How do opinion diversity and belief polarisation affect epistemic group decision-making, particularly if decisions must be made without delay and on the basis of permissive evidence? In an agent-based model, we track the consistency of group opinions aggregated through sentence-wise majority voting. Simulations on the model reveal that high opinion diversity, but not polarisation, incurs a significant inconsistency risk. These results indicate that epistemic group decisions based on permissive evidence can be particularly difficult for diverse groups. The results also improve (...) our understanding of what can reasonably be expected of expert groups, and where expert advice might have limits. (shrink)

The problem of how to accommodate inconsistencies has attracted quite a number of researchers, in particular, in the area of database theory. The problem is also of concern in the study of belief change. For inconsistent beliefs are ubiquitous. However, comparatively little work has been devoted to discussing the problem in the literature of belief change. In this paper, I examine how adequate the AGM theory is as a logical framework for belief change involving inconsistencies. The technique is (...) to apply to Grove’s sphere system, a semantical representation of the AGM theory, logics that do not infer everything from contradictory premises, viz., paraconsistent logics. I use three paraconsistent logics and discuss three sphere systems that are based on them. I then examine the completeness of the postulates of the AGM theory with respect to the systems. At the end, I discuss some philosophical implications of the examination. (shrink)

The most pressing difficulty coherentism faces is, I believe, the problem of justified inconsistent beliefs. In a nutshell, there are cases in which our beliefs appear to be both fully rational and justified, and yet the contents of the beliefs are inconsistent, often knowingly so. This fact contradicts the seemingly obvious idea that a minimal requirement for coherence is logical consistency. Here, I present a solution to one version of this problem.

Suppose that I hold a ticket in a fair lottery and that I believe that my ticket will lose [L] on the basis of its extremely high probability of losing. What is the appropriate epistemic appraisal of me and my belief that L? Am I justified in believing that L? Do I know that L? While there is disagreement among epistemologists over whether or not I am justified in believing that L, there is widespread agreement that I do not know (...) that L. I defend the two-pronged view that I am justified in believing that my ticket will lose and that I know that it will lose. Along the way, I discuss four different but related versions of the lottery paradox—The Paradox for Rationality, The Paradox for Knowledge, The Paradox for Fallibilism, and The Paradox for Epistemic Closure—and offer a unified resolution of each of them. (shrink)

In this paper I investigate whether there are any cases in which it is rational for a person to hold inconsistent beliefs and, if there are, just what implications this might have for the theory of epistemic justification. A number of issues will crop up along the way – including the relation between justification and rationality, the nature of defeat, the possibility of epistemic dilemmas, the importance of positive epistemic duties, and the distinction between transitional and terminal attitudes.

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)

We present a model for studying communities of epistemically interacting agents who update their belief states by averaging the belief states of other agents in the community. The agents in our model have a rich belief state, involving multiple independent issues which are interrelated in such a way that they form a theory of the world. Our main goal is to calculate the probability for an agent to end up in an inconsistent belief state due to updating. To that (...) end, an analytical expression is given and evaluated numerically, both exactly and using statistical sampling. It is shown that, under the assumptions of our model, an agent always has a probability of less than 2% of ending up in an inconsistent belief state. Moreover, this probability can be made arbitrarily small by increasing the number of independent issues the agents have to judge or by increasing the group size. A real-world situation to which this model applies is a group of experts participating in a Delphi-study. (shrink)

Whether people possess free will has been a long-lasting philosophical debate. Recent attention in social psychology has been given to the behavioral consequences of believing in free will. Research has demonstrated that manipulating free will beliefs has implications for many social behaviors. For example, free will belief manipulations have been associated with cheating, aggressiveness, and prejudice. Despite this work, some of these findings have failed to replicate. Testing theoretical predictions, such as whether believing in free will influences behavior, depends (...) on theoretical, auxiliary, statistical, and inferential assumptions (TASI). In this paper we apply the TASI category of assumptions to the free will belief debate. In doing so we demonstrate why these assumptions should be considered when appraising the influence of free will belief manipulations on free will beliefs and behavior. To provide a nuanced view of free will beliefs, we believe researchers should pay careful attention to these critical assumptions. (shrink)

Inconsistency and contradiction are important concepts. Unfortunately, they are easily confused. A proposition or belief which is inconsistent is one which is self- contradictory and vice-versa. Moreover two propositions or beliefs which are contradictories are inconsistent with each other. Nonetheless it is a mistake to suppose that inconsistency is the same as contradiction.

