Hans Rott

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.

This paper compares three accounts of what can be inferred from a knowledge base that contains conditionals: Lehmann and Magidor’s Rational Entailment; Pearl’s System Z, later extended and refined in collaboration with Goldszmidt; and the present author’s Nonmonotonic conditional logic for belief revision. We show that although the ideas motivating these systems are strikingly different, they are formally equivalent. An explanation of the surprising parallel is offered in terms of the interpretation of conditionals in the context of nonmonotonic reasoning and belief revision. Finally, some common problems with the equivalent systems are outlined, as well as some problems in assessing these problems which indicate that a general definition of dependence between the items in a knowledge base is needed.

In this paper we study changes of beliefs in a ranking-theoretic setting using non-extremal implausibility thresholds for belief. We represent implausibilities as ranks and introduce natural rank changes subject to a minimal change criterion. We show that many of the traditional AGM postulates for revision and contraction are preserved, except for the postulate of Preservation which is invalid. The diagnosis for belief contraction is similar, but not exactly the same. We demonstrate that the one-shot versions of both revision and contraction can be represented as revisions based on semiorders, but in two subtly different ways. We provide sets of postulates that are sound and complete in the sense that they allow us to prove representation theorems. We show that, and explain why, the classical duality between revision and contraction, as exhibited by the Levi and Harper identities, is partly broken by threshold-based belief changes. We also study the logic of iterated threshold-based revision and contraction. The traditional Darwiche-Pearl postulates for iterated revision continue to hold, as well as two additional postulates that characterize ranking-based revision as a restricted `improvement' operator. We investigate the dual notion of iterated threshold-based belief contraction and provide a new set of postulates for it, characterizing contraction as a restricted 'degrading' operator.

According to Otto Neurath, the practice of science consists in a large undertaking of setting up and maintaining systems of statements: In unified science we try ... to create a consistent system of protocol statements and nonprotocol statements . When a new statement is presented to us we compare it with the system at our disposal and check whether the new statement is in contradiction with the system or not. If the new statement is in contradiction with the system, we can discard this statement as unusable , for example, the statement: ‘In Africa lions sing only in major chords’ ; however, one can also ‘accept’ the statement and change the system accordingly so that it remains consistent if this statement is added. The statement may then be called ‘true’

Ein theoretischer Begriff erhält seine Bedeutung aus einer Reihe von bedeutungskonstitutiven oder "analytischen" Sätzen der betreffenden Theorie. Die Bedeutungen der theoretischen Begriffe können sich ändern, wenn sich die Theorien ändern. Nach einer Diskussion von Kant und Frege schlage ich eine weitgehend quineanische Interpretation von Analytizität vor, ohne jedoch die Quine'sche Bedeutungsskepsis zu übernehmen. Ein Satz einer bestimmten Theorie in einer bestimmten Sprache wird analytisch genannt, wenn die Revision der Theorie, so dass dieser Satz verloren geht, die Aufgabe des gegebenen sprachlichen (oder alternativ: des gegebenen theoretischen) Rahmens mit sich bringt. Diese Lösung des Problems der Definition von Analytizität gründet auf den intuitiven Urteilen der Mitglieder einer Sprachgemeinschaft über die Identität von Sprachen oder Theorien.

Theories of belief and meaning have long occupied philosophers. Typically, there is a correlation between the meaning of a sentence that is uttered and the content of the attitude that the speaker thereby conveys. This is also why a sentence can be used to specify content in an attribution of the attitude to the speaker. From the perspective of a theory of semantic content, there is a level of description where mental states and sentences can be said to share a content or meaning. But there is a contrary view gaining currency, claiming that belief and meaning have to be kept apart conceptually, theoretically, and methodologically. Thus it could be that meaning is an internal or private notion that can be accounted for purely linguistically (or even non-intentionally altogether), while the same may not be true of belief. The volume brings together researchers from various areas in philosophy, psychology, and linguistics to address these questions. The tradition of logical positivism, sometimes thought of as having been a passing phase in twentieth-century philosophy, has as a matter of record remained a vibrant force. But it has shifted from broadside critiques of other systems of thought into a deeper study of how the structure of logic and language impact human behavior and psychological conditioning. Among the contributors to this international symposium are Michael Esfeld, Wolfram Hisses, Max Kolbel, Isaac Levi, Diego Marconi, James McGilvary, Olaf Muller, Paul Peitroski and Norbert Hornstein, Sebastian Rodl, and Alberto Voltolini.

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.

