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.

By replacement is meant an operation that replaces one sentence by another in a belief set. Replacement can be used as a kind of Sheffer stroke for belief change, since contraction, revision, and expansion can all be defined in terms of it. Replacement can also be defined either in terms of contraction or in terms of revision. Close connections are shown to hold between axioms for replacement and axioms for contraction and revision. Partial meet replacement is axiomatically characterized. It is shown that this operation can have outcomes that are not obtainable through either partial meet contraction or partial meet revision.

Science is praxis relevant to the extent that it guides goal-directed action by telling us how to act in order to achieve the goals. Investigations aiming at high praxis relevance are performed in various disciplines under names such as clinical trials, evaluation research, intervention research and social experiments. In this contribution, the notion of (direct) praxis relevance is delineated, and it is distinguished from related properties of science such as those of being applied and being practically useful in a wider sense. Recommendations for the achievement of praxis relevance are offered in the form of five principles: the prerogative of direct experiments, minimized theory-induced uncertainty, multiple approximations, causal chain decomposition and successive improvements.

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. (Published Online July 31 2007).

Two recent defences of the recovery postulate for contraction of belief sets are analyzed. It is concluded that recovery is defensible as a by-product of a formalization that is idealized in the sense of being simplified for the sake of clarity. However, recovery does not seem to be a required feature of the doxastic behaviour of ideal (perfectly rational) agents. It is reasonable to expect that there should be epistemic residues (remnants of rejected beliefs), but not that these should always suffice to recover all the original beliefs if the discarded belief is reinstated.

This is a response to an article by Wade Allison in which he argues that we should accept drastically higher doses of ionizing radiation than what we currently do. He employs four arguments in defence of his position: comparisons with background radiation, the positive experiences of radiotherapy, the presence of biological defence mechanisms against radiation, and a concession by Swedish authorities that their approach to reindeer meat after the Chernobyl fallout was unnecessarily strict. It is shown that each of the four arguments is fallacious. In conclusion, the traditional weighing of risks against benefits in radiation protection is defended.