On Fri, Oct 10, 2008 at 8:29 PM, Pei Wang <[EMAIL PROTECTED]> wrote: > On Fri, Oct 10, 2008 at 8:03 PM, Ben Goertzel <[EMAIL PROTECTED]> wrote: > > > > Yah, according to Bayes rule if one assumes P(bird) = P(swimmer) this > would > > be the case... > > > > (Of course, this kind of example is cognitively misleading, because if > the > > only knowledge > > the system has is "Swallows are birds" and "Swallows are NOT swimmers" > then > > it doesn't > > really know that the terms involved are "swallows", "birds", "swimmers" > etc. > > ... then in > > that case they're just almost-meaningless tokens to the system, right?) > > Well, it depends on the semantics. According to model-theoretic > semantics, if a term has no reference, it has no meaning. According to > experience-grounded semantics, every term in experience have meaning > --- by the role it plays.
That's why I said "almost-meaningless" ... if those are the only relationships known to the system, then the terms in those relationships play almost no roles, hence have almost no meanings... > > Further questions: > > (1) Don't you intuitively feel that the evidence provided by > non-swimming birds says more about "Birds are swimmers" than > "Swimmers are birds"? Yes, but only because I know intuitively that swimmers are more common in my everyday world than birds. That illustrates why it's confusing to use commonsense terms in artificially isolated inference examples. (I take that expository strategy in the PLN book too, but it can be misleading.) > > > (2) If your answer for (1) is "yes", then think about "Adults are > alcohol-drinkers" and "Alcohol-drinkers are adults" --- do they have > the same set of counter examples, intuitively speaking? Again, our intuitions for this are colored by the knowledge that there are more adults than alcohol-drinkers. Consider high school, which has 4 years: freshman, sophomore, junior, senior. Then think about "Juniors & seniors are women" and "women are juniors & seniors" It seems quite intuitive to me that, in this case, the same pieces of evidence support the truth values of these two hypotheses. This is because the term probabilities of "juniors and seniors" and "women" are intuitively known to be about equal. (3) According to your previous explanation, will PLN also take a red > apple as negative evidence for "Birds are swimmers" and "Swimmers are > birds", because it reduces the "candidate pool" by one? Of course, the > probability adjustment may be very small, but qualitatively, isn't it > the same as a non-swimming bird? If not, then what the system will do > about it? Yes, in principle, PLN will behave in "Hempel's confirmation paradox" in a similar way to other Bayesian systems. I do find this counterintuitive, personally, and I spent a while trying to work around it ... but finally I decided that my intuition is the faulty thing. As you note, it's a very small probability adjustment in these cases, so it's not surprising if human intuition is not tuned to make such small probability adjustments in a correct or useful way... -- Ben ------------------------------------------- agi Archives: https://www.listbox.com/member/archive/303/=now RSS Feed: https://www.listbox.com/member/archive/rss/303/ Modify Your Subscription: https://www.listbox.com/member/?member_id=8660244&id_secret=114414975-3c8e69 Powered by Listbox: http://www.listbox.com