According to Otto Neurath, the practice of science consists in a large undertaking of setting up and maintaining systems of statements: In unified science we try... to create a consistent system of protocol statements and nonprotocol statements. When a new statement is presented to us we compare it with the system at our disposal and check whether the new statement is in contradiction with the system or not. If the new statement is in contradiction with the system, we can discard this statement as unusable, for example, the statement: ‘In Africa lions sing only in major chords’ ; however, one can also ‘accept’ the statement and change the system accordingly so that it remains consistent if this statement is added. The statement may then be called ‘true’.

Die Philosophie wurde von so unterschiedlichen Philosophen wie Wolff und Russell als Moglichkeitswissenschaft bezeichnet. Doch erwiesen sich die modalen Konzepte von Moglichkeit und Notwendigkeit als sperrig und vieldeutig, und ihr Verhaltnis zum Wirklichkeitsbegriff bleibt problematisch. Die vorliegende Sammlung beleuchtet die Metaphysik und Logik von Moglichkeit und Wirklichkeit aufs Neue und betrachtet sie aus unterschiedlichsten Perspektiven jenseits der Dichotomie von analytischer und kontinentaler Philosophie. Die Philosophiegeschichte (von der griechischen Antike bis zu David Lewis) kommt ebenso zu Wort wie die Semantik moglicher Welten; Logik, Mathematik und Computerwissenschaft ebenso wie Literatur und Neue Medien; Formen des wissenschaftlichen ebenso wie des fiktionalen Diskurses. Philosophy has been called the science of the possible by philosophers as diverse as Christian Wolff and Bertrand Russell. The modal concepts of possibility and necessity, however, have proved to be ambiguous and recalcitrant to analysis, and their relation to the concept of reality have remained problematic up to the present day. Transcending the worn-out dichotomy between analytic and continental philosophy, this collection of papers takes a fresh look at the metaphysics and logic of possibility and reality, and illuminates them from a great variety of perspectives. Topics include the history of philosophy (from Greek antiquity to David Lewis) as well as the semantics of possible worlds; logic, mathematics and computer science as well as literature and the new media; forms of scientific as well as fictional discourse."

Today there is a wealth of fascinating studies of connexive logical systems. But sometimes it looks as if connexive logic is still in search of a convincing interpretation that explains in intuitive terms _why_ the connexive principles should be valid. In this paper I argue that difference-making conditionals as presented in Rott (_Review of Symbolic Logic_ 15, 2022) offer one principled way of interpreting connexive principles. From a philosophical point of view, the idea of difference-making demands full, unrestricted connexivity, because neither logical truths nor contradictions or other absurdities can ever ‘make a difference’ (i.e., be relevantly connected) to anything. However, difference-making conditionals have so far been only partially connexive. I show how the existing analysis of difference-making conditionals can be reshaped to obtain full connexivity. The classical AGM belief revision model is replaced by a conceivability-limited revision model that serves as the semantic base for the analysis. The key point of the latter is that the agent should never accept any absurdities.

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.

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.

The development of science does not proceed as a monotonous addition of information. A superior successor theory often contradicts its predecessor. The question as to what the logical relationship is between such theories, insofar as the transition from one to the other embodies continuity and progress, is the subject of this book. Proceeding from a discussion of intertheory reductions, the author proves that theories revision models from philosophical logic are fruitful for questions of scientific theory. Formal analyses of conditionals, autoepistemic inferences, intertheoretical explanations and idealizations are carried out, as well as applications to the Kepler-Newton case and the case of the ideal gas law and van der Waals's law.

The book addresses the questions how literature can convey knowledge and how literary meaning can arise in the face of the fact that fictional texts waive the usual claim to truth. Based on the interdisciplinary cooperation of literary scholars and analytic philosophers, the present anthology attempts a) to analyze the possibility and conditions of gaining knowledge through literature, and b) to apply, in a fruitful way, philosophical theories of meaning and interpretation to the constitution of meaning within the language of literature. The project is guided by the hypothesis that the cognitive function of literature cannot be understood without such fundamental modelings of the complex interaction of meaning, truth and knowledge.

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.

This is a survey paper. Contents: 1 Introduction ― 2 Preliminary remarks on information, truth and mind - 2.1 Remarks on information and truth - 2.2 Some clues from the philosophy of mind - 2.3 Functionalism as applied to belief revision - 2.4 Filling in the parameters ― 3 Belief change = revision + reflection - 3.1 Foundationalism - 3.2 Coherentism ― 4 Inference operations for simple change operations: three examples - 4.1 Example 1: flat data bases - 4.2 Example 2: up-sets in prioritized data bases - 4.3 Example 3: maximal-consistent sets in prioritized data bases ― 5 Representing coherentist belief change by operations on prioritized data bases - 5.1 Moderate revision - 5.2 Revision by comparison ― 6 A very brief history of belief revision - 6.1 The 1980s: AGM's classical model - 6.2 The 1990s: iteration - 6.3 The 2000s: merging ― 7 Conclusion