Probabilistic models have started to replace classical logic as the standard reference paradigm in human deductive reasoning. Mental probability logic emphasizes general principles where human reasoning deviates from classical logic, but agrees with a probabilistic approach (like nonmonotonicity or the conditional event interpretation of conditionals). -/- This contribution consists of two parts. In the first part we discuss general features of reasoning systems including consequence relations, how uncertainty may enter argument forms, probability intervals, and probabilistic informativeness. These concepts are of (...) central importance for the psychological task analysis. In the second part we report new experimental data on the paradoxes of the material conditional, the probabilistic modus ponens, the complement task, and data on the probabilistic truth table task. The results of the experiments provide evidence for the hypothesis that people represent indicative conditionals by conditional probability assertions. (shrink)

We offer a particularist defense of conspiratorial thinking. We explore the possibility that the presence of a certain kind of evidence—what we call "fortuitous data"—lends rational credence to conspiratorial thinking. In developing our argument, we introduce conspiracy theories and motivate our particularist approach (§1). We then introduce and define fortuitous data (§2). Lastly, we locate an instance of fortuitous data in one real world conspiracy, the Watergate scandal (§3).

Conpiracy theories are widely deemed to be superstitious. Yet history appears to be littered with conspiracies successful and otherwise. (For this reason, "cock-up" theories cannot in general replace conspiracy theories, since in many cases the cock-ups are simply failed conspiracies.) Why then is it silly to suppose that historical events are sometimes due to conspiracy? The only argument available to this author is drawn from the work of the late Sir Karl Popper, who criticizes what he calls "the conspiracy theory (...) of society" in The Open Society and elsewhere. His critique of the conspiracy theory is indeed sound, but it is a theory no sane person maintains. Moreover, its falsehood is compatible with the prevalence of conspiracies. Nor do his arguments create any presumption against conspiracy theories of this or that. Thus the belief that it is superstitious to posit conspiracies is itself a superstition. The article concludes with some speculations as to why this superstition is so widely believed. (shrink)

Many millions of people hold conspiracy theories; they believe that powerful people have worked together in order to withhold the truth about some important practice or some terrible event. A recent example is the belief, widespread in some parts of the world, that the attacks of 9/11 were carried out not by Al Qaeda, but by Israel or the United States. Those who subscribe to conspiracy theories may create serious risks, including risks of violence, and the existence of such theories (...) raises significant challenges for policy and law. The first challenge is to understand the mechanisms by which conspiracy theories prosper; the second challenge is to understand how such theories might be undermined. Such theories typically spread as a result of identifiable cognitive blunders, operating in conjunction with informational and reputational influences. A distinctive feature of conspiracy theories is their self-sealing quality. Conspiracy theorists are not likely to be persuaded by an attempt to dispel their theories; they may even characterize that very attempt as further proof of the conspiracy. Because those who hold conspiracy theories typically suffer from a crippled epistemology, in accordance with which it is rational to hold such theories, the best response consists in cognitive infiltration of extremist groups. Various policy dilemmas, such as the question whether it is better for government to rebut conspiracy theories or to ignore them, are explored in this light. (shrink)

As the end of the Millennium approaches, conspiracy theories are increasing in number and popularity. In this short essay, I offer an analysis of conspiracy theories inspired by Hume's discussion of miracles. My first conclusion is that whereas Hume can argue that miracles are, by definition, explanations we are not warranted in believing, there is nothing analytic that will allow us to distinguish good from bad conspiracy theories. There is no a priori method for distinguishing warranted conspiracy theories (say, those (...) explaining Watergate) from those which are unwarranted (say, theories about extraterrestrials abducting humans). Nonetheless, there is a cluster of characteristics often shared by unwarranted conspiracy theories. An analysis of the alleged explanatory virtues of unwarranted conspiracies suggests some reasons for their current popularity, while at the same time providing grounds for their rejection. Finally, I discuss how conspiracy theories embody an anachronistic world-view that places the contemporary zeitgeist in a clearer light. (shrink)

A remarkable feature of the philosophical work on conspiracy theory theory has been that most philosophers agree there is nothing inherently problematic about conspiracy theories (AKA the thesis of particularism). Recent work, however, has challenged this consensus view, arguing that there really is something epistemically wrong with conspiracy theorising (AKA generalism). Are particularism and generalism incompatible? By looking at just how much particularists and generalists might have to give away to make their theoretical viewpoints compatible, I will argue that particularists (...) can accept many of the concerns that motivate generalism because generalism can never be about ‘all’ conspiracy theories without being either ahistorical or apolitical. In the end generalist critiques are best seen as useful guidelines or considerations for the appraising of particular conspiracy theories. (shrink)

Looking at the early work in the philosophy of conspiracy theory theory, I put in context the papers in this special issue on new work on conspiracy theory theory (itself the product of the 1st International Conference on the Philosophy of Conspiracy Theory held in February 2022), showing how this new generation of work not only grew out of, but is itself a novel extension of the first generation of philosophical interest in these things called ‘conspiracy theories’.