We give a model for iterated belief change in multi-agent systems. The formal tool we use for this is a combination of modal and dynamic logic. Two core notions in our model are the expansion of the knowledge and beliefs of an agent, and the processing of new information. An expansion is defined as the change in the knowledge and beliefs of an agent when it decides to believe an incoming formula while holding on to its current propositional (...) beliefs. To prevent our agents from forming inconsistent beliefs they do not expand with every piece of information they receive. Instead, our agents remember their original beliefs and every piece of information they receive. After every receipt of information they decide which subset of the received information should be incorporated into their original beliefs. This procedure is called the processing of new information. We show that our model of belief update behaves in an intuitive way and that it is not sensitive to criticism on comparable models. (shrink)

Idealized scientific representations result from employing claims that we take to be false. It is not surprising, then, that idealizations are a prime example of allegedly inconsistent scientific representations. I argue that the claim that an idealization requires inconsistent beliefs is often incorrect and that it turns out that a more mathematical perspective allows us to understand how the idealization can be interpreted consistently. The main example discussed is the claim that models of ocean waves typically involve (...) the false assumption that the ocean is infinitely deep. While it is true that the variable associated with depth is often taken to infinity in the representation of ocean waves, I explain how this mathematical transformation of the original equations does not require the belief that the ocean being modeled is infinitely deep. More generally, as a mathematical representation is manipulated, some of its components are decoupled from their original physical interpretation. (shrink)

(I) It is commonly held that a person cannot wittingly hold false or inconsistent beliefs. Edgley has argued that this follows from the normative implications involved in the concept of belief and the concept of a proposition, as expressed in the analytic principle 'if p, then it is right to think that p\ (II) But the principle, when taken in its analytic sense, does not have the required implications; and taken in the sense in which it would have (...) those implications it is neither analytic nor true. (III) A person can not only hold a false belief wittingly, he can assert that he does. Examples are given to exhibit the legitimacy of the claim that such irrationality does not necessarily dissolve when recognized for what it is. (IV) The phenomenon of self-confessed irrationality involves the fusion of two general features of mental life. It comprises a mental state over whose existence one has no control, but which one can in some way detach oneself from and be critical of. (shrink)

William Simkulet has recently criticised Colgrove et al’s defence against what they have called inconsistency arguments—arguments that claim opponents of abortion (OAs) act in ways inconsistent with their underlying beliefs about human fetuses (eg, that human fetuses are persons at conception). Colgrove et al presented three objections to inconsistency arguments, which Simkulet argues are unconvincing. Further, he maintains that OAs who hold that the fetus is a person at conception fail to act on important issues such as the (...) plight of frozen embryos, poverty and spontaneous abortion. Thus, they are morally negligent. In response, we argue that Simkulet has targeted a very narrow group of OAs, and so his criticisms are inapplicable to most OAs. We then explain why his responses to each of Colgrove et al’s objections do not succeed, even for this restricted group. Finally, we note that Simkulet fails to provide evidence for his claims regarding OAs’ supposed failures to act, and we show that OAs veritably do invest resources into these important issues. We conclude that Colgrove et al’s reasons for rejecting inconsistency arguments (en masse) remain intact. (shrink)

Cicero often challenged Epicureanism on the grounds of inconsistency. Cicero personifies the charge through his character Torquatus, who defends Epicureanism in De finibus 1–2. Cicero highlights the discrepancies among Torquatus’ beliefs and between them and his behaviour. Torquatus holds that the senses incontestably verify the tenets of Epicureanism, and that logic is superfluous. Yet he is sensitive to the fact that Epicurus’ teachings are not intuitive and require a fair amount of logical argumentation in its defence. Therefore, he defends (...) his school against Cicero's criticisms. But by engaging in a defence of the system, Torquatus has already spoken against his commitment to the obviousness of Epicureanism and his disavowal of logic. (shrink)

Abortion opponents are sometimes accused of having inconsistent beliefs, actions, and/or priorities. If they were consistent, they would regard spontaneous abortions to be a greater moral tragedy,...

