In its present incarnation, OSCAR is a fully implemented programmable architecture for a rational agent. If we just focus upon the epistemic reasoning in OSCAR, we have a powerful general-purpose defeasible reasoner. The purpose of this paper is to describe that reasoner. OSCAR's defeasible reasoner is based upon seven fundamental ideas. These are (1) an argument-based account of defeasible reasoning, (2) an analysis of defeat-status given a set of interrelated arguments, (3) a general adequacy criterion for automated defeasible reasoners, called (...) “d.e.-adequacy”, (4) the claim that a generalpurpose defeasible reasoner must have the kind of structure I have called “flag-based”, (5) an algorithm for computing defeat-status, (6) an interest-driven monotonic reasoner, and (7) an account of degrees of justification, degrees of interest, and their interactions. These will each be discussed in turn. (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)

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.

Justin D’Arms and Daniel Jacobson have argued that to evaluate the funniness of a joke based on the consideration of whether it is morally appropriate to feel amused commits the “moralistic fallacy.” We offer a new and empirically informed reply. We argue that there is a way to take morality into consideration without committing this fallacy, that is, it is legitimate to say that for some people, witty but immoral jokes can fail to be funny because they are immoral. In (...) our account, one has an intramural moral reason not to feel amused if one focuses on the moral feature itself of a joke rather than the moral consequence implied in one’s reaction to the joke. When one judges a joke as not funny because of the intramural moral reason, one is in a negative emotional state with high arousal, for example, moral disgust or anger. This state is psychologically incompatible with amusement. That one has an intramural reason not to feel amused thus implies that one does not have a reason to feel amused. Moral consideration thus plays an indirect and appropriate role in the evaluation of the funniness of a joke. (shrink)

What if your peers tell you that you should disregard your perceptions? Worse, what if your peers tell you to disregard the testimony of your peers? How should we respond if we get evidence that seems to undermine our epistemic rules? Several philosophers have argued that some epistemic rules are indefeasible. I will argue that all epistemic rules are defeasible. The result is a kind of epistemic particularism, according to which there are no simple rules connecting descriptive and normative facts. (...) I will argue that this type of particularism is more plausible in epistemology than in ethics. The result is an unwieldy and possibly infinitely long epistemic rule — an Uber-rule. I will argue that the Uber-rule applies to all agents, but is still defeasible — one may get misleading evidence against it and rationally lower one’s credence in it. (shrink)

According to the Bayesian paradigm in the psychology of reasoning, the norms by which everyday human cognition is best evaluated are probabilistic rather than logical in character. Recently, the Bayesian paradigm has been applied to the domain of argumentation, where the fundamental norms are traditionally assumed to be logical. Here, we present a major generalisation of extant Bayesian approaches to argumentation that (i)utilizes a new class of Bayesian learning methods that are better suited to modelling dynamic and conditional inferences than (...) standard Bayesian conditionalization, (ii) is able to characterise the special value of logically valid argument schemes in uncertain reasoning contexts, (iii) greatly extends the range of inferences and argumentative phenomena that can be adequately described in a Bayesian framework, and (iv) undermines some influential theoretical motivations for dual function models of human cognition. We conclude that the probabilistic norms given by the Bayesian approach to rationality are not necessarily at odds with the norms given by classical logic. Rather, the Bayesian theory of argumentation can be seen as justifying and enriching the argumentative norms of classical logic. (shrink)

This paper introduces and defends the paradigm response to external world skepticism. To understand it, consider an analogy. One of the hallmarks of being a bird is an ability to fly. A penguin lacks this hallmark and thus fails to be a paradigm bird. Likewise, there are various hallmarks of knowledge. Some of your external world beliefs lack some of these hallmarks, and thus fail to be paradigm cases of knowledge. Just as the inability of penguins to fly doesn’t prevent (...) them from being birds, likewise the lack of these hallmarks doesn’t prevent your beliefs from being knowledge. It just prevents them from being paradigm cases thereof. (shrink)

I argue that our procedures for determining whether ascriptions of a predicate represent things as being a certain way are ultimately pragmatic. Pragmatic procedures are not subject to validation by the referential procedure – determining whether there is a property playing the role of its referent. Predicates can represent even if we can't provide an independent identification of its referent. For these predicates, the speakers’ knowledge of how they represent objects as being would have to be construed in terms of (...) the ascription practices they associate with the predicates. The same approach can be applied to semantic predicates, such as ‘is representational’ or ‘refers to’. They can be treated as representational even if we can't provide an independent identification of their referents. The availability of this position undermines accounts of the referents of semantic predicates in naturalistic terms. (shrink)

Primeiramente, oferecemos uma apresentação teórica da representação do pensamento prático, começando pela distinção entre silogismo dialético e silogismo demonstrativo. Fazemos referência à crítica de Toulmin contra o dedutivismo dominante de seu tempo. Em seguida, fornecemos argumentos para apoiar a relevância heurística do modelo de Toulmin para entender a discussão sobre a inclusão da lógica padrão na representação do pensamento comum. Afirmamos que o projeto analítico toulmaniano permite entender, com clareza metódica, a derrotabilidade dos argumentos do senso comum por meio da (...) investigação da noção modal de probabilidade na linguagem comum. First, we offer theoretical resemblance of the representation of practical reasoning, beginning with the distinction between demonstrative and dialectical syllogism. We make reference to the Toulmin’s critique against to the dominant deductivism in his time. Then we give arguments to sustain the heuristic relevance of Toulmin’s model to understand the discussion about the inclusion of default logics in the representation of ordinary reasoning. We assert that the Toulminian analytic design allows to understand, with methodical clarity, the defeasibility of common sense arguments by means of the investigation of the modal notion of probability in ordinary language. (shrink)

This article sketches a theory of objective probability focusing on nomic probability, which is supposed to be the kind of probability figuring in statistical laws of nature. The theory is based upon a strengthened probability calculus and some epistemological principles that formulate a precise version of the statistical syllogism. It is shown that from this rather minimal basis it is possible to derive theorems comprising (1) a theory of direct inference, and (2) a theory of induction. The theory of induction (...) is not of the familiar Bayesian variety, but consists of a precise version of the traditional Nicod Principle and its statistical analogues. (shrink)

It is argued that higher-order awareness is central to one type of everyday rationality. The author starts by specifying the target notion of rationality, contrasting it with other useful notions in the neighbourhood. It is then shown that the target notion relies on first-person awareness of the unfolding of cognition. This is used to explain the kernel of truth in epistemic conservatism, the structure of defeasibility, and the root motive behind the widely accepted distinction between rational inference and trivial entailment.