The Antecedent Probability Principle, the Proportional Principle & Carl Sagan

Or why we can never believe in miracles.If you tell me that there is a statue in a church of the Virgin Mary it is rational of me to accept your assertion because my life experience tells me that this is quite possible - statues often hang out in churches. If you have no history of lying to me randomly about everyday events and there is no other reason to suspect that you could be mistaken there is no logical reason to doubt you.This is the Antecedent Probability Principle. I accept what you tell me because it lies within what I know to be probable.If, however, you also say "and it's hovering 6 feet off the floor" I then have cause to doubt. I know from experience that statues don't hover and that there is a greater likely hood of your assertion being false - for whatever reason. If I am to behave rationally I must assume you are mistaken.In order for me to believe you I then need far more evidence than normal. What is happening here is that I proportion my belief in what you have told me in relation to the net evidence for it. The more rationally unlikely the event, the more unlikely it is to be true and the more evidence is therefore needed for it. This is the philosopher’s version of Carl Sagan’s argument that extraordinary claims need extraordinary evidence.If someone chooses to accept weak evidence for extraordinary events above their known experience of the physical world they are therefore thinking irrationally.However, it may be that the hovering statue is still hovering, in which case you can go and test it so that the standard of evidence matches the scale of its improbability. If after doing some simple tests yourself it would then be rational to believe that some miraculous intervention is occurring.But note, while it may well be rational to think that way, it may still be an error as it may be that your understanding of the phenomena is just incomplete.To give an old example, a solar eclipse would seem miraculous if you hadn't lived in a culture that has the science to understand it.Also, the fact that you have done some tests that convinces YOU, it does not mean that when you tell someone else that it is rational for THEM to believe you. They may take note of what you say, take your tests into consideration but still reject it because they rightly need more objective analysis if they cannot witness the event themselves.And so on.The logical conclusion of this argument is that miracles cannot exist. This is because the more extraordinary the event, the less credible it must be, and as a miracle defies a natural law - which is impossible - they therefore cannot exist.I'm sure this begs the question. Maybe someone who has properly studied this can take the argument further?

Mr Jack, NoNukes, nwr, JohnWe seem to be agreed that it can never be rational to accept a miracle because we can never get to the necessary level of evidence.Even so, miracles could still exist, it's just never rational to believe in them.Ok. But that sounds like 'we can't logically rule it out, but given the arguments so far, plus what we think we know of the world, we think it so bloody unlikely that we might as well say, "stuff it, for all practical purposes they can't exist"'Taking it to the next step and ruling miracles out completely, requires the moves1. a miracle defies natural laws
2. Natural laws are all there are
3. Miracles can't existBeing pragmatic, I'll happily accept 2 at face value, until proven wrong.But hang on, as it's never rational to believe in miracles, I can never be proven wrong.......Edited by Tangle, : Typo

It's irrational to accept a something without evidence is it not? It may be human to do so and it may be ok to do so, but strictly speaking, it would be irrational.

that would be why I said this I suppose: Followed by this: Our understanding of nature's laws ARE incomplete and will always be so. It follows then then we can never say that anything is miraculous because of that same fact. If a limb ever does grow back spontaneously, we can never say that it was a miracle because we can never be sure that there's not a natural process that could do it.But we both know it's not going to happen.

By the time I was old enough to understand the concepts you mention - hot, iron, don't etc, I had had overwhelming evidence that my mother was trustworty. i don't think so, but it does seem to be a bit binary for some people. If you call someone irrational its an insult, but it rather depends on the context; no-one wants to be Spock either.

That's a really odd question. Surely it doesn't matter whether it was or whether it wasn't but in either case we can't know? It presumably seemed like a worthwhile and rational activity to him and presumably he had enough evidence to convince himself that it was worth continuing.Happily, not everything we do in life needs to be strictly rational, if only to keep the economy moving - why else would I be reaching for my golf clubs now?

Agreed - 2 is an unproven premise.I'll still take it as true until proven wrong and I claim that it is rational to do so.

I used 27 words to expound my point at 'length' which is roughly 60 less than you've used to tell me I shouldn't have done it. I win in the war against verbage.But of course, you've missed the point.NoNuke was trying to say that it's irrational to follow your mother's advice because it's unevidenced by you personally. I was saying that it is highly evidenced because my previous experience has told me that I can trust my mother in matters that I don't understand yet. Therefore it is totally rational for me to do what my mum says.

I'm not ducking the question, I'm say that the question is irrelevant.I don't care whether Einstein was behaving rationally when he spent ten years working on relativity or not - I do care whether the result of his work is rational because I need to trust it for my sat nav.You may have gathered that I don't think it matters whether people behave rationally or irrationally until it actually DOES matter. One place where it matters is when we're trying to understand facts about the world.

I've no idea. But the search for whether they exist is rational. I agree entirely and I'd say that that is one of sub-clauses of the antecedent probability principle - We're forced to accept conclusions or actions based on best prior knowledge and reject actions that have the least convincing evidence.

They accept biblical (and other) miracles based on unevidenced beliefs. That is irrational. The distinction is largely irrelevant as we can't even trust the accounts of the miracles to be accurate. But to take one from the NT at random, the raising of Lazarus either didn't happen or could be explained naturally - pick one, most disbelievers wouldn't care which. We have no evidence for any of it so the only rational position is to be totally skeptical.

Well as a trivial point, we obviously know string theories exist. What we don't know yet is if they are correct. So it's rational to work further to see if they are. Why stick to those two theories? I'm happy to say that the search for knowledge about our world is always rational and seems self evident - it's on you to say why it isn't.

No, I don't think that at all.For example, I don't think that the search for the ark on Mount Arafat is rational because we have no evidence that the ark ever existed and huge quantities of evidence that says it doesn't.But to be consistent, I would say that if an irrational person ever searched for the ark and found what could be its remains, it would be vaguely rational to properly test it because there would then be some evidence worth testing.I think that reasearching String Theory is rational because there's a logic basis for the investigation. I answer that in the origianl post.

Then perhaps you could explain what point you are trying to make, because I'm completely missing it at the moment. Obviously.

er, I AM saying that it's rational to research string theory and any other evidenced based subject.That's all I've ever said, so I'm still confused as to what YOU are saying.Edited by Tangle, : No reason given.