Theory change is a central concern in contemporary epistemology and philosophy of science. In this paper, we investigate the relationships between two ongoing research programs providing formal treatments of theory change: the (post-Popperian) approach to verisimilitude and the AGM theory of belief change. We show that appropriately construed accounts emerging from those two lines of epistemological research do yield convergences relative to a specified kind of theories, here labeled “conjunctive”. In this domain, a set of plausible conditions are identified which (...) demonstrably capture the verisimilitudinarian effectiveness of AGM belief change, i.e., its effectiveness in tracking truth approximation. We conclude by indicating some further developments and open issues arising from our results. (shrink)

In this paper, we address the problem of truth approximation through theory change, asking whether revising our theories by newly acquired data leads us closer to the truth about a given domain. More particularly, we focus on “nomic conjunctive theories”, i.e., theories expressed as conjunctions of logically independent statements concerning the physical or, more generally, nomic possibilities and impossibilities of the domain under inquiry. We define both a comparative and a quantitative notion of the verisimilitude of such theories, and identify (...) suitable conditions concerning the (partial) correctness of acquired data, under which revising our theories by data leads us closer to “the nomic truth”, construed as the target of scientific inquiry. We conclude by indicating some further developments, generalizations, and open issues arising from our results. (shrink)

I argue that it is rational for a person to believe the conjunction of her beliefs. This involves responding to the Lottery and Preface Paradoxes. In addition, I suggest that in normal circumstances, what it is to believe a conjunction just is to believe its conjuncts.

Some theories of rational belief assume that beliefs should be closed under conjunction. I motivate the rejection of the conjunction closure, and point out that the consequences of this rejection are not as severe as it is usually thought. An often raised objection is that without the conjunction closure people are unable to reason. I outline an approach in which we can – in usual cases – reason using conjunctions without accepting the closure in its whole (...) generality. This solution is based on the notion of confidence levels, which can be defined using probabilities. Moreover, on this approach, reasoning has a scalable computational complexity adaptable to cognitive abilities of both rationally bounded and perfectly rational agents. I perform a simulation to assess its error rate, and compare it to reasoning with conjunction closure. (shrink)

If people believe that some property is true of all members of a class such as sofas, then they should also believe that the same property is true of all members of a conjunctively defined subset of that class such as uncomfortable handmade sofas. A series of experiments demonstrated a failure to observe this constraint, leading to what is termed the inverse conjunction fallacy. Not only did people often express a belief in the more general statement but not in (...) the more specific, but also when they accepted both beliefs, they were inclined to give greater confidence to the more general. It is argued that this effect underlies a number of other demonstrations of fallacious reasoning, particularly in category-based induction. Alternative accounts of the phenomenon are evaluated, and it is concluded that the effect is best interpreted in terms of intensional reasoning [Tversky, A., & Kahneman, D.. Extensional versus intuitive reasoning: the conjunction fallacy in probability judgment. Psychological Review, 90, 293-315.]. (shrink)

I argue that any account of imagination should satisfy the following three desiderata. First, imaginations induce actions only in conjunction with beliefs about the environment of the imagining subject. Second, there is a continuum between imaginations and beliefs. Recognizing this continuum is crucial to explain the phenomenon of imaginative immersion. Third, the mental states that relate to imaginations in the way that desires relate to beliefs are a special kind of desire, namely desires to make true (...) in fiction. These desires to make true in fiction do not differ from regular desires in kind, but only in content. I argue for these three desiderata in turn by critically discussing several recent accounts of imagination. (shrink)

It is widely believed that one should not become more confident that all swans are white and all lions are brave simply by observing white swans. Irrelevant conjunction or “tacking” of a theory onto another is often thought problematic for Bayesianism, especially given the ratio measure of confirmation considered here. It is recalled that the irrelevant conjunct is not confirmed at all. Using the ratio measure, the irrelevant conjunction is confirmed to the same degree as the relevant conjunct, (...) which, it is argued, is ideal: the irrelevant conjunct is irrelevant. Because the past’s really having been as it now appears to have been is an irrelevant conjunct, present evidence confirms theories about past events only insofar as irrelevant conjunctions are confirmed. Hence the ideal of not confirming irrelevant conjunctions would imply that historical claims are not confirmed. Confirmation measures partially realizing that ideal make the confirmation of historical claims by present evidence depend strongly on the (presumably subjective) degree of belief in the irrelevant conjunct. The unusually good behavior of the ratio measure has a bearing on the problem of measure sensitivity. For non-statistical hypotheses, Bayes’ theorem yields a fractional linear transformation in the prior probability, not a linear rescaling, so even the ratio measure arguably does not aptly measure confirmation in such cases. (shrink)

