We propose a new relevance sensitive model for representing and revising belief structures, which relies on a notion of partial language splitting and tolerates some amount of inconsistency while retaining classical logic. The model preserves an agent's ability to answer queries in a coherent way using Belnap's four-valued logic. Axioms analogous to the AGM axioms hold for this new model. The distinction between implicit and explicit beliefs is represented and psychologically plausible, computationally tractable procedures for query answering and belief..

The axiom of recovery, while capturing a central intuition regarding belief change, has been the source of much controversy. We argue briefly against putative counterexamples to the axiom—while agreeing that some of their insight deserves to be preserved—and present additional recovery-like axioms in a framework that uses epistemic states, which encode preferences, as the object of revisions. This makes iterated revision possible and renders explicit the connection between iterated belief change and the axiom of recovery. We provide a representation theorem (...) that connects the semantic conditions we impose on iterated revision and our additional syntactical properties. We show interesting similarities between our framework and that of Darwiche–Pearl (Artificial Intelligence 89:1–29 1997). In particular, we show that intuitions underlying the controversial (C2) postulate are captured by the recovery axiom and our recovery-like postulates (the latter can be seen as weakenings of (C2)). We present postulates for contraction, in the same spirit as the Darwiche–Pearl postulates for revision, and provide a theorem that connects our syntactic postulates with a set of semantic conditions. Lastly, we show a connection between the contraction postulates and a generalisation of the recovery axiom. (shrink)

Possible-world semantics are provided for Parikh’s relevance-sensitive model for belief revision. Having Grove’s system-of-spheres construction as a base, we consider additional constraints on measuring distance between possible worlds, and we prove that, in the presence of the AGM postulates, these constraints characterize precisely Parikh’s axiom (P). These additional constraints essentially generalize a criterion of similarity that predates axiom (P) and was originally introduced in the context of Reasoning about Action. A by-product of our study is the identification of two possible (...) readings of Parikh’s axiom (P), which we call the strong and the weak versions of the axiom. An interesting feature of the strong version is that, unlike classical AGM belief revision, it makes associations between the revision policies of different theories. (shrink)

Traditional accounts of belief change have been criticized for placing undue emphasis on the new belief provided as input. A recent proposal to address such issues is a framework for non-prioritized belief change based on default theories (Ghose and Goebel, 1998). A novel feature of this approach is the introduction of disbeliefs alongside beliefs which allows for a view of belief contraction as independently useful, instead of just being seen as an intermediate step in the process of belief revision. This (...) approach is, however, restrictive in assuming a linear ordering of reliability on the received inputs. In this paper, we replace the linear ordering with a preference ranking on inputs from which a total preorder on inputs can be induced. This extension brings along with it the problem of dealing with inputs of equal rank. We provide a semantic solution to this problem which contains, as a special case, AGM belief change on closed theories. (shrink)

Routledge (New Media and Cyberculture Series), July 2007.

We present a method for relevance sensitive non-monotonic inference from belief sequences which incorporates insights pertaining to prioritized inference and relevance sensitive, inconsistency tolerant belief revision. Our model uses a finite, logically open sequence of propositional formulas as a representation for beliefs and defines a notion of inference from maxiconsistent subsets of formulas guided by two orderings: a temporal sequencing and an ordering based on relevance relations between the putative conclusion and formulas in the sequence. The relevance relations are ternary (...) (using context as a parameter) as opposed to standard binary axiomatizations. The inference operation thus defined easily handles iterated revision by maintaining a revision history, blocks the derivation of inconsistent answers from a possibly inconsistent sequence and maintains the distinction between explicit and implicit beliefs. In doing so, it provides a finitely presented formalism and a plausible model of reasoning for automated agents. (shrink)

We provide a formal study of belief retraction operators that do not necessarily satisfy the postulate. Our intuition is that a rational description of belief change must do justice to cases in which dropping a belief can lead to the inclusion, or ‘liberation’, of others in an agent's corpus. We provide two models of liberation via retraction operators: ρ-liberation and linear liberation. We show that the class of ρ-liberation operators is included in the class of linear ones and provide axiomatic (...) characterisations for each class. We show how any retraction operator can be ‘converted’ into either a withdrawal operator ) or a revision operator via the Harper Identity and the Levi Identity respectively. (shrink)