Critics of conspiracy theories often charge that such theories are implausible because conspiracies of the kind they allege tend to fail. Thus, according to these critics, conspiracy theories that have been around for a while would have been, in all likelihood, already exposed if they had been real. So, they reason, they probably are not. In this article, I maintain that the arguments in support of this view are unconvincing. I do so by examining a list of four sources recently (...) cited in support of the claim that conspiracies tend to fail. I pay special attention to two of these sources, an article by Brian Keeley, and, especially, an article by David Grimes, which is perhaps the single “best” article in support of the idea that conspiracies tend to fail. That is, it offers the most explicit and elaborate attempt to establish this view. Further, that article has garnered significant (uncritical) attention in the mainstream press. I argue that Grimes's argument does not succeed, that the common assertion that conspiracies tend to fail remains poorly supported, and that there are good reasons to think that at least some types of conspiracies do not tend to fail. (shrink)

This chapter presents probability logic as a rationality framework for human reasoning under uncertainty. Selected formal-normative aspects of probability logic are discussed in the light of experimental evidence. Specifically, probability logic is characterized as a generalization of bivalent truth-functional propositional logic (short “logic”), as being connexive, and as being nonmonotonic. The chapter discusses selected argument forms and associated uncertainty propagation rules. Throughout the chapter, the descriptive validity of probability logic is compared to logic, which was used as the gold standard (...) of reference for assessing the rationality of human reasoning in the 20th century. (shrink)

This position paper advocates combining formal epistemology and the new paradigm psychology of reasoning in the studies of conditionals and reasoning with uncertainty. The new paradigm psychology of reasoning is characterized by the use of probability theory as a rationality framework instead of classical logic, used by more traditional approaches to the psychology of reasoning. This paper presents a new interdisciplinary research program which involves both formal and experimental work. To illustrate the program, the paper discusses recent work on the (...) paradoxes of the material conditional, nonmonotonic reasoning, and Adams’ Thesis. It also identifies the issue of updating on conditionals as an area which seems to call for a combined formal and empirical approach. (shrink)

There is a long tradition in formal epistemology and in the psychology of reasoning to investigate indicative conditionals. In psychology, the propositional calculus was taken for granted to be the normative standard of reference. Experimental tasks, evaluation of the participants’ responses and psychological model building, were inspired by the semantics of the material conditional. Recent empirical work on indicative conditionals focuses on uncertainty. Consequently, the normative standard of reference has changed. I argue why neither logic nor standard probability theory provide (...) appropriate rationality norms for uncertain conditionals. I advocate coherence based probability logic as an appropriate framework for investigating uncertain conditionals. Detailed proofs of the probabilistic non-informativeness of a paradox of the material conditional illustrate the approach from a formal point of view. I survey selected data on human reasoning about uncertain conditionals which additionally support the plausibility of the approach from an empirical point of view. (shrink)

Belief in conspiracy theories is often taken to be a paradigm of epistemic irrationality. Yet, as I argue in the first half of this paper, standard criticisms of conspiracy theorising fail to demonstrate that the practice is invariably irrational. Perhaps for this reason, many scholars have taken a relatively charitable attitude toward conspiracy theorists and conspiracy theorising in recent years. Still, it would be a mistake to conclude from the defence of conspiracy theorising offered here that belief in conspiracy theories (...) is on an epistemic par with belief in other theories. I argue that a range of epistemic errors are pervasive among conspiracy theorists. First, the refusal of conspiracy theorists to accept the official account of some target event often seems to be due to the exercise of a probabilistic, and fallacious, extension ofmodus tollens. Additionally, conspiracy theorists tend to be inconsistent in their intellectual attention insofar as the effort they expend on uncovering the truth excludes attention to their own capacities for biased or otherwise erroneous reasoning. Finally, the scepticism with which conspiracy theorists tend to view common sources of information leaves little room for conspiracy theorists to attain positive warrant for their preferred explanations of target events. (shrink)