The aim of this paper is to argue that what I call the simple theory of introspection can be extended to account for our introspective knowledge of what we believe as well as what we consciously experience. In section one, I present the simple theory of introspection and motivate the extension from experience to belief. In section two, I argue that extending the simple theory provides a solution to Moore’s paradox by explaining why believing Moorean conjunctions always involves some degree (...) of irrationality. In section three, I argue that it also solves the puzzle of transparency by explaining why it’s rational to answer the question whether one believes that p by answering the question whether p. Finally, in section four, I defend the simple theory against objections by arguing that self-knowledge constitutes an ideal of rationality. (shrink)

Ordinary usage supports both a relatively strong belief requirement on intention and a tight conceptual connection between intention and intentional action. More specifically, it speaks in favor both of the view that "S intends to A" entails "S believes that he (probably) will A" and of the thesis that "S intentionally A-ed" entails "S intended to A." So, at least, proponents of these ideas often claim or assume, and with appreciable justification. The conjunction of these two ideas, however, has (...) some highly counterintuitive implications. This suggests that a certain skepticism about the coherence of ordinary usage of "intention" may be salutary. Fortunately, the skeptic need not abandon the quest for understanding. Much can be gleaned from a careful investigation of the functions attributed to intention in the literature. In this paper, I argue that the capacity of intention to do the work that the literature assigns it does not depend upon intentional A-ing's entailing intending to A, nor upon there being a strong belief constraint on intention, nor even a certain relatively weak belief constraint. I also develop an account of the features of intention in virtue of which it is capable of doing this work. This account provides the core of an adequate conception of intention. Toward the end of the paper, I briefly motivate acceptance of a modest belief requirement on non-functional grounds. (shrink)

Is there a Moore ’s paradox in desire? I give a normative explanation of the epistemic irrationality, and hence absurdity, of Moorean belief that builds on Green and Williams’ normative account of absurdity. This explains why Moorean beliefs are normally irrational and thus absurd, while some Moorean beliefs are absurd without being irrational. Then I defend constructing a Moorean desire as the syntactic counterpart of a Moorean belief and distinguish it from a ‘Frankfurt’ conjunction of desires. Next (...) I discuss putative examples of rational and irrational desires, suggesting that there are norms of rational desire. Then I examine David Wall’s groundbreaking argument that Moorean desires are always unreasonable. Next I show against this that there are rational as well as irrational Moorean desires. Those that are irrational are also absurd, although there seem to be absurd desires that are not irrational. I conclude that certain norms of rational desire should be rejected. (shrink)

When a belief has been influenced, in part or whole, by factors that, by the believer's own lights, do not bear on the truth of the believed proposition, we can say that the belief has been, in a sense, arbitrarily formed. Can such beliefs ever be rational? It might seem obvious that they can't. After all, belief, supposedly, “aims at the truth.” But many epistemologists have come to think that certain kinds of arbitrary beliefs can, indeed, be rational. (...) In this paper, I want to do two things. First, I want to show that the claim that arbitrary beliefs can be rational is inconsistent with the conjunction of two other attractive claims: one saying that rationality requires a certain kind of epistemic immodesty, and one saying that rationality forbids certain kinds of self-ascriptions of epistemic luck. Second, I want to evaluate different ways one might respond to this inconsistent triad. I won't defend any response in particular, but I'll draw out some notable costs and benefits of each response, which may help shed light on the question of whether arbitrary beliefs can be rational. (shrink)

Human agents happen to judge that a conjunction of two terms is more probable than one of the terms, in contradiction with the rules of classical probabilities—this is the conjunction fallacy. One of the most discussed accounts of this fallacy is currently the quantum-like explanation, which relies on models exploiting the mathematics of quantum mechanics. The aim of this paper is to investigate the empirical adequacy of major quantum-like models which represent beliefs with quantum states. We first (...) argue that they can be tested in three different ways, in a question order effect configuration which is different from the traditional conjunction fallacy experiment. We then carry out our proposed experiment, with varied methodologies from experimental economics. The experimental results we get are at odds with the predictions of the quantum-like models. This strongly suggests that this quantum-like account of the conjunction fallacy fails. Future possible research paths are discussed. (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)

