According to the so-called ‘Taking Condition’ (a label due to Boghossian 2014) on inference, for a response R in circumstances C to count as an instance of reasoning or inferring, it must be the case that the agent’s taking it that R is warranted or justified in C plays (the right sort of) explanatory role in her R-ing. The Taking Condition has come under much criticism in the theory of reasoning. While I believe that these criticisms can be answered, my (...) aim in this paper is to build a positive case for the Taking Condition. More specifically, I argue that views based on the Taking Condition do a much better job accounting for crucial features of reasoning—especially once we recognize the pervasiveness and significance of defeasibility in our reasoning. (shrink)

The study of defeasible reasoning unites epistemologists with those working in AI, in part, because both are interested in epistemic rationality. While it is traditionally thought to govern the formation and (with)holding of beliefs, epistemic rationality may also apply to the interrogative attitudes associated with our core epistemic practice of inquiry, such as wondering, investigating, and curiosity. Since generally intelligent systems should be capable of rational inquiry, AI researchers have a natural interest in the norms that govern interrogative attitudes. Following (...) its recent coinage, we use the term ``zetetic'' to refer to the properties and norms associated with the capacity to inquire. In this paper, we argue that zetetic norms can be modeled via defeasible inferences to and from questions---a.k.a erotetic inferences---in a manner similar to the way norms of epistemic rationality are represented by defeasible inference rules. We offer a sequent calculus that accommodates the unique features of ``erotetic defeat" and that exhibits the computational properties needed to inform the design of zetetic agents. The calculus presented here is an improved version of the one presented in Millson (2019), extended to cover a new class of defeasible erotetic inferences. (shrink)

Reductive intellectualists (e.g., Stanley & Williamson 2001; Stanley 2011a; 2011b; Brogaard 2008; 2009; 2011) hold that knowledge-how is a kind of knowledge-that. If this thesis is correct, then we should expect the defeasibility conditions for knowledge-how and knowledge-that to be uniform—viz., that the mechanisms of epistemic defeat which undermine propositional knowledge will be equally capable of imperilling knowledge-how. The goal of this paper is twofold: first, against intellectualism, we will show that knowledge-how is in fact resilient to being undermined (...) by the very kinds of traditional (propositional) epistemic defeaters which clearly defeat the items of propositional knowledge which intellectualists identify with knowledge-how. Second, we aim to fill an important lacuna in the contemporary debate, which is to develop an alternative way in which epistemic defeat for knowledge-how could be modelled within an anti-intellectualist framework. (shrink)

The paper investigates the epistemological and communicative competences the experts need to use and communicate evidence in the reasoning process leading to diagnosis. The diagnosis and diagnosis communication are presented as intertwined processes that should be jointly addressed in medical consultations, to empower patients’ compliance in illness management. The paper presents defeasible reasoning as specific to the diagnostic praxis, showing how this type of reasoning threatens effective diagnosis communication and entails that we should understand diagnostic evidence as defeasible as well. (...) It argues that metaphors might be effective communicative devices to let the patients understand the relevant defeasors in the diagnostic reasoning process, helping to improve effective diagnosis communication, and also encouraging a change in patients’ beliefs and attitudes on their own experience of illness and illness’ management. (shrink)

This work explores some ways in which logics for defeasible reasoning can be applied to questions in epistemology. It's naturally thought of as developing four applications: The first is concerned with simple epistemic rules, such as "If you perceives that X, then you ought to believe that X" and "If you have outstanding testimony that X, then you ought to believe that X." Anyone who thinks that such rules have a place in our accounts of epistemic normativity must explain what (...) happens in cases where they come into conflict —such as one where you perceive a red object and are told that it is blue. The literature has gone in two directions: The first suggests that rules have built-in unless-clauses specifying the circumstances under which they fail to apply; the second that rules do not specify what attitudes you ought to have, but only what counts in favor or against having those attitudes. I express these two different ideas in a defeasible logic framework and demonstrate that there's a clear sense in which they are equivalent. The second application uses a defeasible logic to solve an important puzzle about epistemic rationality, involving higher-order evidence, or, roughly, evidence about our capacities for evaluating evidence. My solution has some affinities with the so-called conflicting-ideals view. The third application, then, is a characterization of this view in logical terms: I suggest that it should be thought of as an unconventional metaepistemological view, according to which epistemic requirements are not exceptionless, but defeasible and governed by a comparatively weak logic. Finally, the fourth application is in the burgeoning debate about the epistemic significance of disagreement. The intuitive conciliatory views say, roughly, that you ought to become less confident in your take on some question X, if you learn that an epistemic equal disagrees with you about X. I propose to think of conciliationism as a defeasible reasoning policy, develop a mathematically precise model of it, and use it to solve one of the most pressing problems for conciliatory views: Given that there are disagreements about these views themselves, they can self-defeat and issue inconsistent recommendations. (shrink)

