I’m sure something similar could be a valid argument in favour of treating argument from authority as useful evidence, but I’m not finding it straightforward to check this argument above to see if it works.
‘available evidence’ in the last (THEN) line includes ‘Bob says Gloops are plink’ but ‘evidence available’ in the first three lines does not, right? Can the ‘all evidence available’ and ‘all other available evidence’ in the first three lines be taken to include all prior evidence known before finding out ‘Bob says Gloops are plink’? If so, the first three premises are contradictory—Bob says Gloops are plink 0.7 of the time, and almost all of that time he is correct, so p(Gloops are plink) > 0.4. If not, I need some further clarification of what probabilities are conditional on what evidence.
If so, the first three premises are contradictory—Bob says Gloops are plink 0.7 of the time, and almost all of that time he is correct, so p(Gloops are plink) > 0.4.
Thankyou and well spotted. Those completely arbitrary magic numbers don’t stand up to a second glance. In particular 0.7 is just silly. If you already know what the expert is going to say you barely need the expert to say it and so cannot be in a state of knowledge such that p(B) is so low. I’d better change them.
I’m sure something similar could be a valid argument in favour of treating argument from authority as useful evidence, but I’m not finding it straightforward to check this argument above to see if it works.
‘available evidence’ in the last (THEN) line includes ‘Bob says Gloops are plink’ but ‘evidence available’ in the first three lines does not, right? Can the ‘all evidence available’ and ‘all other available evidence’ in the first three lines be taken to include all prior evidence known before finding out ‘Bob says Gloops are plink’? If so, the first three premises are contradictory—Bob says Gloops are plink 0.7 of the time, and almost all of that time he is correct, so p(Gloops are plink) > 0.4. If not, I need some further clarification of what probabilities are conditional on what evidence.
Thankyou and well spotted. Those completely arbitrary magic numbers don’t stand up to a second glance. In particular 0.7 is just silly. If you already know what the expert is going to say you barely need the expert to say it and so cannot be in a state of knowledge such that p(B) is so low. I’d better change them.
That didn’t solve the main problem, I think I found what it was. I’ll reply to the other post.