Starting from the sixties of the past century theory change has become a main concern of philosophy of science. Two of the best known formal accounts of theory change are the post-Popperian theories of verisimilitude (PPV for short) and the AGM theory of belief change (AGM for short). In this paper, we will investigate the conceptual relations between PPV and AGM and, in particular, we will ask whether the AGM rules for theory change are effective means for approaching the truth, (...) i.e., for achieving the cognitive aim of science pointed out by PPV. First, the key ideas of PPV and AGM and their application to a particular kind of propositional theories - the so called "conjunctive propositions" - will be illustrated. Afterwards, we will prove that, as far as conjunctive propositions are concerned, AGM belief change is an effective tool for approaching the truth. (shrink)

Many philosophers agree with Socrates that it is not possible to perform an akratic action consciously and freely. They take this view because they assimilate the internal irrationality of such a performance to the internal irrationality of drawing a theoretical conclusion which contadicts one's premisses. This article develops some arguments against that assimilation. The extreme cost of theoretical self-contradiction is forming the belief both that something is so and that it is not so. This is impossible for anyone who understands (...) what he is doing, and the impossibility can be explained: nothing could conceivably make such a conjunction of beliefs true. But the conjunction of a value-judgement judgment and an action that gets against it is different. Although it too is internally irrational, there is no property like truth which the value-judgement and his action ought both to possess, but cannot both possess. This article proposes a different model for akratic action, which might serve as a basis for disagreement with Socrates' view of it. (shrink)

According to the so-called Lockean thesis, a rational agent believes a proposition just in case its probability is sufficiently high, i.e., greater than some suitably fixed threshold. The Preface paradox is usually taken to show that the Lockean thesis is untenable, if one also assumes that rational agents should believe the conjunction of their own beliefs: high probability and rational belief are in a sense incompatible. In this paper, we show that this is not the case in general. (...) More precisely, we consider two methods of computing how probable must each of a series of propositions be in order to rationally believe their conjunction under the Lockean thesis. The price one has to pay for the proposed solutions to the paradox is what we call “quasi-dogmatism”: the view that a rational agent should believe only those propositions which are “nearly certain” in a suitably defined sense. (shrink)

Ernest Sosa's A Virtue Epistemology, Vol. I is arguably the single-most important monograph to be published in analytic epistemology in the last ten years. Sosa, the first in the field to employ the notion of intellectual virtue – in his ground-breaking ‘The Raft and the Pyramid’– is the leading proponent of reliabilist versions of virtue epistemology. In A Virtue Epistemology, he deftly defends an externalist account of animal knowledge as apt belief, argues for a distinction between animal and reflective knowledge, (...) contends that rational intuition is an intellectual virtue ; and offers responses to dream scepticism, the problem of the criterion and the value problem. Nearly all of these arguments are new, albeit consistent with Sosa's earlier work; that is, consistent with two notable exceptions. First, c ontra Sosa's ‘Replies’ in Ernest Sosa and His Critics, A Virtue Epistemology explicitly contends that safety is not required for animal knowledge. Second, unlike Sosa's Knowledge in Perspective, which arguably construes the intellectual virtues as merely instrumentally valuable, A Virtue Epistemology explicitly contends that the intellectual virtues are instrumentally and constitutively valuable. Best read in conjunction with the above monographs and Epistemic Justification, A Virtue Epistemology is mandatory reading for epistemologists and graduate students in the field. It will rightly set the standard for debates in analytic epistemology for years to come.I will summarize and raise objections to two key conclusions that are unique to A Virtue Epistemology: the ‘kaleidoscope-perceiver’ has animal knowledge but lacks reflective knowledge; unlike the k-perceiver, the ordinary perceiver has reflective knowledge. My objections …. (shrink)

According to Fumerton in his "How Does Perception Justify Belief?", it is misleading or wrong to say that perception is a source of justification for beliefs about the external world. Moreover, reliability does not have an essential role to play here either. I agree, and I explain why in section 1, using novel considerations about evil demon scenarios in which we are radically deceived. According to Fumerton, when it comes to how sensations or experiences supply justification, they do not (...) do so on their own, and instead only do so only in conjunction with support for background beliefs about how the sensations or experiences are best explained. Here I disagree. In section 2, I first clarify the question of whether sensations or experiences provide justification on their own. I then respond to Fumerton’s arguments that use considerations about concept-possession and about how to close possible gaps between experience and truth. In section 3, I develop my main concern about his positive view, where that concern also brings out some of the merits of the view that experiences do justify beliefs about the external world on their own. (shrink)

