Sven Ove Hansson

Specified meet contraction is the operation defined by the identity where ∼ is full meet contraction and f is a sentential selector, a function from sentences to sentences. With suitable conditions on the sentential selector, specified meet contraction coincides with the partial meet contractions that yield a finite-based contraction outcome if the original belief set is finite-based. In terms of cognitive realism, specified meet contraction has an advantage over partial meet contraction in that the selection mechanism operates on sentences rather than on temporary infinite structures (remainders) that are cognitively inaccessible. Specified meet contraction provides a versatile framework in which other types of contraction, such as severe withdrawal and base-generated contraction, can be expressed with suitably chosen properties of the sentential selector.

Real-life decision-making often begins with a disorderly decision problem that has to be clarified and systematized before a decision can be made. This is the process of decision structuring that has largely been ignored both in decision theory and applied decision analysis. In this contribution, ten major components of decision structuring are identified, namely the determination of its scope, subdivision, agency, timing, options, control ascriptions, framing, horizon, criteria and restructuring. Four of these components, namely the scope, subdivision, options, and horizon of a decision, are subjected to a more detailed analysis.

In order to avoid the paradoxes of standard deontic logic, we have to give up the semantic construction that identifies obligatory status with presence in all elements of a subset of the set of possible worlds. It is proposed that deontic logic should instead be based on a preference relation, according to the principle that whatever is better than something permitted is itself permitted. Close connections hold between the logical properties of a preference relation and those of the deontic logics that are derived from it in this way. The paradoxes of SDL can be avoided with this construction, but it is still an open question what type of preference relation is best suited to be used as a basis for deontic logic.

The purpose of this presentation is to introduce both the concept of risk and the precautionary principle, that is a major policy principle in present-day risk management. Since risk has been the subject of many misconceptions I will do this in large part by criticizing seven views on risk that I believe to have caused considerable confusion both among scientists and policy-makers. But before looking at the seven myths of risk, let us begin with the basic issue of defining “risk”. The word “risk” often refers, rather vaguely, to situations in which it is possible but not certain that some undesirable event will occur. In addition, the word has several more specialized meanings. Let me illustrate this by making a few statements about the single most important preventable health hazard in non-starving countries. First: “Lung cancer is one of the major risks that affect smokers.” Here, we use “risk” in the following sense: (1) risk = an unwanted event which may or may not occur. 1 (15).

The AGM (Alchourrón-Gärdenfors-Makinson) model of belief change is extended to cover changes on sets of beliefs that are not closed under logical consequence (belief bases). Three major types of change operations, namely contraction, internal revision, and external revision are axiomatically characterized, and their interrelations are studied. In external revision, the Levi identity is reversed in the sense that one first adds the new belief to the belief base, and afterwards contracts its negation. It is argued that external revision represents an intuitively plausible way of revising one's beliefs. Since it typically involves the temporary acceptance of an inconsistent set of beliefs, it can only be used in belief representations that distinguish between different inconsistent sets of belief