Thinking about how the law might decide whether to extend legal personhood to artificial agents provides a valuable testbed for philosophical theories of mind. Further, philosophical and legal theorising about personhood for artificial agents can be mutually informing. We investigate two case studies, drawing on legal discussions of the status of artificial agents. The first looks at the doctrinal difficulties presented by the contracts entered into by artificial agents. We conclude that it is not necessary or desirable to postulate artificial (...) agents as legal persons in order to account for such contracts. The second looks at the potential for according sophisticated artificial agents with legal personality with attendant constitutional protections similar to those accorded to humans. We investigate the validity of attributes that have been suggested as pointers of personhood, and conclude that they will take their place within a broader matrix of pragmatic, philosophical and extra-legal concepts. (shrink)

The standard theory for belief revision provides an elegant and powerful framework for reasoning about how a rational agent should change its beliefs when confronted with new information. However, the agents considered are extremely idealized. Some recent models attempt to tackle the problem of plausible belief revision by adding structure to the belief bases and using nonstandard inference operations. One of the key ideas is that not all of an agent's beliefs are relevant for an operation of belief change.In this (...) paper we incorporate the insights pertaining to local change and relevance sensitivity with the use of approximate inference relations. These approximate inference relations offer us partial solutions at any stage of the revision process. The quality of the approximations improves as we allow for more and more resources to be used. We are provided with upper and lower bounds to what would be obtained with the use of classical inference. (shrink)

The introduction of explicit notions of rejection, or disbelief, into logics for knowledge representation can be justified in a number of ways. Motivations range from the need for versions of negation weaker than classical negation, to the explicit recording of classic belief contraction operations in the area of belief change, and the additional levels of expressivity obtained from an extended version of belief change which includes disbelief contraction. In this paper we present four logics of disbelief which address some or (...) all of these intuitions. Soundness and completeness results are supplied and the logics are compared with respect to applicability and utility. (shrink)

Claims about the potential of free software to reform the production and distribution of software are routinely countered by skepticism that the free software community fails to engage the pragmatic and economic ‘realities’ of a software industry. We argue to the contrary that contemporary business and economic trends definitively demonstrate the financial viability of an economy based on free software. But the argument for free software derives its true normative weight from social justice considerations: the evaluation of the basis for (...) a software economy should be guided by consideration of the social and cultural states which are the ultimate goals of any economic arrangement. That is, the software economy should be evaluated in light of its ability to provide justice. We conclude with a discussion of possible avenues for reform. (shrink)

in Proceedings of the International Joint Conference on Artificial Intelligence, 2007.

This thesis proposes and presents two new models for belief representation and belief revision. The first model is the B-structures model which relies on a notion of partial language splitting and tolerates some amount of inconsistency while retaining classical logic. The model preserves an agent's ability to answer queries in a coherent way using Belnap's four-valued logic. Axioms analogous to the AGM axioms hold for this new model. The distinction between implicit and explicit beliefs is represented and psychologically plausible, computationally (...) tractable procedures for query answering and belief base revision are obtained. ;The second model presents a method for relevance sensitive non-monotonic inference from belief sequences which incorporates insights pertaining to prioritized inference and relevance sensitive, inconsistency tolerant belief revision. Our model uses a finite, logically open sequence of propositional formulas as a representation for beliefs and defines a notion of inference from maxiconsistent subsets of formulas guided by two orderings: a temporal sequencing and an ordering based on relevance relations between the conclusion and formulas in the sequence. The relevance relations are ternary as opposed to standard binary axiomatizations. The inference operation thus defined easily handles iterated revision by maintaining a revision history, blocks the derivation of inconsistent answers from a possibly inconsistent sequence and maintains the distinction between explicit and implicit beliefs. In doing so, it provides a finitely representable formalism and a plausible model of reasoning for automated agents. (shrink)

Through inspirational wisdom, compelling storytelling, and practical advice, this book will help you discover your life's purpose.

