Hans Rott

Among the most important of Sten Lindström’s achievements in philosophy and logic is that he was the first researcher to realise that the theory of rational choice can be brought to bear in the domain of logic and reasoning. The new conception was that a sentence α is a consequence of a set of sentences Γ just in case α is true in all selected ("best", "most plausible") possible worlds in which all sentences in Γ are true (rather than in all possible worlds in which all sentences in Γ are true). And the selection of possible worlds should conform to the constraints on rational choices. Sten worked out this idea in stunning depth, detail and precision in his seminal paper "A semantic approach to nonmonotonic reasoning: Inference operations and choice." The paper was ready in draft form in April 1991 and presented in two talks later that year. It was included, in almost the same form, in the report series Uppsala Prints and Preprints in Philosophy in 1994, but it was never regularly published. The 2022 publication in Theoria seeks to compensate for this omission.

This article explores conditionals expressing that the antecedent makes a difference for the consequent. A ‘relevantised’ version of the Ramsey Test for conditionals is employed in the context of the classical theory of belief revision. The idea of this test is that the antecedent is relevant to the consequent in the following sense: a conditional is accepted just in case the consequent is accepted if the belief state is revised by the antecedent and the consequent fails to be accepted if the belief state is revised by the antecedent’s negation. The connective thus defined violates almost all of the traditional principles of conditional logic, but it obeys an interesting logic of its own. The article also gives the logic of an alternative version, the ‘Dependent Ramsey Test,’ according to which a conditional is accepted just in case the consequent is accepted if the belief state is revised by the antecedent and the consequent is rejected if the belief state is revised by the antecedent’s negation. This conditional is closely related to David Lewis’s counterfactual analysis of causation.

This note presents a very brief history of the observation that the probability of the material conditional A⊃B is in general different from, but cannot be less than, the conditional probability of B given A. The difference between the two probabilities is significant for the interpretation of conditionals and for the possibility of inductive probability. It can be quantitatively specified in so-called ‘excess laws’ for which Popper appears to have claimed priority. I argue that such a priority claim should be rejected and credit should instead be given, if to anyone, to Boole and Reichenbach instead.

The negation thesis concerning ignorance ("Nichtwissen") states that someone is ignorant about p if and only if she is does not know that p, or briefly, that ignorance is the negation of knowledge. We argue that there are no compelling arguments against the negation thesis. Even though, depending on the context of the conversation, the focus of an ascription of ignorance will be on one of the conditions for knowledge, all four types of ignorance are possible: ignorance due to falsity, ignorance due to lack of belief, ignorance due to lack of justification, and ignorance due to epistemic luck. Then we discuss the relevance of the distinction between known unknowns and unknown unknowns, and the surprising idea that every strong belief may be identified with an unknown unknown. A desire not to know can be present for a variety of reasons. It may be either symmetrical (not wanting to know whether p) or asymmetrical (not wanting to know that p if p should be true). We argue for the thesis that the desire not to know usually amounts to a desire to preserve the epistemic status quo. The potential applications of these distinctions to the alleged right not to know particularly in medical contexts are largely left open in this paper.

Wolfgang Spohn's theory of ranking functions is an elegant and powerful theory of the structure and dynamics of doxastic states. In two recent papers, Spohn has applied it to the analysis of conditionals, claiming to have presented a unified account of indicative and subjunctive (counterfactual) conditionals. I argue that his analysis fails to account for counterfactuals that refer to indirect causes. The strategy of taking the transitive closure that Spohn employs in the theory of causation is not available for counterfactuals. I have a close look at Spohn's treatment of the famous Oswald-Kennedy case in order to illustrate my points. I sketch an alternative view that seems to avoid the problems.

A theoretical term gets its meaning from a set of meaning-constitutive or 'analytic' sentences of the relevant theory. The meanings of theoretical terms may change when the theories change. After a discussion of Kant and Frege, I propose a broadly Quinean view of analyticity, without adopting Quine's meaning skepticism. A sentence of a given theory in a certain language is called analytic if revising the theory so that this sentence is lost entails the abandonment of the given linguistic (alternatively, of the given theoretical) framework. This solution to the problem of defining analyticity is rooted in intuitive judgements of the members of a linguistic community about the identity of languages or theories.