We define infinitary extensions to classical epistemic logic systems, and add also a common belief modality, axiomatized in a finitary, fixed-point manner. In the infinitary K system, common belief turns to be provably equivalent to the conjunction of all the finite levels of mutual belief. In contrast, in the infinitary monotonic system, common belief implies every transfinite level of mutual belief but is never implied by it. We conclude that the fixed-point notion of common belief is more powerful than (...) the iterative notion of common belief. (shrink)

In this paper, I offer reasons to conclude that either belief impermissivism or credal impermissivism is false. That is to say, I argue against the conjunction of belief impermissivism and credal impermissivism. I defend this conclusion in three ways. First, I show what I take to be an implausible consequence of holding that for any rational credence in p, there is only one correlating rational belief-attitude toward p, given a body of evidence. Second, I provide thought experiments designed to (...) support the intuition that there are at least a few credences in some cases for which more than one belief-attitude is rationally permissible. Third, I provide one possible theoretical grounding for my position by appeal to Jamesian values. (shrink)

Sidney Shoemaker has given an influential explanation of the absurdity of Moore-paradoxical belief in terms of conscious belief. Here I offer a novel account of the absurdity of Moore-paradoxical assertion in terms of an interlocutor’s fully conscious beliefs. This account starts with an original argument for the principle that fully conscious belief collects over conjunction. The argument is premised on the synchronic unity of consciousness and the transparency of belief.

Defenders of doxastic voluntarism accept that we can voluntarily commit ourselves to propositions, including belief-contravening propositions. Thus, defenders of doxastic voluntarism allow that we can choose to believe propositions that are negatively implicated by our evidence. In this paper it is argued that the conjunction of epistemic deontology and doxastic voluntarism as it applies to ordinary cases of belief-contravening propositional commitments is incompatible with evidentialism. In this paper ED and DV will be assumed and this negative result will be (...) used to suggest that voluntary belief-contravening commitments are not themselves beliefs and that these sorts of commitments are not governed by evidentialism. So, the apparent incompatibility of the package views noted above can be resolved without ceding evidentialism with respect to beliefs. (shrink)

Papers collected in this volume were originally presented at a symposium held at the University of Pennsylvania in December, 1968 and revised in the light of discussion at the symposium for publication. The contributors hold different views about the role played by induction in theories of knowledge and rational belief but many of the papers are conciliatory, reflecting no doubt a good deal of helpful communication at the symposium. For example, Frederic Schick's clearly written and informative lead article considers subjectivist, (...) empiricist, and pragmatist theories of rational belief, arguing that they are compatible theories relevant to different types of issues. Marshall Swain follows with an article which presents a general framework within which rules of rational acceptance can be constructed. An exchange between Isaac Levi and Richard Jeffrey shows that advocates of theories of acceptance and theories of partial belief may be defending complementary and not mutually exclusive theories. In the remaining three essays Henry Kyburg Jr., Gilbert Harman, and Keith Lehrer defend their own distinctive views about the nature of inductive inference and rational belief. Kyburg traces difficulties in some theories to the acceptance of the principle of conjunction which he rejects. Harman and Lehrer both see the relation of inductive inference to explanation as crucial to understanding the former and they develop theories along different lines which make use of this relation. A long and useful bibliography was prepared for the symposium by Ralph L. Slaght and revised for publication in the volume.--R. H. K. (shrink)

When a Christian refers to the future full realization of the kingdom of God in an afterlife, it is typically assumed that she is expressing beliefs about the existence and activity of God in conjunction with supernatural beliefs about an otherworldly realm and the possibility of one’s personal survival after bodily death. In other words, the religious language is interpreted in a realist fashion and the religious person here is construed as a religious believer. A corollary of (...) this widely-held realist view is the assumption that if one were to conclude that there is no good reason to believe the asserted claims—for example, no reason to believe that we may survive our bodily deaths in a heavenly realm—then there is no reason to engage in the use of such religious language and the practices which accompany it. I argue that this assumption is false—that there is a meaningful way to use such language in a religious context that does not rest on believing supernatural claims. Against the backdrop of Kant’s discussion of a kingdom of ends understood as a regulative ideal, I argue that religious discourse about the kingdom of God being brought to fruition may be reinterpreted as a useful fiction to draw our attention to and engage our emotions with a distinctive ideal of restorative justice. Though I and others have previously offered fictionalist accounts of language about God, I extend the view here to some religious language about the afterlife. (shrink)