“Probably Peirce’s best-known works are the first two articles in a series of six that originally were collectively entitled Illustrations of the Logic of Science and published in Popular Science Monthly from November 1877 through August 1878. The first is entitled ‘The Fixation of Belief’ and the second is entitled ‘How to Make Our Ideas Clear.’ In the first of these papers Peirce defended, in a manner consistent with not accepting naive realism, the superiority of the scientific method over other (...) methods of overcoming doubt and ‘fixing belief.’” — Robert Burch, “Charles Sanders Peirce,” entry in the Stanford Encyclopedia of Philosophy (2021 revision) -/- “Pragmatist epistemologies often explore how we can carry out inquiries in a self-controlled and fruitful way. (Where much analytic epistemology centres around the concept of knowledge, considered as an idealised end-point of human thought, pragmatist epistemology centres around the concept of inquiry, considered as the process of knowledge-seeking and how we can improve it.) So pragmatists often provide rich accounts of the capacities or virtues that we must possess in order to inquire well, and the rules or guiding principles that we should adopt. A canonical account is Peirce’s classic early paper ‘The Fixation of Belief‘. Here Peirce states that inquiry is a struggle to replace doubt with “settled belief“, and that the only method of inquiry that can make sense of the fact that at least some of us are disturbed by inconsistent beliefs, and will subsequently reflect upon which methods of fixing belief are correct is the Method of Science, which draws on the Pragmatic Maxim described above. This contrasts with three other methods of fixing belief: i) refusing to consider evidence contrary to one’s favored beliefs (the Method of Tenacity), ii) accepting an institution’s dictates (the Method of Authority), iii) developing the most rationally coherent or elegant-seeming belief-set (the A Priori Method).“ — Catherine Legg, “Pragmatism,” entry in the Stanford Encyclopedia of Philosophy (2021 revision). (shrink)

The relationship between inconsistency and Lehrerian coherence is scrutinized. Like most coherence theorists of epistemic justification, Lehrer contends that consistency is necessary for coherence. Despite this contention, minimally inconsistent belief-sets prove coherent and rationally acceptable on Lehrer's account of coherence. Lehrer is left with the following dilemma: If consistency is necessary for coherence, then (i) he must revise his account of coherence accordingly and, more importantly, (ii) such coherence is nof necessary for justification, since intuitively we are justified in (...) accepting such minimally inconsistent belief-sets. If, on the other hand, minimally inconsistent acceptance systems can be coherent, then to prevent pairwise inconsistent statements form readily cohering with such systems, Lehrer must deny that rational acceptance is closed under deduction. (shrink)

In section I, I argue that the principal reason why inconsistency is a fault is that it involves having at least one false belief. In section 2, I argue that inconsistency need not be a serious epistemic fault. The argument in section 2 is based on the notion that what matters epistemically is always in the final analysis an item's effect on attaining the goal of truth. In section 3 I describe two cases in which it is best from an (...) epistemic point of view to knowingly retain inconsistent beliefs. In section 4 my goal is to put into perspective the charge that relativism ought to be rejected because it involves one in inconsistency. (shrink)

If a subject’s belief system is inconsistent, does it follow that the subject’s beliefs (all of them) are unjustified? It seems not. But, coherentist theories of justification (at least some of them) imply otherwise, and so, it seems, are open to counterexample. This is the “Problem of Justified Inconsistent Beliefs”. I examine two main versions of the Problem of Justified Inconsistent Beliefs, and argue that coherentists can give at least a promising line of response (...) to each of them. (shrink)

I present a possible worlds semantics for a hyperintensional belief revision operator, which reduces the logical idealization of cognitive agents affecting similar operators in doxastic and epistemic logics, as well as in standard AGM belief revision theory. (Revised) belief states are not closed under classical logical consequence; revising by inconsistent information does not perforce lead to trivialization; and revision can be subject to ‘framing effects’: logically or necessarily equivalent contents can lead to different revisions. Such results are obtained without (...) resorting to non-classical logics, or to non-normal or impossible worlds semantics. The framework combines, instead, a standard semantics for propositional S5 with a simple mereology of contents. (shrink)

Opponents of abortion are commonly said to be inconsistent in their beliefs or actions, and to fail in their obligations to prevent the deaths of embryos and fetuses from causes other than induced...

