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vc wrote:
> Keith H Duggar wrote: > [ A lot of irrelevant chaff skipped] >
> > OK, good, so you continue to claim that the probability of P(A and B) > is determined solely by P(A) and P(B) just as you did before: > > "When you apply the connectives to a probability-valued > statements you get probability-valued statements whose > probability depends only on the constituent probabilities. > "
I don't see how you draw the inference you draw. Clearly, P(B|A) and P(A|B) are constituent probabilities as well.
Show how to derive P(A and B) given P(A) and P(B). If you > can show that, you can claim that "probability depends only on the > constituent probabilities". Are you unable to do that ?
P(A and B) = P(B|A)P(A)
P(A and B) = P(A|B)P(B)
To derive P(A and B) one must know either P(B|A) or P(A|B) just as one must know the angle between two sides to use the cosine law. You fail to demonstrate anything useful or meaningful by your challenge.
>>>What kind of sentences do you have in mind whose
>>>probability is one?
>>
>>>Please provide a meaningful example.
>>
>>What are you talking about? It's not hard. It's trivial and
>>irrelevant! For proving probability theorems or that
>>probability is a generalization of logic it does not matter
>>what A, B, C etc stand for! "My first name is Keith" "My
>>last name is Duggar" "My first name is Keith or my last name
>>is Duggar". Does that satisfy you? I hope so because it is
>>TOTALLY irrelevant (and somewhat VI honestly).
>>
>>[disjunction nagging]
>>
>>
>>>2. In some case, namely when probabilities are 0 and 1,
>>>the probabilistic statements 'reduce' to logical
>>>statements. I asked to provide two or more statements
>>>whose probability would be one and show what the
>>>probability of the disjunction of such statements might
>>>be. There has been no answer. Are you unable to answer the
>>>question ?
> > What you've provided is not a meaningful example, but just two > mutually irrelevant true propositions (similarly to introducing > irrelevancy with penguins and the leaking roof in the Jaynes book). To > provide a meaningful example of reducing probabilities, take for > example two relevant statements A='It will rain today' and 'The roof > will leak' (see the same book), assign priors and show how P(A and B) > can be equal to one. > > Also, your 'basic proof' is quite meaningless (as I pointed out in > another message): > >
[light bulb goes on]
Keith already specified the argument applies to a limit.
>>P(A) = 1
>>P(A or B) = P(~(~A and ~B))
>>P(A or B) = 1 - P(~A and ~B)
>>P(A or B) = 1 - P(~B|~A)P(~A)
> > > Since P(~A) equals zero, the above statement does not make sense.
But Keith stated "in the limit of". Thus, one could read the first line of what he wrote as
lim P(A) as P(A) -> 1
which makes the other factor
lim P(~A) as P(~A) -> 0.
Thus, in the limit as P(A) approaches 1, P(A or B) = 1 - P(~B|~A)(1-P(A)) = 1
If he rewrote the proof using explicit limit notation, would you still object to his proof? Received on Sun Jun 11 2006 - 20:12:22 CDT