In 2004, I explained the absurdity of Moore-paradoxical belief via the syllogism (Williams 2004): (1) All circumstances that justify me in believing that p are circumstances that tend to make me believe that p. (2) All circumstances that tend to make me believe that p are circumstances that justify me in believing that I believe that p. (3) All circumstances that justify me in believing that p are circumstances that justify me in believing that I believe that p. I then (...) took (3) to mean (EP) Whatever justifies me in believing that p justifies me in believing that I believe that p.1 Now suppose that I am justified in believing anything of the omissive Mooreparadoxical form: (Om) p and I do not believe that p. Then I am justified in believing the first conjunct. So by (EP) I am justified in believing that I believe that p. But since I am also justified in believing the second conjunct, I am justified in believing that I do not believe that p. I claimed that this is impossible, because anything that justifies me in believing that something is the case renders me unjustified in believing that it is not the case. This syllogism is plausible from an externalist view of justification, according to which circumstances such as seeming to see rain under normal perceptual conditions, justify me in believing that it is raining. In support of (1), if my apparent perceptions of rain are reliably connected with rain, so as to justify me in thinking that it is raining, they also tend to make me believe that it is raining. In support of (2), my apparent perceptions of rain are also reliably connected with my coming to believe that it is raining. However, Anthony Brueckner (2006) argues that (1) and (EP) are both false once justification is thought of evidentially. Against (EP), he claims that my evidence that p is not evidence that I believe that p unless I possess the evidence, in the sense that I believe it and were I to believe that p on its basis. (shrink)

Behaviorally, children’s explicit theory of mind (ToM) proceeds in a progression of mental-state understandings: developmentally, children demonstrate accurate explicit desire-reasoning before accurate explicit belief-reasoning. Given its robust and cross-cultural nature, we hypothesize this progression may be paced in part by maturation/specialization of the brain. Neuroimaging research demonstrates that the right temporoparietal junction (TPJ) becomes increasingly selective for ToM reasoning as children age, and as their ToM improves. But this research has narrowly focused on beliefs or on undifferentiated mental-states. A (...) recent ERP study in children included a critical contrast to desire-reasoning, and demonstrated that right posterior potentials differentiated belief-reasoning from desire-reasoning. Taken together, the literature suggests that children’s desire-belief progression may be paced by specialization of the right TPJ for belief-reasoning specifically, beyond desire-reasoning. In the present study, we tested this hypothesis directly by examining children’s belief- and desire-reasoning using functional near-infrared spectroscopy in conjunction with structural magnetic resonance imaging to pinpoint brain activation in the right TPJ. Results showed greatest activation in the right TPJ for belief-reasoning, beyond desire-reasoning, and beyond non-mental reasoning (control). Findings replicate and critically extend prior ERP results, and provide clear evidence for a specific neural mechanism underlying children’s progression from understanding desires to understanding beliefs. (shrink)

I am justified in believing that my lottery ticket—call it t1—will not win, on statistical grounds. Those grounds apply equally to any other ticket, so I am justified in believing of any other ticket ti (let i take values from 2 to 1000000) that it will not win. I am not, however, justified in believing the giant conjunctive proposition that t1 will not win & t2 will not win & . . . & t1,000,000 will not win. On the contrary, (...) I am justified in believing that some ticket will win, hence that one of those conjuncts is false. Suggested solution: justified belief is not closed under conjunction. It does not follow from the fact that I am justified in believing p and justified in believing q that I am justified in believing p & q. (shrink)

This paper discusses a set of observations, many of which are novel, concerning differences between the adjectival modals _certain_ and _possible_ and their adverbial counterparts _certainly_ and _possibly_. It argues that the observations can be derived from a standard interpretation of _certain_/_certainly_ as universal and _possible_/_possibly_ as existential quantifiers over possible worlds, in conjunction with the hypothesis that the adjectives quantify over knowledge and the adverbs quantify over belief. The claims on which the argument relies include the following: (i) (...) knowledge implies belief, (ii) agents have epistemic access to their belief, (iii) relevance is closed under speakers’ belief, and (iv) commitment is pragmatically inconsistent with explicit denial of belief. (shrink)

