Sven Ove Hansson

Generalizations of partial meet contraction are introduced that start out from the observation that only some of the logically closed subsets of the original belief set are at all viable as contraction outcomes. Belief contraction should proceed by selection among these viable options. Several contraction operators that are based on such selection mechanisms are introduced and then axiomatically characterized. These constructions are more general than the belief base approach. It is shown that partial meet contraction is exactly characterized by adding to one of these constructions the condition that all logically closed subsets of the belief set can be obtained as the outcome of a single (multiple) contraction. Examples are provided showing the counter-intuitive consequences of that condition, thus confirming the credibility of the proposed generalization of the AGM framework

The ideal world semantics of standard deontic logic identifies our obligations with how we would act in an ideal world. However, to act as if one lived in an ideal world is bad moral advice, associated with wishful thinking rather than well-considered moral deliberation. Ideal world semantics gives rise to implausible logical principles, and the metaphysical arguments that have been put forward in its favour turn out to be based on a too limited view of truth-functional representation. It is argued that ideal world semantics should be given up in favour of other, more plausible uses of possible worlds for modelling normative subject-matter.

Moral theory has mostly focused on idealized situations in which the morally relevant properties of human actions can be known beforehand. Here, a framework is proposed that is intended to sharpen moral intuitions and improve moral argumentation in problems involving risk and uncertainty. Guidelines are proposed for a systematic search of suitable future viewpoints for hypothetical retrospection. In hypothetical retrospection, a decision is evaluated under the assumption that one of the branches of possible future developments has materialized. This evaluation is based on the deliberator’s present values, and each decision is judged in relation to the information available when it was taken. The basic decision rule is to choose an alternative that comes out as morally acceptable (permissible) from all hypothetical retrospections.

A conceptual analysis of falsificationism is performed, in which the central falsificationist thesis is divided into several components. Furthermore, an empirical study of falsification in science is reported, based on the 70 scientific contributions that were published as articles in Nature in 2000. Only one of these articles conformed to the falsificationist recipe for successful science, namely the falsification of a hypothesis that is more accessible to falsification than to verification. It is argued that falsificationism relies on an incorrect view of the nature of scientific inquiry and that it is, therefore, not a tenable research methodology.

An experiment, in the standard scientific sense of the term, is a procedure in which some object of study is subjected to interventions that aim at obtaining a predictable outcome or at least predictable aspects of the outcome. The distinction between an experiment and a non-experimental observation is important since they are tailored to different epistemic needs. Experimentation has its origin in pre-scientific technological experiments that were undertaken in order to find the best technological means to achieve chosen ends. Important parts of the methodological arsenal of modern experimental science can be traced back to this pre-scientific, technological tradition. It is claimed that experimentation involves a unique combination of acting and observing, a combination whose unique epistemological properties have not yet been fully clarified.

Mainstream moral theories deal with situations in which the outcome of each possible action is well-determined and knowable. In order to make ethics relevant for problems of risk and uncertainty, moral theories have to be extended so that they cover actions whose outcomes are not determinable beforehand. One approach to this extension problem is to develop methods for appraising probabilistic combinations of outcomes. This approach is investigated and shown not to solve the problem. An alternative approach is then developed. Its starting-point is that everyone has a prima facie moral right not to be exposed to risk. However, this right can be overridden if the risk-exposure is part of an equitable system for risk-taking that works to the advantage of the individual risk-exposed person.

Mainstream risk analysis deviates in at least two important respects from the rationality ideal of mainstream economics. First, expected utility maximization is not applied in a consistent way. It is applied to endodoxastic uncertainty, i.e. the uncertainty (or risk) expressed in a risk assessment, but in many cases not to metadoxastic uncertainty, i.e. uncertainty about which of several competing assessments is correct. Instead, a common approach to metadoxastic uncertainty is to only take the most plausible assessment into account. This will typically lead to risk-prone deviations from risk-neutrality. Secondly, risks and benefits for different persons are added to form a total value of risk. Such calculations are used to support the view that one should accept being exposed to a risk if it brings greater benefits for others. This is in stark contrast to modern Paretian welfare economics, that refrains from interindividual comparisons and does not require people to accept a disadvantage because it brings a larger advantage for others. (Published Online July 11 2006).

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.