An idea going back to Plato’s Meno is that knowledge is stable. Recently, a seemingly stronger and more exciting thesis has been advanced, namely that rational belief is stable. I sketch two stability theories of knowledge and rational belief, and present an example intended to show that knowledge need not be stable and rational belief need not be stable either. The second claim does not follow from the first, even if we take knowledge to be a special kind of rational belief. ‘Stability’ is an ambiguous term that has an internally conditional structure.

This paper explores conditionals expressing that the antecedent makes a difference for the consequent. A 'relevantised' version of the Ramsey Test for conditionals is employed in the context of the classical theory of belief revision. The idea of this test is that the antecedent is relevant to the consequent in the following sense: a conditional is accepted just in case (i) the consequent is accepted if the belief state is revised by the antecedent and (ii) the consequent fails to be accepted if the belief state is revised by the antecedent's negation. The connective thus defined violates almost all of the traditional principles of conditional logic, but it obeys an interesting logic of its own. The paper also gives the logic of an alternative version, the `Dependent Ramsey Test', according to which a conditional is accepted just in case (i) the consequent is accepted if the belief state is revised by the antecedent and (ii) it is rejected (e.g., its negation is accepted) if the belief state is revised by the antecedent's negation. This conditional is closely related to David Lewis's counterfactual analysis of causation.

This paper is about the statics and dynamics of belief states that are represented by pairs consisting of an agent's credences (represented by a subjective probability measure) and her categorical beliefs (represented by a set of possible worlds). Regarding the static side, we argue that the latter proposition should be coherent with respect to the probability measure and that its probability should reach a certain threshold value. On the dynamic side, we advocate Jeffrey conditionalisation as the principal mode of changing one's belief state. This updating method fits the idea of the Lockean Thesis better than plain Bayesian conditionalisation, and it affords a flexible method for adding and withdrawing categorical beliefs. We show that it fails to satisfy the traditional principles of Inclusion and Preservation for belief revision and the principle of Recovery for belief withdrawals{, as well as the Levi and Harper identities. We take this to be a problem for the latter principles rather than for the idea of coherent belief change.

The contributions to the Special Issue on Multiple Belief Change, Iterated Belief Change and Preference Aggregation are divided into three parts. Four contributions are grouped under the heading "multiple belief change" (Part I, with authors M. Falappa, E. Fermé, G. Kern-Isberner, P. Peppas, M. Reis, and G. Simari), five contributions under the heading "iterated belief change" (Part II, with authors G. Bonanno, S.O. Hansson, A. Nayak, M. Orgun, R. Ramachandran, H. Rott, and E. Weydert). These papers do not only pick up the particular questions raised, but also extend and modify the framework of Alchourrón, Gärdenfors and Makinson. Part III deals with preference aggregation and consists of one contribution (by F. Herzberg and D. Eckert).

A number of seminal papers on the logic of belief change by Alchourrön, Gärden-fors, and Makinson have given rise to what is now known as the AGM paradigm. The present discussion note is a response to Neil Tennant's [1994], which aims at a critical appraisal of the AGM approach and the introduction of an alternative approach. We show that important parts of Tennants's critical remarks are based on misunderstandings or on lack of information. In the course of doing this, we attend to some central philosophical issues in the theory of belief change, such as the choice of a representation for belief states and the meaning of an idealized rational agent.

This paper is about the situation in which an author (writer or speaker) presents a deductively invalid argument, but the addressee aims at a charitable interpretation and has reason to assume that the author intends to present a valid argument. How can he go about interpreting the author’s reasoning as enthymematically valid? We suggest replacing the usual find-the-missing-premise approaches by an approach based on systematic efforts to ascribe a belief state to the author against the background of which the argument has to be evaluated. The suggested procedure includes rules for recording whether the author in fact accepts or denies the premises and the conclusion, as well as tests for enthymematic validity and strategies for revising belief state ascriptions. Different degrees of interpretive charity can be exercised. This is one reason why the interpretation or reconstruction of an enthymematic argument typically does not result in a unique outcome.

