Thread: Can they both be rational?

Originally Posted by Alric

If they were robots then they would have the same results. Humans might have the same results but humans are not always rationally and we are very bad at assigning percentages to things. If they were both educated and rational type people, then they should come to the same conclusion but may still have slightly differing percentages because humans are just not that accurate.

Interesting. So you are saying that they would align in their beliefs, if they were truly ideal rational subjects, taken to be really smart, emotionally detached, logical robots.

But wouldn't that mean, if you fed these robots all the evidence in the universe, they'd have the same, single rational view on all ethical, epistemological, ontological, and metaphysical beliefs? This would mean that there is a single rational credence distribution (percentages you assign to each belief) on the set of all beliefs. That would mean there is one rationally permissible perspective on abortion, animal rights, skepticism, religion, which football team is best, et cetera (and it does not and probably should not be the case that each belief in each proposition is with 100% certainty).

You're a bold one.

Originally Posted by Wayfaerer

It seems to me that two rational people could have the same belief graded differently. I'm finding it difficult to imagine one relatively effective method of grading for all proposals.

Bayesianism is p. cool from what I've learned so far. But people still argue about which method for grading is "best." Can you give an example where there are two methods of grading which are equally 'logical', but produce different grades on a belief? The only ones I can think of are the indifference principle, which says that given N mutually exclusive possibilities with no evidence, you should assign 1/N as the likelihood of each possibility. But I reject this idea, because it can produce contradictory belief distributions. (I say instead that there should be no distribution assigned in that case, but some people disagree with me on this).

Another debate deals with how to use correlative evidence when forming beliefs about action, and it is at ends with a causal evidence approach. I could explain why I like the causal approach more and what they both are if you'd like.

Point being, I can see how you could have a single best way for assigning credences. I find it possible to imagine multiple best ways, but I find it harder to justify this possibility... I have yet to come across two ways to grade that are equally compelling.

Each article of evidence could 'reasonably' carry different weights for different people, especially since they only really serve to help you effectively guess in the face of the unknown.

How?

Some people might be guided by one possibility over another for aesthetic reasons.

Inherently, aesthetics don't justify belief in jack, so these people would not be rational.

A good example might be the proposal of the planet Vulcan to explain Mercury's disagreement with Newton's laws of gravity. Would all rational people have to have been 99% sure that it existed considering all the evidence supporting Newton's laws? After a time of never being able to find Vulcan, would someone who was 80% sure that a big conceptual leap in how we think of gravity was needed have been relatively irrational?

You're example is not clear. 99% sure that Newton's laws exist? Or that Vulcan/Mercury exists? Do the Vulcaners believe in them, or the Mercurians? What is this "relatively irrational" you speak of? If group A had evidence for the laws that group B didn't, then it's of course permissible that the rational group Aers differ in their beliefs from the rational group Bers.

Nature has presented us with many unexpected observations in the past that it would be hard to say for sure. It could have been invisible matter perturbing Mercury's orbit for all they knew.

I have no idea what your example is talking about at this point.

Individually proceeding from this information seems more of an intuitive procedure, guided by aesthetic preferences of different ideas. A similar situation going on now with galaxies showing departures from general relativity could be seen the same way. Some seem 99% sure that "dark matter" exists, some aren't so convinced and give more consideration to the possibility that a reworking of gravity might be needed. Both of these possibilities seem rational, especially considering the previous example. Some of these people might just be guided by hunches that evidence can't support yet.

Aaaand I have already commented on some things covered in here, and won't argue with your conclusions until you've clarified some things.

Also, lol @ this thread:

If you don't like assigning a single degree of certainty to a proposition, pretend you're assigning a range of degrees instead. I have 80%-90% confidence that it will rain tomorrow.

Reformulated this way, the strong version of "single rational credence distribution" would say that the ranges would have to align. (A weak version would perhaps allow for a mere overlap between two rational people's ranges. But the weak version isn't very informative, if for example one person had a range of 0-100% in the proposition "the sun will explode tomorrow", and the other had a range of .001-.00101%. Would those two people be equally rational?)