This study examines the problem of belief revision, defined as deciding which of several initially accepted sentences to disbelieve, when new information presents a logical inconsistency with the initial set. In the first three experiments, the initial sentence set included a conditional sentence, a non‐conditional (ground) sentence, and an inferred conclusion drawn from the first two. The new information contradicted the inferred conclusion. Results indicated that conditional sentences were more readily abandoned than ground sentences, even when either choice would lead (...) to a consistent belief state, and that this preference was more pronounced when problems used natural language cover stories rather than symbols. The pattern of belief revision choices differed depending on whether the contradicted conclusion from the initial belief set had been a modus ponens or modus tollens inference. Two additional experiments examined alternative model‐theoretic definitions of minimal change to a belief state, using problems that contained multiple models of the initial belief state and of the new information that provided the contradiction. The results indicated that people did not follow any of four formal definitions of minimal change on these problems. The new information and the contradiction it offered was not, for example, used to select a particular model of the initial belief state as a way of reconciling the contradiction. The preferred revision was to retain only those initial sentences that had the same, unambiguous truth value within and across both the initial and new information sets. The study and results are presented in the context of certain logic‐based formalizations of belief revision, syntactic and model‐theoretic representations of belief states, and performance models of human deduction. Principles by which some types of sentences might be more “entrenched” than others in the face of contradiction are also discussed from the perspective of induction and theory revision. (shrink)

This paper defends an account of full belief, including an account of its relationship to credence. Along the way, I address several familiar and difficult questions about belief. Does fully believing a proposition require having maximal confidence in it? Are rational beliefs closed under entailment, or does the preface paradox show that rational agents can believe inconsistent propositions? Does whether you believe a proposition depend partly on your practical interests? My account of belief resolves the tension between conflicting (...) answers to these questions that have been defended in the literature. In addition, my account complements fruitful probabilistic theories of assertion and knowledge. (shrink)

Some eliminativists have predicted that a developed neuroscience will eradicate the principles and theoretical kinds (belief, desire, etc.) implicit in our ordinary practices of mental state attribution. Prevailing defenses of common-sense psychology infer its basic integrity from its familiarity and instrumental success in everyday social commerce. Such common-sense defenses charge that eliminativist arguments are self-defeating in their folk psychological appeal to the belief that eliminativism is true. I argue that eliminativism is untouched by this simple charge of inconsistency, and introduce (...) a different dialectical strategy for arguing against the eliminativist. In keeping with the naturalistic trend in the sociology and philosophy of science, I show that neuroscientists routinely rely on folk psychological procedures of intentional state attribution in applying epistemically reliable standards of scientific evaluation. These scientific contexts place ordinary procedures of attribution under greater stress, producing evidence of folk psychological success that is less equivocal than the evidence in mundane settings. Therefore, the dependence of science on folk psychology, when combined with an independently plausible explanatory constraint on reduction and an independently motivated notion of theoretical stress, allows us to reconstitute the charge of (neurophilic) eliminativist inconsistency in a more sophisticated form. (shrink)

In this paper two systems of AGM-like Paraconsistent Belief Revision are overviewed, both defined over Logics of Formal Inconsistency (LFIs) due to the possibility of defining a formal consistency operator within these logics. The AGM° system is strongly based on this operator and internalize the notion of formal consistency in the explicit constructions and postulates. Alternatively, the AGMp system uses the AGM-compliance of LFIs and thus assumes a wider notion of paraconsistency - not necessarily related to the notion of formal (...) consistency. (shrink)

ABSTRACT To have a coherent picture of Wang Chong’s Lunheng is difficult. Some of Lunheng’s chapters obviously show Wang’s hostility to a large part of the folklore (including the social institutions based on it) and traditional philosophical texts. In some other chapters, however, Wang appears to be more sympathetic to the social institutions related to folk religious beliefs. Esther Sunkyung Klein & Colin Klein attempt to explain this prima facie inconsistency in terms of ‘piecemeal non-reductionism’, which roughly means that (...) Wang would take any testimonial belief for granted until he can find a defeater of such a belief. But this explanation merely depicts Wang as a defeater-seeker rather than a thinker looking for philosophical grounds of his claims in a more positive manner. In contrast, in this paper, I intend to attribute the following epistemological thesis to Wang: A testimonial belief taken from classics or folklore will be judged as unjustified if the knowledge attributor finds a non-negligible defeater of it, and such an attributor would feel more sympathetic to the target belief if it can be at least prima facie justified in the light of analogical reasoning. (shrink)