Vice epistemology is the philosophical study of the nature, identity, and epistemological significance of intellectual vices. Such vices include gullibility, dogmatism, prejudice, closed-mindedness, and negligence. These are intellectual character vices, that is, intellectual vices that are also character traits. I ask how the notion of an intellectual character vice should be understood, whether such vices exist, and how they might be epistemologically significant. The proposal is that intellectual character vices are intellectual character traits that impede effective and responsible inquiry. I (...) argue that situationist critiques of virtue epistemology pose no significant threat to this proposal. Studies by social psychologists of belief in conspiracy theories suggest that it is sometimes appropriate to explain questionable beliefs by reference to intellectual character vices. Neither ‘regulative’ nor ‘analytic’ epistemology has any good reason to question the epistemological significance of such vices. (shrink)

Nonmonotonic reasoning is often claimed to mimic human common sense reasoning. Only a few studies, though, have investigated this claim empirically. We report four experiments which investigate three rules of SYSTEMP, namely the AND, the LEFT LOGICAL EQUIVALENCE, and the OR rule. The actual inferences of the subjects are compared with the coherent normative upper and lower probability bounds derived from a non-infinitesimal probability semantics of SYSTEM P. We found a relatively good agreement of human reasoning and principles of nonmonotonic (...) reasoning. Contrary to the results reported in the ‘heuristics and biases’ tradition, the subjects committed relatively few upper bound violations (conjunction fallacies). (shrink)

We study probabilistically informative (weak) versions of transitivity by using suitable definitions of defaults and negated defaults in the setting of coherence and imprecise probabilities. We represent p-consistent sequences of defaults and/or negated defaults by g-coherent imprecise probability assessments on the respective sequences of conditional events. Moreover, we prove the coherent probability propagation rules for Weak Transitivity and the validity of selected inference patterns by proving p-entailment of the associated knowledge bases. Finally, we apply our results to study selected probabilistic (...) versions of classical categorical syllogisms and construct a new version of the square of opposition in terms of defaults and negated defaults. (shrink)

Orr and Dentith argue that a recurrent problem in much of the wider academic literature on conspiracy theories is either conceptual confusion or a refusal to put theory before practice. Orr and Dentith show that a naive empiricism pervades much of the social science literature when it comes to these things called ‘conspiracy theories’ which not only runs at odds with the philosophical literature but also the general tenor of the social sciences over the latter part of the 20th Century (...) and beyond. Orr and Dentith argue that central to these confusions or refusals is not just a lack of philosophical rigour when it comes to defining and presenting views, but an active disinterest in such conceptual work. (shrink)

The hexagon of opposition is an improvement of the square of opposition due to Robert Blanché. After a short presentation of the square and its various interpretations, we discuss two important problems related with the square: the problem of the I-corner and the problem of the O-corner. The meaning of the notion described by the I-corner does not correspond to the name used for it. In the case of the O-corner, the problem is not a wrong-name problem but a no-name (...) problem and it is not clear what is the intuitive notion corresponding to it. We explain then that the triangle of contrariety proposed by different people such as Vasiliev and Jespersen solves these problems, but that we don’t need to reject the square. It can be reconstructed from this triangle of contrariety, by considering a dual triangle of subcontrariety. This is the main idea of Blanché’s hexagon. We then give different examples of hexagons to show how this framework can be useful to conceptual analysis in many different fields such as economy, music, semiotics, identity theory, philosophy, metalogic and the metatheory of the hexagon itself. We finish by discussing the abstract structure of the hexagon and by showing how we can swing from sense to non-sense thinking with the hexagon. (shrink)

We are pleased to present this special issue of the journal History and Philosophy of Logic dedicated to the square of opposition.The square of opposition is a diagram and a theory of opposition re...

The paper first introduces a cube of opposition that associates the traditional square of opposition with the dual square obtained by Piaget’s reciprocation. It is then pointed out that Blanché’s extension of the square-of-opposition structure into an conceptual hexagonal structure always relies on an abstract tripartition. Considering quadripartitions leads to organize the 16 binary connectives into a regular tetrahedron. Lastly, the cube of opposition, once interpreted in modal terms, is shown to account for a recent generalization of formal concept analysis, (...) where noticeable hexagons are also laid bare. This generalization of formal concept analysis is motivated by a parallel with bipolar possibility theory. The latter, albeit graded, is indeed based on four graded set functions that can be organized in a similar structure. (shrink)