The “free” in “free software” refers to a cluster of four specific freedoms identified by the Free Software Definition. The first freedom, termed “Freedom Zero,” intends to protect the right of the user to deploy software in whatever fashion, towards whatever end, he or she sees fit. But software may be used to achieve ethically questionable ends. This highlights a tension in the provision of software freedoms: while the definition explicitly forbids direct restrictions on users’ freedoms, it does not address (...) other means by which software may indirectly restrict freedoms. In particular, ethically-inflected debate has featured prominently in the discussion of restrictions on digital rights management and privacy-violating code in version 3 of the GPL (GPLv3). The discussion of this proposed language revealed the spectrum of ethical positions and valuations held by members of the free software community. In our analysis, we will provide arguments for upholding Freedom Zero; we embed the problem of possible uses of software in the broader context of the uses of scientific knowledge, and go on to argue that the provision of Freedom Zero mitigates against too great a moral burden—of anticipating possible uses of software—being placed on the programmer and that, most importantly, it facilitates deliberative discourse in the free software community. (shrink)

Free and open source software is taking an increasingly significant role in our software infrastructure. Yet many questions still exist about whether a software economy based on FOSS would be viable. We argue that contemporary trends definitively demonstrate this viability. Claiming that an economy must be evaluated as much by the ends it brings about as by its size or vigor, we draw on widely accepted notions of redistributive justice to show the ethical superiority of a software economy based on (...) FOSS. (shrink)

To walk or not to walk: Should a batsman acknowledge his own dismissal by leaving the wicket without even waiting for the umpire's decision? David Coady and Samir Chopra examine this flashpoint ethical debate in cricket.

We present a framework that provides a logic for science by generalizing the notion of logical (Tarskian) consequence. This framework will introduce hierarchies of logical consequences, the first level of each of which is identified with deduction. We argue for identification of the second level of the hierarchies with inductive inference. The notion of induction presented here has some resonance with Popper's notion of scientific discovery by refutation. Our framework rests on the assumption of a restricted class of structures in (...) contrast to the permissibility of classical first-order logic. We make a distinction between deductive and inductive inference via the notions of compactness and weak compactness. Connections with the arithmetical hierarchy and formal learning theory are explored. For the latter, we argue against the identification of inductive inference with the notion of learnable in the limit. Several results highlighting desirable properties of these hierarchies of generalized logical consequence are also presented. (shrink)

We present a model for first-order belief revision that is characterized by an underlying relevance-like relation and a background proof system. The model is extremely general in order to allow for a wide variety in these characterizing parameters. It allows some weakenings of beliefs which were initially implicit to become explicit and survive the revision process. The effects of revision are localized to the part of the theory that is influenced by the the new information. Iterated revision in this model (...) is handled trivially since the revision operator is constructive by definition. The usage of deductively limited proof systems permits an inconsistency tolerant model. The notion of a part of a theory capable of being influenced by new information (designed to accomodate the specific character of first-order languages) is shown to satisfy some intuitive and desirable properties. We show that for particular parametrizations, standard revision schemes can be embedded into our paradigm. (shrink)

Our freedoms in cyberspace are those granted by code and the protocols it implements. When man and machine interact, co-exist, and intermingle, cyberspace comes to interpenetrate the real world fully. In this cyborg world, software retains its regulatory role, becoming a language of interaction with our extended cyborg selves. The mediation of our extended selves by closed software threatens individual autonomy. We define a notion of freedom for software that does justice to our conception of it as language, sketching the (...) outlines of a social and political philosophy for a cyborg world. In a cyberspace underwritten by free software, political structures become contingent and flexible: the polity can choose to change the extent and character of its participation. The rejection of opaque power is an old anarchist ideal: free software, by making power transparent, carries the potential to place substantive restrictions on the regulatory power of cyborg government. (shrink)

Dept of Business Administration Dept of Computer and Knowledge Systems Group University of Patras Information Science School of Computer Science 265 00 Patras, Greece Brooklyn College of the and Engineering [email protected] City University of New York University of New South Wales Brooklyn, NY 11210, USA Sydney, NSW 2052, Australia [email protected] [email protected]

Software is much more than sequences of instructions for a computing machine: it can be an enabler (or disabler) of political imperatives and policies. Hence, it is subject to the same assessment in a normative dimension as other political and social phenomena. The core distinction between free software and its proprietary counterpart is that free software makes available to its user the knowledge and innovation contributed by the creator(s) of the software, in the form of the created source code. From (...) an ethical perspective, one of the most pressing questions raised by this form of collaboration is the question of the rights, and the restrictions on them, that are passed on to users and collaborators by the creators of programs. That is, what freedoms do software users deserve, and how can they best be protected? In this study we analyze free software licensing schemes in order to determine which most effectively protects such freedoms. We conclude that so-called copyleft licensing schemes are the morally superior alternative. (shrink)