This is a survey article about epistemic defeaters: what is defeated, how defeaters work, different kinds of defeaters, indefeasibility and how defeaters fit into epistemic internalism and externalism.

In this article, we present an analysis of defeasible generalizations -- generalizations which are essentially exception-laden, yet genuinely explanatory -- in terms of various notions of privileged conditions. We argue that any plausible epistemology must make essential use of defeasible generalizations so understood. We also consider the epistemic significance of the sort of understanding of context that is required for understanding of explanatory defeasible generalizations on any topic.

In defeasible reasoning, initially drawn conclusions can be withdrawn in light of new information. In this paper, we examine how the conclusions drawn from conditionals describing positive or negative situations can be defeated by subsequent negative or positive information, respectively. Participants were confronted with conditionals of the form “If [situation], then I am happy/sad” which were either followed by no additional information or by additional information describing situations of the same or the opposite valence. The participant's task was to decide (...) on a question asking for a possible conclusion (“Am I happy?” vs. “Am I sad?”). We found a negativity bias in defeasible reasoning: negative information defeated positively charged conclusions more strongly than positive information defeated negatively charged conclusions. We discuss our results in relation to the new psychology of reasoning. (shrink)

The applicability of Bayesian conditionalization in setting one’s posterior probability for a proposition, α, is limited to cases where the value of a corresponding prior probability, PPRI(α|∧E), is available, where ∧E represents one’s complete body of evidence. In order to extend probability updating to cases where the prior probabilities needed for Bayesian conditionalization are unavailable, I introduce an inference schema, defeasible conditionalization, which allows one to update one’s personal probability in a proposition by conditioning on a proposition that represents a (...) proper subset of one’s complete body of evidence. While defeasible conditionalization has wider applicability than standard Bayesian conditionalization (since it may be used when the value of a relevant prior probability, PPRI(α|∧E), is unavailable), there are circumstances under which some instances of defeasible conditionalization are unreasonable. To address this difficulty, I outline the conditions under which instances of defeasible conditionalization are defeated. To conclude the article, I suggest that the prescriptions of direct inference and statistical induction can be encoded within the proposed system of probability updating, by the selection of intuitively reasonable prior probabilities. (shrink)

For some of us, the defeasibility theory of knowledge remains the most plausible approach to the Gettier Problem. Epistemological fashion and faded memories notwithstanding, persuasive objections to the theory are very hard to find. The most impressive of those objections to the theory that have hitherto gone unanswered are examined and rejected here. These are objections put forward by Richard Feldman, Richard Foley, and John Turri. While these are all interesting, the objection recently put forward by Turri is, we (...) think, by far, the most serious threat to the theory that we have seen in a long time. A successful reply to it requires a surprising amount of care, as it turns out. If tenable, Turri's objection deals a devastating blow to the theory developed by Roderick Chisholm, Keith Lehrer, Peter Klein, Marshall Swain, Risto Hilpinen, John Pollock, and Paul Moser, among others. Under scrutiny, however, the threat proves illusory. It results from inattention to a crucial, but relatively subtle, aspect of.. (shrink)

This paper builds on a previous discussion of Stephen Mumford’s rejection of what he takes to be David Best’s argument for a distinction between purposive and aesthetic sports. That discussion concluded that Mumford’s argument misses its target, but closed by introducing a possible alternative argument, not made by Mumford, that might be thought to have the potential to secure Mumford’s conclusion. This paper considers that alternative argument, namely, the thought that the ascription of psychological predicates conceived of in terms of (...) defeasible criteria that constitute logically good evidence could preserve Best’s claim to be making a logical point while allowing a place for intention in relation to aims and purposes in sport. It is argued that the relationship between rules and intention is such that this alternative argument cannot secure Mumford’s conclusion. (shrink)

