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**Naturalizing Epistemic Norms**

Interdisciplinary seminar (logic, mathematics, philosophy, psychology) co-organized by Joëlle Proust and Paul Egré.

The meeting will take place in the seminar room of Pavillon Jardin at Institut Jean-Nicod, ENS, 29, rue d'Ulm 75005 Paris.

Program

**June 27**, from 2:30 to 4:30, 29 Rue d'Ulm, __CRI Room__.

**Isabelle Drouet** (University of Paris 4)

"Causal reasoning, causal probabilities, and conceptions of causation"

Abstract :

The present paper deals with the tools that can be used to represent causation and to reason about it and, specifically, with their diversity. It focuses on so-called “causal probabilities”—that is, probabilities of effects given one of their causes—and critically surveys a recent paper in which Joyce (2010) argues that the values of these probabilities do not depend on one’s conception of causation. I first establish a stronger independence claim: I show that the very definition of causal probabilities is independent of one’s conception of causation. Second, I investigate whether causal probabilities indeed take the same values under their different possible definitions.

**May 29**, from 2 to 4:30 **Kevin Kelly **(Carnegie Mellon University)

"Propositional Reasoning that Tracks Probabilistic Reasoning"

Abstract:

According to the familiar Bayesian story, one has degrees of belief and one revises them in light of new propositional information by conditioning.

According to qualitative theories of belief revision, one has propositional beliefs that one revises in light of new propositional information. Of course, propositional reasoning will always be coarser than full Bayesian reasoning, but one would hope at least that the former could somehow correspond to or aptly represent the latter.

Traditionally, that correspondence has been understood in terms of acceptance: a rule that associates propositional belief states with probabilistic belief states. For example, the Lockean acceptance rule accepts all propositions whose probabilities exceed a given threshold. That rule occasions the familiar lottery paradox (Kyburg 1961). We will show that it also falls prey to new and more stubborn paradoxes when conditional probabilities are taken into account. We propose an alternative approach to acceptance that avoids all of the paradoxes and that, furthermore, is guaranteed to track Bayesian conditioning, in the sense that acceptance followed by propositional belief revision always yields exactly the same result as Bayesian conditioning followed by acceptance. The proposal combines an odds-based acceptance rule proposed originally by Levi (1996) with a non-AGM belief revision method proposed originally by Shoham (1987). We also show that the familiar AGM approach to belief revision (Harper 1975 and Alchourrón, Gärdenfors, and Makinson 1985) cannot be realized in a sensible way by any uncertain acceptance rule that tracks Bayesian conditioning in the sense just described.

**May 15th**, from 2 to 4:30,** Seth Yalcin** (UC Berkeley)

"Bayesian expressivism".

Abstract :

I develop a conception of expressivism according to which it is chiefly a pragmatic thesis about some fragment of discourse, one imposing certain constraints on semantics. The first half of the paper uses credal expressivism about the language of probability as a stalking-horse for this purpose. The second half turns to the question of how one might frame an analogous form of expressivism about the language of deontic modality. Here I offer a preliminary comparison of two expressivist lines. The first, expectation expressivism, looks again to Bayesian modelling for inspiration: it glosses deontically modal language as characteristically serving to express decision-theoretic expectation (expected utility). The second, plan expressivism, develops the idea (due to Gibbard 2003) that this language serves to express ‘plan-laden’ states of belief. In the process of comparing the views, I show how to incorporate Gibbard’s modelling ideas into a compositional semantics for attitudes and modals, filling a lacuna in the account. I close with the question whether and how plan expressivism might be developed with expectation-like structure.

**March 20**, from 2:30 to 4:30 pm,

Uncertainty and de Finetti’s three-valued logic, by **Jean Baratgin **(Université Paris 8, Saint-Denis) & Institut Jean Nicod (ENS, Paris)

Abstract:

The new paradigm in the psychology of reasoning adopts a Bayesian, or probabilistic, model to study human reasoning. This approach is supported by two findings:

- most people judge the probability of the indicative conditional, P(if A then C), to be the conditional probability, P(C|A), as implied by the Ramsey test.

