Saying that X asserting A provides very weak evidence for A should not be confused with saying Y asserting B provides evidence for not-B. One claim is about magnitude while the other is about sign. In most situations, the latter commits one to violating conservation of evidence, but the former does not.
No, if you learn first that X is being claimed, then you learn that many people claim it for stupid reasons, then after learning the second fact your confidence in X goes down, as in this example:
learning that many people believed in an Australian-Zulu connection for religious reasons decreases my probability that the posited Australian-Zulu connection is real.
There’s no violation of confirmation of evidence: not learning today that a particular religious tribe believe in an Australian-Zulu connection increases my confidence in the proposition by a tiny amount, just as Barack Obama not walking through the door right now decreases my confidence in his existence.
Barack Obama not walking through the door right now decreases my confidence in his existence.
He’s insanely unlikely to walk through my door, but if after all the evidence he manages to not actually exist, the world must be working in a very strange way, in which case it might be the case that his probability of (apparently) walking through my door is greater. Am I missing a simple argument?
You’re making a case that I should have less confidence in Obama’s existence as a result of his walking through the door? I can see where you’re going with it :-)
There are circumstances where X asserting A provides evidence against A (for not-A). Some speakers are less reliable than others and there is no necessary reason a speaker can’t be so unreliable that her claims provide zero evidence for or against what she asserts. Moreover, there is no reason a speaker can’t be anti-reliable. Perhaps she is a pathological liar. In this case her statements are inversely correlated with the truth and an assertion of A should be taken as evidence for not-A. As long as your math is right there is no reason for this to violate conservation of evidence.
Saying that X asserting A provides very weak evidence for A should not be confused with saying Y asserting B provides evidence for not-B. One claim is about magnitude while the other is about sign. In most situations, the latter commits one to violating conservation of evidence, but the former does not.
No, if you learn first that X is being claimed, then you learn that many people claim it for stupid reasons, then after learning the second fact your confidence in X goes down, as in this example:
There’s no violation of confirmation of evidence: not learning today that a particular religious tribe believe in an Australian-Zulu connection increases my confidence in the proposition by a tiny amount, just as Barack Obama not walking through the door right now decreases my confidence in his existence.
He’s insanely unlikely to walk through my door, but if after all the evidence he manages to not actually exist, the world must be working in a very strange way, in which case it might be the case that his probability of (apparently) walking through my door is greater. Am I missing a simple argument?
You’re making a case that I should have less confidence in Obama’s existence as a result of his walking through the door? I can see where you’re going with it :-)
There are circumstances where X asserting A provides evidence against A (for not-A). Some speakers are less reliable than others and there is no necessary reason a speaker can’t be so unreliable that her claims provide zero evidence for or against what she asserts. Moreover, there is no reason a speaker can’t be anti-reliable. Perhaps she is a pathological liar. In this case her statements are inversely correlated with the truth and an assertion of A should be taken as evidence for not-A. As long as your math is right there is no reason for this to violate conservation of evidence.