Defeasible rules are said to allow for the following two-staged sequence, viz., that p → q and yet p & r → not-q. This is puzzling because in the logic of conditionals the sufficiency of p for q cannot normally be undermined if one adds to the antecedent a further proposition r. Critics argue that the better approach to comprehending defeasibility is explicitly to represent the limiting factor r in a single-stage articulation of the rule, viz., as p & (...) not-r → q. This is a more complete statement of the rule; where the old rule announced, confidently and without qualification, that in circumstances or class of cases p consequence q follows, the new rule admits from the outset that q only follows if we add the qualifier that limits the antecedent circumstances to the smaller class of cases p & not-r. This is not only more complete, the critics argue, it is also a more accurate or truthful statement of the rule. The rule p → q, articulated at the first stage of the defeasible process, is only a pretender encountered along the way to this more complete truth. In this paper I show how, and why, contrary to the critics, the process of private law adjudication supports the multi-staged structure and representation of defeasible legal rules. What matters when one party makes a claim against another party is not so much that the claim is true (or even that it is advanced as a legitimate claim under the rule that is most likely to be true), but rather that the claim is of the sort that the party can justifiably say is true. The latter, at least, is what carries the plaintiff past the initial burden of proof, and what calls for the defendant to reply if the plaintiff is not to carry the day. I illustrate the argument by way of the court’s reluctance in a tort case to entertain a purely statistical basis for a plaintiff’s claim that the defendant has caused her injury. Rather, the court will insist on direct evidence that appears to arise out of the particular circumstances of the case as the plaintiff alleges them to be, and even if, as a purely statistical matter, the latter sort of claim is less likely to be true than the claim grounded in pure statistical likelihood. I relate this argument for defeasible rules (and against rules that are more truthful) to some important arguments offered by the philosopher Stephen Darwall in his recent book The Second Person Viewpoint. Private law’s defeasible rules, I argue, capture the special respect (and interpersonal accountability) that attaches only to rights arising out of “second personal” claiming (and counterclaiming) and which are not realizable merely as a matter of “third personal” (moral) truth. (shrink)

Defeasibility, most generally speaking, means that given some set of conditions A, something else B will hold, unless or until defeating conditions C apply. While the term was introduced into philosophy by legal philosopher H.L.A. Hart in 1949, today, the concept of defeasibility is employed in many different areas of philosophy. This volume for the first time brings together contributions on defeasibility from epistemology , legal philosophy and ethics and the philosophy of action . The volume ends (...) with an extensive bibliography. (shrink)

According to intentionalism, perceptual experience is a mental state with representational content. When it comes to the epistemology of perception, it is only natural for the intentionalist to hold that the justificatory role of experience is at least in part a function of its content. In this paper, I argue that standard versions of intentionalism trying to hold on to this natural principle face what I call the “defeasibility problem”. This problem arises from the combination of standard intentionalism with (...) further plausible principles governing the epistemology of perception: that experience provides defeasible justification for empirical belief, and that such justification is best construed as probabilification. After exploring some ways in which the standard intentionalist could deal with the defeasibility problem, I argue that the best option is to replace standard intentionalism by what I call “phenomenal intentionalism”. Where standard intentionalism construes experiences as of p as having the content p, phenomenal intentionalism construes experiences as of p as having “phenomenal” or “looks contents”: contents of the form Lp. (shrink)

Argumentation represents a way of reasoning over a knowledge base containing possibly incomplete and/or inconsistent information, to obtain useful conclusions. As a reasoning mechanism, the way an argumentation reasoning engine reaches these conclusions resembles the cognitive process that humans follow to analyze their beliefs; thus, unlike other computationally reasoning systems, argumentation offers an intellectually friendly alternative to other defeasible reasoning systems. LogicProgrammingisacomputationalparadigmthathasproducedcompu- tationallyattractivesystemswithremarkablesuccessinmanyapplications. Merging ideas from both areas, Defeasible Logic Programming offers a computational reasoning system that uses an argumentation engine (...) to obtain answers from a knowledge base represented using a logic programming language extended with defeasible rules. This combination of ideas brings about a computationally effective system together with a human-like reasoning model facilitating its use in applications. (shrink)

The notions of defeasibility and defeasible reasoning have generated a great deal of interest in various research communities. Here I want to focus on their use in logic and argumentation studies. I will approach these topics from the perspective of an informal logician who finds himself struggling with some issues that surround the idea of and the deployment of the concept of defeasibility. My intention is to make those struggles as clear as I can.