Isaac Levi has claimed that our reliance on the testimony of others, and on the testimony of the senses, commonly produces inconsistency in our set of full beliefs. This happens if what is reported is inconsistent with what we believe to be the case. Drawing on a conception of the role of beliefs in inquiry going back to Dewey, Levi has maintained that the inconsistent belief corpus is a state of ``epistemic hell'': it is useless as (...) a basis for inquiry and deliberation. As he has also noticed, the compatibility of these two elements of his pragmatist epistemology could be called into question. For if inconsistency means hell, how can it ever be rational to enter that state, and on what basis could we attempt to regain consistency? Levi, nonetheless, has tried to show that the conflict is only apparent and that no changes of his theory are necessary. In the main part of the paper I argue, by contrast, that his attempts to reconcile these components of his view are unsuccessful.The conflict is real andthus presents a genuine threat to Deweyan pragmatism, as understood by Levi. After an attempt to pinpoint exactly where the source of the problem lies, I explore some possibilities for how to come to grips with it. I conclude that Levi can keep his fundamental thesis concerning the role of beliefs in inquiry and deliberation, provided that he (i) gives up the view that the agent can legitimately escape from inconsistency, and (ii) modifies his account of prediction alias deliberate expansion by acknowledging a third desideratum, besides probability and informational value, namely, not to cause permanent breakdown further down the line of inquiry. The result is a position which is more similar to Peter Gärdenfors's than is Levi's original theory, while retaining the basic insights of the latter. (shrink)

We cannot know something unless it is true. The things that we know, therefore, must be logically consistent. Moreover, we cannot know something unless we are justified in believing it. But it does not obviously follow that the things that we are justified in believing must be consistent with each other. For we can be justified in believing something that turns out to be false. Knowledge entails truth and hence consistency. Rationally justified belief does not entail truth and it may (...) not entail consistency.Knowledge, however, requires especially good justification. We can have reason to believe something that happens to be true, even good reason, without our belief being so well-grounded that we know it to be true. (shrink)

Most opposition to induced abortion turns on the belief that human fetuses are persons from conception. On this view, the moral status of the fetus alone requires those in a position to provide aid—gestational mothers—to make tremendous sacrifices to benefit the fetus. Recently, critics have argued that this pro-life position requires more than opposition to induced abortion. Pro-life theorists are relatively silent on the issues of spontaneous abortion, surplus in vitro fertilisation human embryos, and the suffering and death of born (...) persons due to lack of access to food, shelter and medical care. Colgrove et al call such arguments inconsistency arguments, arguing they ‘do not matter’ and mischaracterise them as ad hominem attacks. Here, I argue these are better understood as moral dilemmas. While some critics argue pro-life inaction is evidence that they do not really believe human fetuses are persons, I contend this inaction is likely the result of resolvable confusion rather than moral negligence. (shrink)

This paper demonstrates that there is an inconsistency in functionalism in psychology and philosophy of mind. Analogous inconsistencies can be expected in functionalisms in biology and social theory. (edited).

Abstract In this paper I discuss one apparent counterexample to the rationality constraint on belief ascription. The fact that there are inconsistent believers does not seem compatible with the idea that only rational creatures can be ascribed beliefs. I consider Davidson's explanation of the possibility of inconsistent believers and claim that it involves a reformulation of the rationality constraint in terms of the believers' subscription to norms of rationality. I shall argue that Davidson's strategy is partially successful, (...) but that the emphasis on the notion of subscription badly fits with the motivations behind his theory of interpretation. (shrink)

