DanielLC comments on Evidence and counterexample to positive relevance - Less Wrong

-2 Post author: fsopho 25 May 2013 06:40PM

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Comment author: DanielLC 25 May 2013 07:01:13PM 2 points [-]

In the counterexample, e1 and e2 are each evidence of h on there own, but when the other is known, they are not.

(High Probability) e is evidence that h iff P(h|e) > k.

By this definition, if e and h are independent, but h has a prior probability higher than k, then e is evidence for h. For that matter, you could get something like P(h|e) = k+ε, P(h) = 1-ε. By this definition, e is evidence of h, even though e makes h dramatically less likely.

Also, this means that a confession is not evidence for a crime, because you need to know the language for it to mean anything.

Comment author: pragmatist 27 May 2013 09:54:57AM 1 point [-]

By this definition, if e and h are independent, but h has a prior probability higher than k, then e is evidence for h.

No, because in that case Achinstein's first condition won't be satisfied. If I'm reading the post right, both conditions need to be satisfied in order for e to count as evidence for h according to this definition.

Comment author: fsopho 27 May 2013 02:05:36PM 0 points [-]

Actually, Achinstein's claim is that the first one does not need to be satisfied - the probability of h does not need to be increased by e in order for e to be evidence that h. He gives up the first condition because of the counterexamples.

Comment author: pragmatist 27 May 2013 04:44:30PM *  0 points [-]

Well, duh. You're right, the post was pretty clear about this. I need to read more carefully. So does he believe that the second condition is both necessary and sufficient? That seems prone to a bunch of counterexamples also.

Comment author: fsopho 27 May 2013 06:25:45PM 0 points [-]

So, he claims that it is just a necessary condition - not a sufficient one. I didn't reach the point where he offers the further conditions that, together with high probability, are supposed to be sufficient for evidential support.

p.s: still, you earned a point for the comment =|