The paper is motivated by the need of accounting for the practical syllogism as a piece of defeasible reasoning. To meet the need, the paper first refers to ranking theory as an account of defeasible descriptive reasoning. It then argues that two kinds of ought need to be distinguished, purely normative and fact-regarding obligations. It continues arguing that both kinds of ought can be iteratively revised and should hence be represented by ranking functions, too, just as iteratively revisable beliefs. Its (...) central proposal will then be that the fact-regarding normative ranking function must be conceived as the sum of a purely normative ranking function and an epistemic ranking function. The distinctions defends this proposal with a comparative discussion of some critical examples and some other distinctions made in the literature. It gives a more rigorous justification of this proposal. Finally, it starts developing the logic of purely normative and of fact-regarding normative defeasible reasoning, points to the difficulties of completing the logic of the fact-regarding side, but reaches the initial aim of accounting for the defeasible nature of the practical syllogism. (shrink)

Relevant to philosophy, law, management, and artificial intelligence, these papers explore the applicability of nonmonotonic or defeasible logic to normative reasoning. The resulting systems purport to solve well-known deontic paradoxes and to provide a better treatment than classical deontic logic does of prima facie obligation, conditional obligation, and priorities of normative principles.

The general conditions of epistemic defeat are naturally represented through the interplay of two distinct kinds of entailment, deductive and defeasible. Many of the current approaches to modeling defeasible reasoning seek to define defeasible entailment via model-theoretic notions like truth and satisfiability, which, I argue, fails to capture this fundamental distinction between truthpreserving and justification-preserving entailments. I present an alternative account of defeasible entailment and show how logic programming offers a paradigm in which the distinction can be captured, allowing for (...) the modeling of a larger range of types of defeat. This is possible through a natural extension of the declarative and procedural semantics of Horn clauses. (shrink)

There was a long tradition in philosophy according to which good reasoning had to be deductively valid. However, that tradition began to be questioned in the 1960’s, and is now thoroughly discredited. What caused its downfall was the recognition that many familiar kinds of reasoning are not deductively valid, but clearly confer justification on their conclusions. Here are some simple examples.

While defeasibility in legal reasoning has been the subject of recent scholarship, it has yet to be studied in the context of judicial opinion. Yet, being subject to appeal, judicial decisions can default for a variety of reasons. Prakken (2001) argued that the defeasibility affecting reasoning involved in adversarial legal argumentation is best analysed as procedural rather than logical. In this paper we argue that the defeasibility of ratio decendi is similarly best explained and modeled in a (...) procedural and dialectical framework. We propose that appeals are best understood as meta-dialogues about the reasoned dialogue occurring in the initial trial. (shrink)

We contend that it is possible to argue reasonably for and against arguments from classifications and definitions, provided they are seen as defeasible (subject to exceptions and critical questioning). Arguments from classification of the most common sorts are shown to be based on defeasible reasoning of various kinds represented by patterns of logical reasoning called defeasible argumentation schemes. We show how such schemes can be identified with heuristics, or short-cut solutions to a problem. We examine a variety of arguments of (...) this sort, including argument from abductive classification, argument from causal classification, argument from analogy-based classification and arguments from classification based on generalizations. (shrink)

This paper examines a leading traditional account of memory knowledge. (A “traditional” account of memory knowledge locates whatever positive justification there may be for the belief which constitutes that knowledge in a present memory-impression.) The paper (1) presents a pair of cases designed to show that Carl Ginet’s four-part defeasibility-type definition of memory knowledge that p is either too weak or too strong, and (2) suggests how these cases could be handled by one sort of non-traditional account.

