Venho acompanhando, Desidério, o Horty desde *Agency and Deontic Logic*. Esse novo livro parece ter uma grande amplitude (parece-me bastante ousado). Já saiu alguma resenha de nota?
Para quem não sabe, ele tem a política de, como o Makinson e vários outros, disponibilizar quase tudo o que escreveu, dentro do possível, em sua página pessoal: http://www.umiacs.umd.edu/~horty/publications.html Espero que a moda continue pegando! Abraços On 5 October 2012 10:36, Desidério Murcho <[email protected]>wrote: > Reasons as Defaults // Reviews // Notre Dame Philosophical Reviews // > University of Notre Dame > > http://ndpr.nd.edu/news/33798-reasons-as-defaults/?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+PhilosophicalReviews%2FNews+%28Notre+Dame+Philosophical+Reviews%29 > ------------------------------ > > This book combines foundational issues in moral and practical reasoning > with ideas in logic that may still be so new they are unfamiliar to many > philosophers. > > The text is sufficiently clear and self-contained to serve as an > introduction to nonmonotonic logic (or to one approach to it) for readers > with a general background in logic, but it is mainly concerned with how to > use the logical theory to inform philosophy. The logic itself can be stated > fairly simply by postponing complications and technical issues that lurk in > the background. Horty seeks to do this by moving most of these to the final > chapters and to appendices. > > Nonmonotonic logic seeks to deal with premises or axioms that are > defeasible or can have exceptions. Logics of this sort have mainly been > developed by computer scientists, but this does not affect their > philosophical interest or importance. Before so many logicians migrated to > computer science, theories of this sort would have been developed by > logically minded philosophers, and nonmonotonic logics address central > issues in philosophical logic and commonsense reasoning. Horty is one of > the few philosophers who participated in the development of these logics. > > The main purpose of the book is to trace the origins of reasons > (theoretical as well as practical), and to account for how they give rise > to conclusions. This, you might think, is the central task of logic, and > ought to have been solved in the distant past. But in a nonmonotonic > context it’s possible to do far more justice to realistic specimens of > reasoning, and to make closer contact with substantive philosophical > issues. Nonmonotonic logics are relatively new, and shed light on how > conflicting and exception-prone bodies of reasons can support conclusions. > > Horty begins by explaining “default logic”. This version of nonmonotonic > logic, due to Raymond Reiter, extends an ordinary first-order theory with a > set of “default rules”. An “extension” of such a theory is a set of > conclusions that consistently maximizes the list of default rules, without > bringing in any conclusions that aren’t supported by default rules and > logic. > > Defaults can conflict: for instance, authorities can provide contradictory > information, or issue contradictory commands. Reiter’s simple example of > such a conflict, known as the “Nixon Diamond,” represents an important > source of complexity in nonmonotonic logic and receives much attention in > Horty’s book. In this example, it is known (and only known) that Nixon is a > Quaker and a Republican. One default says that if Nixon is a Quaker he’s a > pacifist, another that if he’s a Republican he’s not a pacifist. The > default theory corresponding to the Nixon Diamond has two extensions: one > concluding that Nixon is a pacifist, the other that he is not. > > Such conflicts render the logical theory of default logic problematic by > confounding the notion of logical consequence. Reiter’s logic abandons the > idea that logical consequence relates a theory to a unique set of > conclusions. Instead, it produces a family of alternative conclusion sets — > a set of extensions. (In some anomalous cases this set can even be empty.) > There are ways to associate a unique set of consequences with a default > theory. A credulous theorist can (perhaps arbitrarily) choose one of these > extensions. A skeptical theorist can try to find what is common to these > extensions, perhaps by taking the intersection of their conclusions. Horty > returns to this issue often, exploring its increasingly complex > ramifications. > > The outcome of the first chapter is a (provisional) definition of the set > of extensions of an ordered default theory, in which the default rules are > (partially) ranked according to priority. If, for instance, we were to say > that the default “If Nixon is a Quaker he is a pacifist” has priority over > the default “If Nixon is a Republican he’s not a pacifist,” the theory > would then have only one extension, corresponding to the conclusion that > he’s a pacifist. > > Here, the weaker default is overridden. This definition determines the > underlying logic that Horty uses for the remainder of the book. > > In Chapter 2 the book moves from logic to philosophy, motivating and > elaborating a close connection between defaults and reasons. Think of a > scenario as the set of defaults that are used to build an extension of a > default theory. In creating and opting for a scenario (and hence, choosing > an extension or set of conclusions), a set of premises (which either belong > to the original theory or are concluded as part of the extension) will > combine with defaults to form conclusions. Horty wants to identify these > premises (relative to default theory and one of its scenarios) as the > reasons for the corresponding conclusions. Reasons are the premises of used > defaults. With the help of examples, Horty supports and develops this > thought, comparing it to similar ideas in the literature. This provides not > only an account or analysis of reasons, but, in combination with the theory > of logical consequence for defaults, brings into play a theory of how > reasons are selected from a competing set of considerations and of how > conclusions are drawn from them. > > Turning to deontic logic, Chapter 3 is concerned with the derivation of > oughts from reasons. Horty exhibits two ways to do this, which correspond > roughly to the credulous and skeptical approaches to default reasoning. The > first approach traces an ought with content P to the existence of an > extension supporting P, and so allows moral conflicts, i.e., cases in which > a proposition and its negation are both obligatory. The second approach > only admits oughts with content P when P is supported by all extensions, > and so produces a body of oughts that is free of moral conflicts. > > This is a topic that has received much attention in the philosophical > literature. In the course of developing his own account, Horty discusses > views of Roderick Chisholm, Gilbert Harman, Mark Schroeder, Earl Conee, > Phillipa Foot, Alan Donagan, David Brink, and others. Unlike these other > views, Horty’s own account is grounded in a logical theory of the > underlying reasoning. This is what was provided by the first chapter, which > in turn relies on thirty years of work in nonmonotonic logic. It is > instructive to see the difference that this makes in the quality of the > philosophical discussion, raising it to an entirely new level of clarity. > > The discussion of Brink’s work (pp. 77-80) illustrates this point well. > Horty shows that Brink’s account fails to produce the desired conclusions > in certain cases. It would be nearly impossible, I think, to have seen this > without being able to compare the formal model provided by Horty’s theory, > and the corresponding model that Horty constructs of Brink’s view. The > differences between the two theories, and the example that exposes the > problem in Brink’s account, would emerge from the failure of an attempt to > prove the equivalence of the two theories. Alternatively the task of > developing a formal theory like Horty’s and motivating it properly would > involve testing the theory with a suite of counterexamples, which would > include the ones that are problematic for Brink’s approach. In either case, > without the formalization process it would be difficult in areas as complex > as these to criticize the theories in the literature with much confidence. > The technical work informs and improves the quality of the philosophy. > > The advantages of an underlying logical theory can also be seen in the > discussion of agglomeration (pp. 89-92) and in the criticisms of Foot’s > views (pp. 101-102). > > The philosophical literature on the closely related topic of moral conflict > is also extensive. Horty’s careful discussion of this issue in Chapter 4 > shows convincingly the failure of arguments against the possibility of such > conflicts even in all-things considered oughts. Both the credulous option > (which admits moral conflicts) and the skeptical view (which does not) are > viable. This discussion sheds light on the philosophical issue, but if the > ideas presented in this book are to be extended to deal not just with > oughts but also with their role in the reasoning of a practical agent, it > may not eliminate closely related problems. (More about this in the > conclusion of this review.) > > The book now turns to what Horty calls “elaborations” of the basic theory. > These include a formal theory that allows priority relations between > defaults to be inferred and an examination of Jonathan Dancy’s > particularist views concerning reasons. Horty argues for a more moderate > approach than Dancy’s. The discussion exposes unexpected complexity in the > issues, and shows remarkable clarity in dealing with this complexity. > Again, the formal infrastructure