Two systems of belief change based on paraconsistent logics are introduced in this article by means of AGM-like postulates. The first one, AGMp, is defined over any paraconsistent logic which extends classical logic such that the law of excluded middle holds w.r.t. the paraconsistent negation. The second one, AGMo , is specifically designed for paraconsistent logics known as Logics of Formal Inconsistency (LFIs), which have a formal consistency operator that allows to recover all the classical inferences. Besides the three usual (...) operations over belief sets, namely expansion, contraction and revision (which is obtained from contraction by the Levi identity), the underlying paraconsistent logic allows us to define additional operations involving (non-explosive) contradictions. Thus, it is defined external revision (which is obtained from contraction by the reverse Levi identity), consolidation and semi-revision, all of them over belief sets. It is worth noting that the latter operations, introduced by S. Hansson, involve the temporary acceptance of contradictory beliefs, and so they were originally defined only for belief bases. Unlike to previous proposals in the literature, only defined for specific paraconsistent logics, the present approach can be applied to a general class of paraconsistent logics which are supraclassical, thus preserving the spirit of AGM. Moreover, representation theorems w.r.t. constructions based on selection functions are obtained for all the operations. (shrink)

This comment raises two worries for Crane’s view of religious beliefs and their contents. First, I argue that his appeal to inferentialism about the contents of dispositional beliefs cannot fully avoid the problem of inconsistent beliefs. For the same problem can be raised for occurrent thought, and the inferentialist solution is not available there. Second, I argue that religious beliefs differ from ordinary beliefs with respect to their justification in cases of peer disagreements. This (...) suggests that noncognitivism about religious beliefs, which Crane opposes, is the correct view after all. (shrink)

The belief bias in reasoning occurs when individuals are more willing to accept conclusions that are consistent with their beliefs than conclusions that are inconsistent. The present study...

ABSTRACT Although much effort has been expended by researchers in trying to maintain a consistent belief base in formalizing commonsense reasoning, there is some evidence that the nature of commonsense reasoning itself brings inconsistencies with it. I will outline a number of sources of such inconsistencies, and discuss why they appear unavoidable. I will also suggest that, far from being a roadblock to effective commonsense, (detected) inconsistencies are often a reasoner's best guide to what to do next.

It is commonly assumed that if one's beliefs are epistemically rational, then those beliefs must at least be consistent with one another. I argue that this assumption is false. I argue that it can be epistemically rational for a person to believe an inconsistent set of statements. I argue further that while one can rationally believe an inconsistent set of statements, one cannot rationally believe a set of statements that she or he knows to be (...) class='Hi'>inconsistent. ;In opposition, versions of the "Preface Paradox" and the "Lottery Paradox" seem to show that one can be epistemically rational in believing a set of statements that she or he knows is inconsistent. More specifically, these paradoxes seem to show that one can be epistemically rational in believing a set of statements of the form . ;I carefully examine both paradoxes and argue for solutions that preserve all of the epistemic principles that generate these paradoxes and the assumption that it is not rational to believe a set of statements that is known to be inconsistent. (shrink)

Reasoning and change over inconsistent knowledge bases is of utmost relevance in areas like medicine and law. Argumentation may bring the possibility to cope with both problems. Firstly, by constructing an argumentation framework from the inconsistent KB, we can decide whether to accept or reject a certain claim through the interplay among arguments and counterarguments. Secondly, by handling dynamics of arguments of the AF, we might deal with the dynamics of knowledge of the underlying inconsistent KB. Dynamics (...) of arguments has recently attracted attention and although some approaches have been proposed, a full axiomatization within the theory of belief revision was still missing. A revision arises when we want the argumentation semantics to accept an argument. Argument Theory Change encloses the revision operators that modify the AF by analyzing dialectical trees—arguments as nodes and attacks as edges—as the adopted argumentation semantics. In this article, we present a simple approach to ATC based on propositional KBs. This allows to manage change of inconsistent KBs by relying upon classical belief revision, although contrary to it, consistency restoration of the KB is avoided. Subsequently, a set of rationality postulates adapted to argumentation is given, and finally, the proposed model of change is related to the postulates through the corresponding representation theorem. Though we focus on propositional logic, the results can be easily extended to more expressive formalisms such as first-order logic and description logics, to handle evolution of ontologies. (shrink)

Every theory of rationality worth taking seriously implies that it is in some way irrational to accept contradictions. In this essay, the author examines how exactly this basic idea should be spelled out. He argues for two claims. First, it is not practically irrational to accept a contradiction in the sense of causing oneself to have contradictory beliefs. Second, it is moreover not theoretically irrational to accept a contradiction in the sense of having contradictory beliefs, if the contradictoriness (...) of the relevant beliefs is inaccessible to the person. The contradictoriness of a set of beliefs is accessible to a person only if this person possesses the general cognitive capacities to realise that the beliefs are contradictory. (shrink)