This is a reply to a paper by Graham Oppy in the July, 1999 issue of this journal, “Koons’ Cosmological Argument.” Recent work in defeasible or nonmonotonic logic means that the cosmological argument can be cast in such a way that it does not presuppose that every contingent situation, without exception, has a cause. Instead, the burden of proof is shifted to the skeptic, who must produce positive reasons for thinking that the cosmos is an exception to the defeasible law (...) of causality. I show how Oppy’s critique can be turned into a plausible rebuttal of my argument. However, this rebuttal can be set aside when the original argument is supplemented by a plausible account of the nature of causal priority. Several independent lines of argument in support of this account are outlined. (shrink)

The question addressed in this paper is how the degree of justification of a belief is determined. A conclusion may be supported by several different arguments, the arguments typically being defeasible, and there may also be arguments of varying strengths for defeaters for some of the supporting arguments. What is sought is a way of computing the “on sum” degree of justification of a conclusion in terms of the degrees of justification of all relevant premises and the strengths of all (...) relevant reasons. (shrink)

The paper is motivated by the need of accounting for the practical syllogism as a piece of defeasible reasoning. To meet the need, the paper first refers to ranking theory as an account of defeasible descriptive reasoning. It then argues that two kinds of ought need to be distinguished, purely normative and fact-regarding obligations (in analogy to intrinsic and extrinsic utilities). It continues arguing that both kinds of ought can be iteratively revised and should hence be represented by ranking functions, (...) too, just as iteratively revisable beliefs. Its central proposal will then be that the fact-regarding normative ranking function must be conceived as the sum of a purely normative ranking function and an epistemic ranking function (as suggested in qualitative decision theory). The distinctions defends this proposal with a comparative discussion of some critical examples and some other distinctions made in the literature. It gives a more rigorous justification of this proposal. Finally, it starts developing the logic of purely normative and of fact-regarding normative defeasible reasoning, points to the difficulties of completing the logic of the fact-regarding side, but reaches the initial aim of accounting for the defeasible nature of the practical syllogism. (shrink)

In his recent book Albert Casullo rejects the claim that if a belief is defeasible by non-experiential evidence then it is defeasible by experiential evidence. This claim is a crucial premise in a simple argument for the experiential defeasibility of a priori justification. I defend the premise against Casullo's objection, the main problem with which is that he does not take into account the evidential role of multiple corroborating sources of testimony. I conclude that the crucial premise is true (...) and that the simple argument is sound; thus many of our a priori justified beliefs are experientially defeasible. (shrink)

It is argued, on the basis of new counterexamples, that neither knowledge nor epistemic justification (or epistemic rationality ) can reasonably be thought to be closed under logical implication. The argument includes an attempt to reconcile the fundamental intuitions of the opposing parties in the debate.

Defeasible argumentation has been applied successfully in several real-world domains in which it is necessary to handle incomplete and contradictory information. In recent years, there have been interesting attempts to carry out argumentation processes supported by massive repositories developing argumentative reasoning applications. One of such efforts builds arguments by retrieving information from relational databases using the DBI-DeLP framework; this article presents eDBI-DeLP, which extends the original DBI-DeLP framework by providing two novel aspects which refine the interaction between DeLP programs and (...) relational databases. First, we expand the expressiveness of dbi-delp programs by providing ways of controlling how the information in databases is recovered; this is done by introducing filters that enable an improved fine-grained control on the argumentation processes which become useful in applications, providing the semantics and the implementation of such filters. Second, we introduce an argument comparison criterion which can be adjusted at the level of literals to model particular features such as credibility and topic expertise, among others. These new tools can be particularly useful in environments such as medical diagnosis expert systems, decision support systems, or recommender systems based on argumentation, where datasets are often provided in the form of relational databases. (shrink)

This paper argues that some traditional fallacies should be considered as reasonable arguments when used as part of a properly conducted dialog. It is shown that argumentation schemes, formal dialog models, and profiles of dialog are useful tools for studying properties of defeasible reasoning and fallacies. It is explained how defeasible reasoning of the most common sort can deteriorate into fallacious argumentation in some instances. Conditions are formulated that can be used as normative tools to judge whether a given defeasible (...) argument is fallacious or not. It is shown that three leading violations of proper dialog standards for defeasible reasoning necessary to see how fallacies work are: (a) improper failure to retract a commitment, (b) failure of openness to defeat, and (c) illicit reversal of burden of proof. (shrink)