is at work here. > > The remainder of the book (except for the appendices, which contain > technical material) has to do with complications and problems in the > underlying theory that were postponed until this point. Again, logical and > philosophical methods are harnessed together and put to work in a way that > illuminates both areas. A point that I find particularly interesting is the > treatment of skepticism. Just about any philosopher is liable to assume > that it’s clear what skepticism is, and will proceed immediately to deploy > (and usually refute) skeptical arguments. But in fact, the phenomenon of > “reinstatement” makes the notion of skepticism problematic. Suppose that as > reasoning creatures in an uncertain world, we’re forced to rely on > defaults. > > Skepticism, you’d think, would amount to a refusal to use defaults below > some confidence threshold. The problem is that such a refusal may actually > enable certain conclusions that would not be forthcoming from a less > “skeptical” standpoint. Paradoxically, a skeptic may be forced to believe > some things that a nonskeptic might reject. > > Before concluding, I want to situate the defaults, reasons and oughts on > which Horty’s book concentrates in the wider context of a reasoning agent. > To have moral and epistemic reasons, an agent will need to obtain defaults. > To use these reasons in acting, the agent will need to use them to form > goals, plan, and adopt intentions. > > First, consider the acquisition of defaults. In an explicit body of > regulations, these might be drafted in a legislative process. For an > individual, they will have to be learned. But how does this happen? Take > the case of epistemic defaults, factual norms about the way things should > be, and suppose they are learned as schemata, of the form “If P(x) then > Q(x)”. > > We have a good model of how probabilities are learned, but defaults are not > probabilities, even very high probabilities. A model of how defaults are > learned should tell us something about how bodies of evidence would support > a default scheme, and how they might lead us to reject an entertained > default scheme. But what is the difference between evidence that > disconfirms such a scheme, and evidence that is simply an exception? I’m > not sure that anyone has a good answer to this question, or even the > beginnings of a good theory of how defaults would be acquired by a rational > agent. > > Second, look in the other direction: how would default-derived norms figure > in practical deliberation? That is, how would they enter into goal > selection, planning, and intention formation? Goals aren’t the same as > oughts; for one thing, they involve desires, as well as norms. > > In some ways, desires are like defaults: standing desires can have > exceptions, and desires can conflict. But they would have to interact with > epistemic and normative defaults (because goals must be feasible and > permissible). I’m sure this interaction is complex because it involves very > different sorts of preferences between defaults, and I don’t think it’s > very well understood. Likewise, the formation of subgoals in planning has > to be informed by desires and epistemic and normative defaults, and will > also involve complex temporal reasoning. > > Perhaps the planning process would produce alternative coherent plans of > action, in much the same way that systems of defaults produce alternative > extensions. But then there would have to be room for rational (or at least, > reasoned) choice between these “practical extensions.” On the one hand, > some of these potential intentions would be preferable to others, and on > the other hand, intentions need to be specific and it would not do to > simply take what is common to all the alternative plans. (For one thing, > this is not likely to even be a coherent plan.) Here, it seems, neither > Horty’s skeptical nor his credulous alternative is appropriate. > > So, in both directions, further complexities are lurking if we wish to > extend Horty’s ideas. But the beauty of this book is that while at the same > time it opens unexpected and challenging complexity in familiar problems, > it provides tools to master this complexity with a sense that an outcome of > permanent value has been accomplished. In doing so, it takes the philosophy > of normative reasoning to a new level, and, I think, provides some hope > that this sort of clarity can be preserved even as the scope of the theory > is widened. > ------------------------------ > > (via Instapaper <http://www.instapaper.com/>) > _______________________________________________ > Logica-l mailing list > [email protected] > http://www.dimap.ufrn.br/cgi-bin/mailman/listinfo/logica-l > _______________________________________________ Logica-l mailing list [email protected] http://www.dimap.ufrn.br/cgi-bin/mailman/listinfo/logica-l