As part of the conference commemorating Theoria's 75th anniversary, a round table discussion on philosophy publishing was held in Bergendal, Sollentuna, Sweden, on 1 October 2010. Bengt Hansson was the chair, and the other participants were eight editors-in-chief of philosophy journals: Hans van Ditmarsch (Journal of Philosophical Logic), Pascal Engel (Dialectica), Sven Ove Hansson (Theoria), Vincent Hendricks (Synthese), Søren Holm (Journal of Medical Ethics), Pauline Jacobson (Linguistics and Philosophy), Anthonie Meijers (Philosophical Explorations), Henry S. Richardson (Ethics) and Hans Rott (Erkenntnis)

Since the early 1980s, logical theories of belief revision have offered formal methods for the transformation of knowledge bases or “corpora” of data and beliefs. Early models have dealt with unconditional acceptance and integration of potentially belief-contravening pieces of information into the existing corpus. More recently, models of “non-prioritized” revision were proposed that allow the agent rationally to refuse to accept the new information. This paper introduces a refined method for changing beliefs by specifying constraints on the relative plausibility of propositions. Like the earlier belief revision models, the method proposed is a qualitative one, in the sense that no numbers are needed in order to specify the posterior plausibility of the new information. We use reference beliefs in order to determine the degree of entrenchment of the newly accepted piece of information. We provide two kinds of semantics for this idea, give a logical characterization of the new model, study its relation with other operations of belief revision and contraction, and discuss its intuitive strengths and weaknesses.

According to the Lockean thesis, a proposition is believed just in case it is highly probable. While this thesis enjoys strong intuitive support, it is known to conflict with seemingly plausible logical constraints on our beliefs. One way out of this conflict is to make probability 1 a requirement for belief, but most have rejected this option for entailing what they see as an untenable skepticism. Recently, two new solutions to the conflict have been proposed that are alleged to be non-skeptical. We compare these proposals with each other and with the Lockean thesis, in particular with regard to the question of how much we gain by adopting any one of them instead of the probability 1 requirement, that is, of how likely it is that one believes more than the things one is fully certain of.

This paper reorganizes and further develops the theory of partial meet contraction which was introduced in a classic paper by Alchourron, Gardenfors, and Makinson. Our purpose is threefold. First, we put the theory in a broader perspective by decomposing it into two layers which can respectively be treated by the general theory of choice and preference and elementary model theory. Second, we reprove the two main representation theorems of AGM and present two more representation results for the finite case that "lie between" the former, thereby partially answering an open question of AGM. Our method of proof is uniform insofar as it uses only one form of "revealed preference", and it explains where and why the finiteness assumption is needed. Third, as an application, we explore the logic characterizing theory contractions in the finite case which are governed by the structure of simple and prioritized belief bases.

Der Band vereint aktuelle Beiträge zu den Themenschwerpunkten Fiktion, Wahrheit und Interpretation im Hinblick auf fiktionale literarische Texte. Im Einzelnen werden Fragen wie die folgenden diskutiert: In welchem Verhältnis stehen Literatur und Wahrheit? Welche Rolle spielen Intentionen für die Interpretation? Sind fiktionale Texte ausschließlich fiktional? Lässt sich die Sprechakttheorie für die Beschreibung der in fiktionalen literarischen Texten enthaltenen Sätze fruchtbar machen? Warum nehmen wir Anteil an fiktionaler Literatur, obwohl wir wissen, dass die beschriebenen Personen und Ereignisse nicht real sind? Die Beiträger nehmen diese Problemfelder aus einer interdisziplinären Warte zwischen Literaturtheorie und analytischer Philosophie in den Blick.

This paper presents a number of apparent anomalies in rational choice scenarios, and their translation into the logic of everyday reasoning. Three classes of examples that have been discussed in the context of probabilistic choice since the 1960s (by Debreu, Tversky and others) are analyzed in a non-probabilistic setting. It is shown how they can at the same time be regarded as logical problems that concern the drawing of defeasible inferences from a given information base. I argue that initial appearances notwithstanding, these cases should not be classed as instances of irrationality in choice or reasoning. One way of explaining away their apparent oddity is to view certain aspects of these examples as making particular options salient. The decision problems in point can then be solved by ‘picking’ these options, although they could not have been ‘chosen’ in a principled way, due to ties or incomparabilities with alternative options.