful proof, it's a tautology.

[chezlaw]

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You have artificially constructed a theorem that explicitly refuses to give "evidence" any weight and then reach the unsurprising conclusion that if anyone holds a belief one way or another they cannot do so based on the evidence.

I.e., the conclusion is tautological from your premise that the answer can only be known after we die.

I believe in science. I believe in evidence. I reject your premise.


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The argument is in no way an attack on science, nor is there a trick. I would argue that the proposition E is a foundation stone for science.

What do you mean by you reject the premise. All I'm saying is that two theorems that predict the same evidence cannot be decided between on the basis of the evidence. this is true isn't it? so how could you reject it.

chez

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You call TI a theory, I call it a premise. It can be both. My point remains valid regardless: If you assume away any role for "evidence" then obviously there is no role for evidence. That is not a meaningful proof, it's a tautology.

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Exactly, I'm amazed how many people want to reject a tautology, I tried to be clear but maybe I failed.

So do we all agree, two theories that make no different predictions about the world cannot be decided on the basis of evidence is a tautology, hence it is true.

chez

[maurile]

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So do we all agree, two theories that make no different predictions about the world cannot be decided on the basis of evidence is a tautology, hence it is true.

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In that sentence, are you using "predictions about the world" as a synonym for "statements of any kind," or as a synonym for "testable predictions."

If you mean "statements of any kind," then the theories are identical -- in which case we don't have two theories, but one (making your claim a tautology).

If you mean "testable predictions," then I will say that, for meta-evidential reasons, "the earth goes around the sun" is more likely to be true than "the earth goes around the sun because it is being pushed by invisible angels" even though the two "theories" make all the same testable predictions.

Theory 1a: Lightning is forged by Hephaestus and sent to earth by Zeus.
Theory 1b: Lightning is an electrostatic discharge... etc. etc. (the details can be easily found on the web).

Theory 2a: Volcanic eruptions are caused by the Goddess Pele using her magic stick Pa'oa and earthquakes are caused by her stamping her feet (both of which occur when she is angry).
Theory 2b: Volcanic eruptions are driven by the ascent of magma.. etc. etc. (the details can be easily found on the web)

Theory 3a: Angels move the planets.
Theory 3b: See Newton, Einstein, etc.

Lather, rinse, repeat.

Suppose that you will grant me that all the 'b's are accepted as true and all the 'a's rejected. Then one could form the theory, based on this evidence, that supernatural agents are unnecessary to explain natural events. On the basis of that theory, we can choose between your god/no god theories...

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In that sentence, are you using "predictions about the world" as a synonym for "statements of any kind," or as a synonym for "testable predictions."

If you mean "statements of any kind," then the theories are identical -- in which case we don't have two theories, but one (making your claim a tautology).

If you mean "testable predictions," then I will disagree and say that, for meta-evidential reasons, "the earth goes around the sun" is more likely to be true than "the earth goes around the sund because it is being pushed by invisible angels" even though the two "theories" make all the same testable predictions.

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I don't think that's what he's saying (not that I'm too clear on it by any stretch), but I think it's basically that if there are two (non-identical) statements about something having nothing to do with the empirical world, then there's no evidence that can be offered for or against either.

E.g.: T1: In heaven all houses are yellow
T2: In heaven all houses are green.

Well then, yeah, I guess he's logically correct that there isn't any evidence that is relevant, but that's because "evidence" connotes an observable fact and his "theories" expressly provide that they have nothing to do with the observable world.

So it's a logically valid, I suppose, it's just meaningless and unhelpful.

[maurile]

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T1: In heaven all houses are yellow
T2: In heaven all houses are green.

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Okay, but in that case the two are equally simple.

If we changed it to:

T1: In heaven all houses are yellow.
T2: In heaven all houses are green and have doorbells that sound like tamborines.

I'd bet on T1 if I had to bet.