I propose a novel solution to the Sorites Paradox. The account vindicates the tolerance of vague predicates in a way that properly addresses the normativity of vagueness while avoiding sorites contradiction, by treating sorites reasoning as a type of defeasible reasoning. I show how this can be done within the setting of a nonmonotonic deontic logic. Central to the proposal is its deontic interpretation of tolerance. I draw a key distinction between two types of tolerance, based on different deontic notions, (...) and show how the account captures key differences between these types of sorites reasoning. I compare the resulting theory to various existing contextualist proposals and argue that it better accounts for the normative aspects of sorites reasoning. (shrink)

The paper starts by describing and clarifying what Williamson calls the consequence fallacy. I show two ways in which one might commit the fallacy. The first, which is rather trivial, involves overlooking background information; the second way, which is the more philosophically interesting, involves overlooking prior probabilities. In the following section, I describe a powerful form of sceptical argument, which is the main topic of the paper, elaborating on previous work by Huemer. The argument attempts to show the impossibility of (...) defeasible justification, justification based on evidence which does not entail the (allegedly) justified proposition or belief. I then discuss the relation between the consequence fallacy, or some similar enough reasoning, and that form of argument. I argue that one can resist that form of sceptical argument if one gives up the idea that a belief cannot be justified unless it is supported by the totality of the evidence available to the subject—a principle entailed by many prominent epistemological views, most clearly by epistemological evidentialism. The justification, in the relevant cases, should instead derive solely from the prior probability of the proposition. A justification of this sort, that does not rely on evidence, would amount to a form of entitlement, in (something like) Crispin Wright’s sense. I conclude with some discussion of how to understand prior probabilities, and how to develop the notion of entitlement in an externalist epistemological framework. (shrink)

In concrete applications of probability, statistical investigation gives us knowledge of some probabilities, but we generally want to know many others that are not directly revealed by our data. For instance, we may know prob(P/Q) (the probability of P given Q) and prob(P/R), but what we really want is prob(P/Q& R), and we may not have the data required to assess that directly. The probability calculus is of no help here. Given prob(P/Q) and prob(P/R), it is consistent with the probability (...) calculus for prob(P/Q& R) to have any value between 0 and 1. Is there any way to make a reasonable estimate of the value of prob(P/Q& R) 1 A related problem occurs when probability practitioners adopt undefended assumptions of statistical independence simply on the basis of not seeing any connection between two propositions. This is common practice, but its justification has eluded probability theorists, and researchers are typically apologetic about making such assumptions. Is there any way to defend the practice? This paper shows that on a certain conception of probability—nomic probability—there are principles of "probable probabilities" that license inferences of the above sort. These are principles telling us that although certain inferences from probabilities to probabilities are not deductively valid, nevertheless the second-order probability of their yielding correct results is 1. This makes it defeasibly reasonable to make the inferences. Thus I argue that it is defeasibly reasonable to assume statistical independence when we have no information to the contrary. And I show that there is a function Y(r, s, a) such that if prob(P/Q) = r, prob(P/R) = s, andprob(P/U) = a (where U is our background knowledge) then it is defeasibly reasonable to expect that prob(P/Q&R) = Y(r, s, a). Numerous other defeasible inferences are licensed by similar principles of probable probabilities. This has the potential to greatly enhance the usefulness of probabilities in practical application. (shrink)

In this paper we show how defeasible logic could formally account for the non-monotonic properties involved in motivational attitudes like intention and obligation. Usually, normal modal operators are used to represent such attitudes wherein classical logical consequence and the rule of necessitation comes into play, i.e., ⊢A/⊢ □A, that is from ⊢A derive ⊢ □A. This means that such formalisms are affected by the Logical Omniscience problem. We show that policy-based intentions exhibit non-monotonic behaviour which could be captured through a (...) non-monotonic system like defeasible logic. To this end we outline a defeasible logic of intention that specifies how modalities can be introduced and manipulated in a non-monotonic setting without giving rise to the problem of logical omniscience. In a similar way we show how to add deontic modalities defeasibly and how to integrate them with other motivational attitudes like beliefs and goals. Finally we show that the basic aspect of the BOID architecture is captured by this extended framework. (shrink)

