Sven Ove Hansson

Full meet contraction, that was devised by Carlos Alchourrón and David Makinson in the early 1980' s, has often been overlooked since it is not in itself a plausible contraction operator. However, it is a highly useful building-block in the construction of composite contraction operators. In particular, all plausible contraction operators can be reconstructed so that the outcome of contracting a belief set K by a sentence p is defined as K ∼ f, where ∼ is full meet contraction and f a sentential selector, i.e. a function to and from sentences. This paper investigates the logic of full meet contraction. Seven properties of this operation are presented that contribute to making it useful as a building-block: Full meet contraction is a purely logical operation. It retains finitebasedness of the belief set. It is the inclusion-maximal contraction that removes all sentences that can contribute to implying the input sentence. It is the inclusion-maximal contraction that removes all non-tautologous consequences of the input sentence. Almost all contractions can be reconstructed as full meet contraction. Full meet contraction allows for recovery of the input sentence. Full meet contraction provides a unified account of multiple and singleton contraction. La llamada full meet contraction, creada por Carlos Alchourrón y David Makinson en los comienzos de los ' 80, ha sido a menudo desestimada puesto que ella no constituye un operador de contracción plausible. De todas formas ella es altamente útil en la construcción de operadores de contracción compuestos. En particular, todos los operadores de contracción plausibles pueden ser reconstruidos de forma tal que la contracción de un conjunto de creencias K por una sentencia p sea definida como K ∼ f, donde ∼ es una full meet contraction y f un selector de sentencias, i.e., una función de sentencias a sentencias. En este trabajo investigamos la lógica de la full meet contraction. Se presentan siete propiedades de esta operación que contribuyen a hacerla útil como building-block: Full meet contraction es una operación puramente lógica. Ella retiene la finit- basednes del conjunto de creencias. Ella es la máxima-inclusiva de las contracciones que elimina todas las sentencias que pueden contribuir a implicar la input-sentence. Es la contracción maximal inclusiva que elimina todas las consecuencias no tautológicas de la input-sentence. Casi todas las contracciones pueden ser reconstruidas como full-meet contractions. Full meet contraction permite la recuperación de la input-sentence. Full meet contracción da cuenta en forma unificada de las contracciones múltiples y singulares

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

An agent can usually hold a very large number of beliefs. However, only a small part of these beliefs is used at a time. Efficient operations for belief change should affect the beliefs of the agent locally, that is, the changes should be performed only in the relevant part of the belief state. In this paper we define a local consequence operator that only considers the relevant part of a belief base. This operator is used to define local versions of the operations for belief change. Representation theorems are given for the local operators.

Several attempts have been made to transfer the concept of informed consent from medical and research ethics to dealing with affected groups in other areas such as engineering, land use planning, and business management. It is argued that these attempts are unsuccessful since the concept of informed consent is inadequate for situations in which groups of affected persons are dealt with collectively (rather than individually, as in clinical medicine). There are several reasons for this. The affected groups from which informed consent is sought cannot be identified with sufficient precision. Informed consent is associated with individual veto power, but it does not appear realistic to give veto power to all individuals who are affected for instance by an engineering project. Most importantly, the concept of informed consent puts focus on the public’s acceptance of ready-made proposals rather than on its participation in the decision-making process as a whole, which includes the development of alternatives for the decision. Therefore, the concept of informed consent is not applicable to a company’s relations with groups and collectives. It may, however, be applicable to a company’s relations with individual persons such as customers and employees.

Two of the major problems in AGM-style belief revision, namely the difficulties in accounting for iterated change and for Ramsey test conditionals, have satisfactory solutions in descriptor revision. In descriptor revision, the input is a metalinguistic sentence specifying the success condition of the operation. The choice mechanism selects one of the potential outcomes in which the success condition is satisfied. Iteration of this operation is unproblematic. Ramsey test conditionals can be introduced without giving rise to the paradoxical results that they generate in other systems. In addition to standard Ramsey test conditionals, a more general variant of epistemic conditionals is defined, representing statements of the form ”if the belief state is changed to satisfy condition A then it will satisfy condition B”. An axiomatic characterization of such descriptor conditionals is presented. It is related in intricate ways to the KLM postulates for cumulative reasoning.

An agent can usually hold a very large number of beliefs. However, only a small part of these beliefs is used at a time. Efficient operations for belief change should affect the beliefs of the agent locally, that is, the changes should be performed only in the relevant part of the belief state. In this paper we define a local consequence operator that only considers the relevant part of a belief base. This operator is used to define local versions of the operations for belief change. Representation theorems are given for the local operators.

Den moralfilosofiska traditionen har sina begränsningar. De frågor som stått i centrum för den moralfilosofiska diskussionen har ofta varit helt andra än de som människor i det praktiska livet har uppfattat som centrala moraliska problem. En viktig begränsning är att moralfilosofin, liksom beslutsteorin, nästan uteslutande har handlat om hur man hanterar välavgränsade problem där handlingsalternativen är givna. I det verkliga livet löser vi ofta moraliska problem genom att finna på nya handlingsalternativ, som inte fanns med från början.1 En annan begränsning är att moralfilosofin till allra största delen har handlat om situationer där konsekvensen av de olika handlingsalternativen är välkänd. I det praktiska livet är det annorlunda. Vi vet sällan med säkerhet vad som kommer att bli följden av de olika alternativ som vi väljer mellan. Man kan också uttrycka detta så att moralfilosofin i huvudsak rör sig i en tänkt deterministisk värld, där man inte behöver räkna med någon slump. Detta är aningen märkligt mot bakgrund av det oerhörda genomslag som sannolikhetstänkande och på senare år även kaos har fått inom andra vetenskapsområden. Det finns naturligtvis förklaringar till detta moralfilosofins kvardröjande i en äldre världsbild. Redan i det deterministiska fallet uppstår svårhanterliga problem som man gärna ger sin odelade uppmärksamhet. Dessutom finns det en särskild disciplin, beslutsteorin, som behandlar beslut under risk och osäkerhet. Man har i allmänhet tänkt sig ett slags arbetsfördelning, där problemen med risk och osäkerhet utelämnas i moralfilosofin för att i stället hanteras inom beslutsteorin med rena rationalitetsprinciper (dvs. utan att moraliska principer är inblandade). Enligt min mening är denna arbetsfördelning inte hållbar. Betrakta t ex osäkerheten om hur klimatet kommer att förändras med nuvarande utsläppstrender för växthusgaser. Denna osäkerhet ger upphov inte enbart till ett problem om rationellt beslutsfattande utan också till moraliska problem..

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.

Clear-cut cases of decision-making under risk (known probabilities) are unusual in real life. The gambler’s decisions at the roulette table are as close as we can get to this type of decision-making. In contrast, decision-making under uncertainty (unknown probabilities) can be exemplified by a decision whether to enter a jungle that may contain unknown dangers. Life is usually more like an expedition into an unknown jungle than a visit to the casino. Nevertheless, it is common in decision-supporting disciplines to proceed as if reasonably reliable probability estimates were available for all possible outcomes, i.e. as if the prevailing epistemic conditions were analogous to those of gambling at the roulette table. This mistake can be called the tuxedo fallacy . It is argued that traditional engineering practices such as safety factors and multiple safety barriers avoid this fallacy and that they therefore manage uncertainty better than probabilistic risk analysis (PRA). PRA is a useful tool, but it must be supplemented with other methods in order not to limit the analysis to dangers that can be assigned meaningful probability estimates.