There are two ways of representing rational belief: qualitatively as yes-or-no belief, and quantitatively as degrees of belief. Standard rationality conditions are: consistency and logical closure, for qualitative belief, satisfaction of the probability axioms, for quantitative belief, and a relationship between qualitative and quantitative beliefs in accordance with the Lockean thesis. In this paper, it is shown that these conditions are inconsistent with each of three further rationality conditions: fallibilism, open-mindedness, and invariance under independent conceptual expansions. Restrictions of (...) the Lockean thesis that have been suggested in the literature cannot remove the inconsistency. In the outlook we discuss two alternative ways of dealing with this problem: restricting conjunctive closure or going for a dual system account. (shrink)

"Paraconsistent Belief Revision Based on a Formal Consistency Operator" delves into Belief Revision—a significant area of research in Formal Philosophy that uses logic to model the ways in which human and artificial agents modify their beliefs in response to new information and examines how these changes can be considered rational. -/- Originally authored as a PhD thesis (previously published in Portuguese), this work provides a novel epistemic interpretation of Paraconsistency through Paraconsistent Belief Revision systems. It explores the concept of (...) paraconsistency from the standpoint of epistemic attitudes of acceptance and rejection. -/- This work challenges the traditional notion that accepting a new belief requires retracting its negation from the current epistemic state. The author contends that such reflexive retraction goes against the principle of informational economy, which is a crucial aspect of rationality in the context of belief change. Consequently, the phenomenon of paraconsistency is further examined from this fresh perspective of belief change, shedding light on the complexities of the Logics of Formal Inconsistency (LFIs). These LFIs provide the foundational logic, offering a comprehensive framework for understanding and implementing paraconsistent principles within belief revision systems. -/- This thesis was supervised by Marcelo Esteban Coniglio and co-supervised by Márcio Moretto Ribeiro, as part of Rafael Rodrigues Testa's doctoral studies at the University of Campinas (Unicamp), Brazil. (shrink)

In this paper I present an argument for belief in inconsistent objects. The argument relies on a particular, plausible version of scientific realism, and the fact that often our best scientific theories are inconsistent. It is not clear what to make of this argument. Is it a reductio of the version of scientific realism under consideration? If it is, what are the alternatives? Should we just accept the conclusion? I will argue (rather tentatively and suitably qualified) for a (...) positive answer to the last question: there are times when it is legitimate to believe in inconsistent objects. (shrink)

In this paper, I argue that the following claims are jointly inconsistent: (1) that an agent’s justification for belief, if it’s constituted by evidence, depends on the profile of her background beliefs, (2) that whether or not a group believes a proposition is solely dependent on whether the proposition is jointly accepted by its members, and (3) that prototypical group beliefs are justified. I also raise objections to attempts to resolve the tension by retaining (2) and (3). (...) The upshot is a novel objection to the Joint Acceptance Account of group belief since it seems to be accompanied by a kind of skepticism. (shrink)

Is logical consistency required for a set of beliefs or propositions to be categorically coherent? An affirmative answer is often assumed by mainstream epistemologists, and yet it is unclear why. Cases like the lottery and the preface call into question the assumption that beliefs must be consistent in order to be epistemically rational. And thus it is natural to wonder why all inconsistent sets of propositions are incoherent. On the other hand, Easwaran and Fitelson have shown that (...) particular kinds of inconsistency entail the epistemically ‘irrationality’ of holding certain sets of beliefs. In cases of the latter kind of inconsistency, it seems more reasonable to insist that such sets of beliefs or propositions are categorically incoherent. What the precise relationship is between coherence and consistency depends on the nature of the coherence relation. We shall examine recent attempts to explicate the coherence relation in terms of probabilistic measures of confirmation or agreement to see what they can teach us about the relationship between coherence and consistency. We shall show that some probabilistic measures of coherence allow for inconsistent sets to be categorically coherent, while satisfying plausible epistemic rationality constraints. Other probabilistic measures of coherence impose very strong logical consistency requirements, and some measures are tolerant of most forms of inconsistency. As we try to understand what distinguishes coherence measures in this respect, we will also draw some important lessons about Bayesian confirmation measures and differences in the way that they treat contradictory propositions. (shrink)