- the existence of a so-called defective truth table in which people judge that if A then C is (i) true when A holds and C holds, (ii) false when A holds and C does not hold, and (iii) neither true nor false when A does not hold.

Our presentation focuses on this second point. Contrary to the traditional binary approach based on truth functional logic, with truth-values of truth and falsity, a third value that represents uncertainty is introduced in the new paradigm. Various three-valued truth table systems are available in the formal literature, including one proposed by de Finetti. We examine their descriptive adequacy, considering the usual connectives, and in particular the conditional. Within this framework the so-called defective truth table becomes an explainable and coherent response. Our main result is that the three-valued de Finetti’s logic (and only this one) shows a very good descriptive adequacy when uncertainty is introduced as a third truth-value.

**February 20**, 2013, from 2:30 to 4:30

**Paul Egré (**Institut Jean-Nicod) will present his joint work with **Vincent de Gardelle **(LPP) and **David Ripley **(Melbourne, UConn.)

"Vagueness and order effects: evidence for enhanced contrast in a task

of color categorization".

Abstract :

This paper proposes an experimental investigation of the use of vague predicates in dynamic sorites. We present the results of two studies in which subjects had to categorize colored squares at the borderline between two color categories (Green vs. Blue, Yellow vs. Orange). Our main aim was to probe for hysteresis in the ordered transitions between the respective colors, namely for the longer persistence of the initial category. Our main finding is a robust phenomenon of negative hysteresis or enhanced contrast, present in two diff erent tasks, a comparative task involving two color names, and a yes/no task involving a single color name. We propose an explanation of this e ffect in terms of the strict-tolerant framework of P. Cobreros, P.Egré, D. Ripley, and R. van Rooij (2012), "Tolerant, classical, strict", The Journal of Philosophical Logic, pp. 1-39, in which borderline cases are characterized in a dual manner in terms of overlap between tolerant extensions, and underlap between strict extensions.The framework, more generally, relies on two notions of assertion, whose relevance will be questioned from a broader epistemological perspective.

**Wednesday January 23**, 2013, from 3 to 5 pm,

**Dr Helen De Cruz** (Radcliffe Humanities Oxford and Leuven University)

"The epistemic significance of common consent".

Abstract

Philosophers have long focused on individual reasoning and experience as the main and sometimes even exclusive proper grounds for belief. In this picture of human reasoning, relying on common consent as a guideline to forming true beliefs seems like an awful strategy. Even in experimental psychology, the dominant paradigm (Asch-type experiments) pits consensus against truth. However, recent work in social epistemology prompts us to reassess common consent. According to social epistemology, the opinions of others constitute a source of knowledge, for instance, taking into account the opinion of a dissenting epistemic peer can be a valuable way of "coping with our own infirmities" (Christensen). This paper aims to assess the epistemic significance of common consent by looking at in the context of recent social epistemology, reviewing recent arguments from common consent by Zagzebski and Kelly. These arguments outline conditions under which deferring to majority opinion can be rational. I then survey how empirical findings in social psychology can be interpreted in the light of these normative frameworks. Finally, I examine theoretical models of cultural transmission in the light of the evidential value of common consent.

**Wednesday October 31**, from 3 to 5 pm,

in the seminar room of Pavillon Jardin at Institut Jean-Nicod.

**Igor Douven** (University of Groningen)

"Conditionals and Closure"

Abstract

It has long been held that high conditional degree of belief in an indicative conditional's consequent given its antecedent is necessary and sufficient for the acceptability of that conditional. Recently, it has been argued, both on theoretical and on empirical grounds, that the notion of evidential support plays a crucial role in the acceptability of indicative conditionals, next to that of high conditional degree of belief. It is still an open question under which principles acceptability is closed if we adopt this proposal. The present paper makes a beginning with answering that question.