Iterated admissibility embodies a minimal criterion of rationality in interactions. The epistemic characterization of this solution has been actively investigated in recent times: it has been shown that strategies surviving \ rounds of iterated admissibility may be identified as those that are obtained under a condition called rationality and m assumption of rationality in complete lexicographic type structures. On the other hand, it has been shown that its limit condition, with an infinity assumption of rationality ), might not be satisfied (...) by any state in the epistemic structure, if the class of types is complete and the types are continuous. In this paper we analyze the problem in a different framework. We redefine the notion of type as well as the epistemic notion of assumption. These new definitions are sufficient for the characterization of iterated admissibility as the class of strategies that indeed satisfy \. One of the key methodological innovations in our approach involves defining a new notion of generic types and employing these in conjunction with Cohen’s technique of forcing. (shrink)

This paper is about guessing: how people respond to a question when they aren’t certain of the answer. Guesses show surprising and systematic patterns that the most obvious theories don’t explain. We argue that these patterns reveal that people aim to optimize a tradeoff between accuracy and informativity when forming their guess. After spelling out our theory, we use it to argue that guessing plays a central role in our cognitive lives. In particular, our account of guessing yields new theories (...) of belief, assertion, and the conjunction fallacy—the psychological finding that people sometimes rank a conjunction as more probable than one of its conjuncts. More generally, we suggest that guessing helps explain how boundedly rational agents like us navigate a complex, uncertain world. (shrink)

This paper aims to defend scientific realism against two versions of agnostic empiricism: a naive agnostic position, which suggests that the only rational option is to remain agnostic as to the truth of theoretical assertions, and van Fraassen's more sophisticated agnostic empiricism - which may be called "Hypercritical Empiricism". It first argues that given semantic realism, naive agnostic empiricism cannot be maintained: there is no relevant epistemic difference between theoretical assertions and observational ones. It then focuses on van Fraassen's more (...) sophisticated alternative to scientific realism and suggests that an attitude towards science which involves less than aiming at theoretical truth and believing in theories would be, in some concrete respect that empiricists should recognize, worse off than the recommended realist attitude. To this end, the paper develops the so-called conjunction argument into a diachronic argument for scientific realism. (shrink)

We argue that giving up on the closure of rational belief under conjunction comes with a substantial price. Either rational belief is closed under conjunction, or else the epistemology of belief has a serious diachronic deficit over and above the synchronic failures of conjunctive closure. The argument for this, which can be viewed as a sequel to the preface paradox, is called the ‘review paradox'; it is presented in four distinct, but closely related versions.

This chapter focuses on one of the common fallacies in Western philosophy called the conjunction fallacy. It discusses a case of Linda who was deeply concerned with issues of discrimination and social justice and also participated in antinuclear demonstrations. The chapter applies the concept the present fallacy to the Linda Problem by using a Venn diagram. When one needs to determine the relative probability of different scenarios, one way to prevent himself/herself from making the conjunction fallacy is to (...) determine whether any of the options is a subset of any other. If so, he/she can conclude that the subset option is not more probable. This rule works because a specific event can never be more likely than a general event that encompasses the specific event. The chapter explains why people are so frequently drawn in by the conjunction fallacy. (shrink)

Information generally comes from less than fully reliable sources. Rationality, it seems, requires that one take source reliability into account when reasoning on the basis of such information. Recently, Bovens and Hartmann (2003) proposed an account of the conjunction fallacy based on this idea. They show that, when statements in conjunction fallacy scenarios are perceived as coming from such sources, probability theory prescribes that the “fallacy” be committed in certain situations. Here, the empirical validity of their model was (...) assessed. The model predicts that statements added to standard conjunction problems will change the incidence of the fallacy. It also predicts that statements from reliable sources should yield an increase in fallacy rates (relative to unreliable sources). Neither the former (Experiment 1) nor the latter prediction (Experiment 3) was confirmed, although Experiment 2 showed that people can derive source reliability estimates from the likelihood of statements in a manner consistent with the tested model. In line with the experimental results, model fits and sensitivity analyses also provided very little evidence in favor of the model. This suggests that Bovens and Hartmann’s present model fails to explain fully people’s judgements in standard conjunction fallacy tasks. (shrink)

In this paper I defend the claim that justification is closed under conjunction, and confront its most alarming consequence — that one can have justification for believing propositions that are unlikely to be true, given one's evidence.