I've become interested in something called defeasible reasoning of late. I rather like the idea because it lets us argue from the perspective that one might be wrong. I can't get any moral authority from golden salamanders, so I'm interested in defeasible obligations, which give rise to defeasible inferences about what we are, all things considered, obliged to do. Thus I think we should act as though mankind is screwing up big-time and get more control of global warming, even if the evidence eventually turns out to have been misinterpreted. The ideas are not new. David Ross, in 1930, discussed the phenomena of prima facie obligations. The existence of a prima facie obligation gives one good, but defeasible grounds, for believing that one ought to fulfill that obligation. When formal deontic logic was developed by Chisholm and others in the 1960s, the use of classical logic gave rise to certain paradoxes, such as Chisholm's paradox of contrary-to-duty imperatives. These paradoxes can be resolved by recognizing that the inference from imperative to actual duty is a defeasible one. Prediction always involves an element of defeasibilty. If one predicts what will, or what would, under some hypotheis, happen, one must presume that there are no unknown factors that might interfere with those factors and conditions that are known. Any prediction can be upset by such unanticipated interventions. Prediction thus proceeds from the assumption that the situation as modeled constitutes a closed world: that nothing outside that situation could intrude in time to upset one's predictions. In addition, we seem to presume that any factor that is not known to be causally relevant is in fact causally irrelevant, since we are constantly encountering new factors and novel combinations of factors, and it is impossible to verify their causal irrelevance in advance. This closed-world assumption is one of the principal motivations for McCarthy's logic of circumscription (McCarthy 1982; McCarthy 1986).
Now this may be a bit clumsy, but I would hope all could see (say) that Chris and I could agree on what we ought to try to do about "global warming" based on a shared agreement that are arguments are defeasible (and possibly bullshit ridden). This is an altogether different stance in argument than points scoring, ad hominem and the rest. One might have to be careful in language when religious figures with surgical instruments are around, but circumscription allows the possibility that one's opponents may be right and takes into account what we don't currently know and that our opinions change in the flow of time forward.. I know I do not have a second sister, due to the absence of one - but would be convinced to change my mind should one appear. I know there is no 10.55 a.m. train into town, as none is listed. I have never knowingly sensed dark matter and have worked without knowing about it. My work might well take a different tack if the LHC finds the stuff. The point, I guess, is that we don't know much about the nature of the argument we so readily enter into, and how restricted it often is. I believe we could have much deeper, multi-voiced arguments about what we should do and would find one very loud, censoring tone preventing us taking circumspect action - our primitive and brutal notion of what an economy is. I doubt anyone here would want to read these papers, but some might be interested to note the area they come from. McCarthy, John M. and Patrick J. Hayes, 1969, “Some Philosophical Problems from the Standpoint of Artificial Intelligence”, in Machine Intelligence 4, B. Meltzer and D. Mitchie (eds.), Edinburgh: Edinburgh University Press. –––, 1977, “Epistemological Problems of Artificial Intelligence”, in Proceedings of the 5th International Joint Conference on Artificial Intelligence, Pittsburgh: Computer Science Department, Carnegie-Mellon University. –––, 1982, “Circumscription — A Form of Non-Monotonic Reasoning”, Artificial Intelligence, 13: 27-39, 171-177. –––, 1986, “Application of Circumscription to Formalizing Common-Sense Knowledge”, Artificial Intelligence, 28: 89-111. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups ""Minds Eye"" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/Minds-Eye?hl=en -~----------~----~----~----~------~----~------~--~---
