Sven Ove Hansson

Five charges against the precautionary principle

We defend the precautionary principle against five common charges, namely that it is ill-defined, absolutist, and a value judgement, increases risk-taking, and marginalizes science. We argue, first, that the precautionary principle is, in principle, no more vague or ill-defined than other decision principles and like them it can be made precise through elaboration and practice. Second, the precautionary principle need not be absolutist in the way that has been claimed. A way to avoid this is through combining the precautionary principle with a specification of the degree of scientific evidence required to trigger precaution, and/or with some version of the de minimis rule. Third, the precautionary principle does not lead to increased risk-taking, unless the framing is too narrow, and then the same problem applies to other decision rules as well. Fourth, the precautionary principle is indeed value-based, but only to the same extent as other decision rules. Fifth and last, the precautionary principle is not unscientific other than in the weak sense of not being exclusively based on science. In that sense all decision rules are unscientific.

Belief contraction without recovery

The postulate of recovery is commonly regarded to be the intuitively least compelling of the six basic Gärdenfors postulates for belief contraction. We replace recovery by the seemingly much weaker postulate of core-retainment, which ensures that if x is excluded from K when p is contracted, then x plays some role for the fact that K implies p. Surprisingly enough, core-retainment together with four of the other Gärdenfors postulates implies recovery for logically closed belief sets. Reasonable contraction operators without recovery do not seem to be possible for such sets. Instead, however, they can be obtained for non-closed belief bases. Some results on partial meet contractions on belief bases are given, including an axiomatic characterization and a non-vacuous extension of the AGM closure condition.

PHILOSOPHICAL PROBLEMS IN COST BENEFIT ANALYSIS

Cost–benefit analysis (CBA) is much more philosophically interesting than has in general been recognized. Since it is the only well-developed form of applied consequentialism, it is a testing-ground for consequentialism and for the counterfactual analysis that it requires. Ten classes of philosophical problems that affect the practical performance of cost–benefit analysis are investigated: topic selection, dependence on the decision perspective, dangers of super synopticism and undue centralization, prediction problems, the indeterminateness of our control over future decisions, the need to exclude certain consequences for moral reasons, bias in the delimitation of consequences, incommensurability of consequences, difficulties in defending the essential requirement of transferability across contexts, and the normatively questionable but equally essential assumption of interpersonal compensability.

A Survey of non-Prioritized Belief Revision

This paper summarizes and systematizes recent and ongoing work on non-prioritized belief change, i.e., belief revision in which the new information has no special priority due to its novelty.

Reversing the Levi identity

The AGM (Alchourrón-GÄrdenfors-Makinson) model of belief change is extended to cover changes on sets of beliefs that arenot 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 onefirst 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 ones 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.

A survey of multiple contractions

The AGM theory of belief contraction is extended tomultiple contraction, i.e. to contraction by a set of sentences rather than by a single sentence. There are two major variants: Inpackage contraction all the sentences must be removed from the belief set, whereas inchoice contraction it is sufficient that at least one of them is removed. Constructions of both types of multiple contraction are offered and axiomatically characterized. Neither package nor choice contraction can in general be reduced to contractions by single sentences; in the finite case choice contraction allows for reduction.

Decision-Making Under Great Uncertainty

This article is an attempt at a systematic account of decision making under greater uncertainty than what traditional, mathematically oriented decision theory can cope with. Four components of great uncertainty are distinguished: (1) the identity of the options is not well determined (uncertainty of demarcation) ; (2) the consequences of at least some option are unknown (uncertainty of consequences); (3) it is not clear whether information obtained from others, such as experts, can be relied on (uncertainty of reliance); and (4) the values relevant for the decision are not determined with sufficient precision (uncertainty of values). Some possible strategy types are proposed for each of these components. Decisions related to environmental issues are used to illustrate the proposals.This article is an attempt at a systematic account of decision making under greater uncertainty than what traditional, mathematically oriented decision theory can cope with. Four components of grea ...

Ethical Criteria of Risk Acceptance

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.

AGM 25 Years : Twenty-Five Years of Research in Belief Change

The 1985 paper by Carlos Alchourrón (1931–1996), Peter Gärdenfors, and David Makinson (AGM), “On the Logic of Theory Change: Partial Meet Contraction and Revision Functions” was the starting-point of a large and rapidly growing literature that employs formal models in the investigation of changes in belief states and databases. In this review, the first twenty-five years of this development are summarized. The topics covered include equivalent characterizations of AGM operations, extended representations of the belief states, change operators not included in the original framework, iterated change, applications of the model, its connections with other formal frameworks, computatibility of AGM operations, and criticism of the model.

Risk: objective or subjective, facts or values

Perhaps the most fundamental divide in risk research is that between proponents of two contradictory concepts of risk. Some take risk as objectively given and determined by physical facts, whereas others see risk as a social construction that is independent of physical facts. These two views are scrutinized, and it is concluded that neither is tenable. Risk is both fact‐laden and value‐laden, and it contains both objective and subjective components. It is argued that both the objectivist and the subjectivist view of risk are failed attempts to rid a complex concept of much of its complexity. The real challenge is to identify the various types of factual and valuational components inherent in statements about risk and to understand how they are combined. The two oversimplifications both stand in the way of a more sophisticated analysis of risk.