According to intentionalism, perceptual experience is a mental state with representational content. When it comes to the epistemology of perception, it is only natural for the intentionalist to hold that the justificatory role of experience is at least in part a function of its content. In this paper, I argue that standard versions of intentionalism trying to hold on to this natural principle face what I call the “defeasibility problem”. This problem arises from the combination of standard intentionalism with (...) further plausible principles governing the epistemology of perception: that experience provides defeasible justification for empirical belief, and that such justification is best construed as probabilification. After exploring some ways in which the standard intentionalist could deal with the defeasibility problem, I argue that the best option is to replace standard intentionalism by what I call “phenomenal intentionalism”. Where standard intentionalism construes experiences as of p as having the content p, phenomenal intentionalism construes experiences as of p as having “phenomenal” or “looks contents”: contents of the form Lp. (shrink)

After the seminal work of Kraus, Lehmann and Magidor (formally known as the KLM approach) on conditionals and preferential models, many aspects of defeasibility in more complex formalisms have been studied in recent years. Examples of these aspects are the notion of typicality in description logic and defeasible necessity in modal logic. We discuss a new aspect of defeasibility that can be expressed in the case of temporal logic, which is the normality in an execution. In this contribution, (...) we take Linear Temporal Logic (LTL) as case study for this defeasible aspect. LTL has found extensive applications in Computer Science and Artificial Intelligence, notably as a formal framework for representing and verifying computer systems that vary over time. However, some systems may presents exceptions at some innocuous time points where they can be tolerated, or conversely, exceptions at other crucial time points where they need to be addressed. In order to ensure the reliability of such systems, we study a preferential extension of LTL, called defeasible linear temporal logic (LTL ~ ). In the first part of this paper, we show how semantics of KLM's preferential models can be integrated with LTL. We also discuss the addition of non-monotonic temporal operators as a way to formalise defeasible properties of these systems. The second part of this paper is a study of the satisfiability problem of LTL ~ sentences. Based on Sistla and Clarke's work on the complexity of the classical LTL language, we show the bounded-model property of two fragments of LTL ~ language. Moreover, we provide a procedure to check the satisfiability of sentences in both of these fragments. (shrink)

Joshua Thurow offers a defence of the claim that if a belief is defeasible by non-experiential evidence then it is defeasible by experiential evidence. He responds to an objection which I make against this claim, and offers two arguments in support of his own position. I show that Thurow's response misconstrues my objection, and that his supporting arguments fall short of their goal.

Discussion of the behaviour of pregnant women and mothers, in academic literature, medical advice given to mothers, mainstream media and social media, assumes that a mother who fails to do something to benefit her child is liable for moral criticism unless she can provide sufficient countervailing considerations to justify her decision. I reconstruct the normally implicit reasoning that leads to this assumption and show that it is mistaken. First, I show that the discussion assumes that if any action might benefit (...) her child, the mother has a defeasible duty to perform that action. I suggest that this assumption is implicitly supported by two arguments but that each argument is unsound. The first argument conflates moral reasons and defeasible duties; the second misunderstands the scope of a defeasible duty to benefit. This argument has important practical and theoretical implications: practically, it provides a response to a highly damaging discourse on maternal behaviour; theoretically, it provides the framework for a clearer understanding of the scope and nature of defeasible duties to benefit. (shrink)

In this paper I argue that defeasible inferences are occasion-sensitive: the inferential connections of a given claim depend on features of the circumstances surrounding the occasion of inference. More specifically, it is an occasion-sensitive matter which possible defeaters have to be considered explicitly by the premises of an inference and which possible defeaters may remain unconsidered, without making the inference enthymematic. As a result, a largely unexplored form of occasion-sensitivity arises in inferentialist theories of content that appeal to defeasible inferences.

It is argued, on the basis of new counterexamples, that neither knowledge nor epistemic justification (or “epistemic rationality”) can reasonably be thought to be closed under logical implication. The argument includes an attempt to reconcile the fundamental intuitions of the opposing parties in the debate.