Raul Hakli

TWO KINDS OF WE-REASONING

People sometimes think in terms of ‘we’ referring to a group they belong to. When making decisions, they frame the decision problem as: ‘What should we do?’ instead of ‘What should I do?’. We study one particular approach to such ‘we-reasoning’, economist Michael Bacharachs theory of ‘team reasoning’, and relate it to philosopher Raimo Tuomelas distinction between ‘I-mode’ reasoning and ‘we-mode’ reasoning. We argue that these theories complement each other: Tuomelas philosophical theory provides a conceptual framework augmenting Bacharachs theory, and Bacharachs mathematical results support Tuomelas view on the irreducibility of the we-mode to the I-mode. We-mode reasoning can explain some kinds of human cooperative behaviour left unexplained by standard game theory. Standard game theory is not well-equipped to deal with we-mode reasoning but it can be extended by the methods developed by Bacharach. However, we argue that both standard game theory and Bacharachs theory require more attention to the information-sharing stages that precede actual decision making, and we describe a stage-based model of we-reasoning.

Group beliefs and the distinction between belief and acceptance

Group beliefs, or collective doxastic states, are states analogous to beliefs but attributed to groups instead of individuals. In this paper, existing views on the nature of certain types of group beliefs, non-summative group beliefs, are critically examined. Some authors state that they are beliefs, others say that they are not beliefs but acceptances. It is here argued that the distinction between belief and acceptance is not as clear-cut as usually assumed. A common view is that the main difference between the two notions is that beliefs are based solely on evidence, whereas acceptances are affected by pragmatic goals. It is argued that this will not distinguish beliefs from acceptances, because both attitudes can be affected by both evidence on the one hand and goals on the other. It is suggested that the possibility to voluntarily acquire, abandon, or otherwise directly affect the attitude should be taken as the property that distinguishes acceptances from other doxastic states. The question of the nature of group beliefs can then be partially answered by considering whether these states can be taken to be voluntary or not. It has sometimes been claimed that group beliefs are not voluntary for the group but only for the individual group members. It is here argued that non-summative group beliefs should be understood as being voluntary for the group and should thus be classified as acceptances. Whether they should also be regarded as proper beliefs depends on whether the distinction is taken to be dichotomous or not.

Does the deduction theorem fail for modal logic

Various sources in the literature claim that the deduction theorem does not hold for normal modal or epistemic logic, whereas others present versions of the deduction theorem for several normal modal systems. It is shown here that the apparent problem arises from an objectionable notion of derivability from assumptions in an axiomatic system. When a traditional Hilbert-type system of axiomatic logic is generalized into a system for derivations from assumptions, the necessitation rule has to be modified in a way that restricts its use to cases in which the premiss does not depend on assumptions. This restriction is entirely analogous to the restriction of the rule of universal generalization of first-order logic. A necessitation rule with this restriction permits a proof of the deduction theorem in its usual formulation. Other suggestions presented in the literature to deal with the problem are reviewed, and the present solution is argued to be preferable to the other alternatives. A contraction- and cut-free sequent calculus equivalent to the Hilbert system for basic modal logic shows the standard failure argument untenable by proving the underivability of

Implementing a Declarative String Query Language with String Restructuring

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Design and implementation of a string database query language

from A.

Accommodative Belief Revision

A proof-theoretical treatment of collectively accepted group beliefs is presented through a multi-agent sequent system for an axiomatization of the logic of acceptance. The system is based on a labelled sequent calculus for propositional multi-agent epistemic logic with labels that correspond to possible worlds and a notation for internalized accessibility relations between worlds. The system is contraction- and cut-free. Extensions of the basic system are considered, in particular with rules that allow the possibility of operative members or legislators. Completeness with respect to the underlying Kripke semantics follows from a general direct and uniform argument for labelled sequent calculi extended with mathematical rules for frame properties. As an example of the use of the calculus we present an analysis of the discursive dilemma.

Adding string processing capabilities to data management systems

We describe the design and implementation of a declarative database query language for manipulating character strings. The language can be used to create logical predicates expressing structural properties of strings and relations between several strings. The predicates can be used to query strings in databases, and by leaving variables uninstantiated, also to generate new strings not contained in the database. A full working system was implemented as an extension of an object-oriented database management system and its query language. The declarative expressions are evaluated by first performing a compilation transforming them to nondeterministic finite state automata and then by simulating these automata using a depth-first search engine. The system checks the safety of each string-manipulation query in advance to preclude infinite ones. This safety checking provides also a compile-time loop-checking mechanism for the search engine, improving its eficiency.

Attitudinal Change in Elderly Citizens Toward Social Robots: The Role of Personality Traits and Beliefs About Robot Functionality.

The proof theory of multi-agent epistemic logic extended with operators for distributed knowledge is studied. A proposition A is distributed knowledge within a group G if A follows from the totality of what the individual members of G know. There are known axiomatizations for epistemic logics with the distributed knowledge operator, but apparently no cut-free proof system for such logics has yet been presented. A Gentzen-style contraction-free sequent calculus system for propositional epistemic logic with operators for distributed knowledge is given, and a cut-elimination theorem for the system is proved. Examples of reasoning about distributed knowledge that use the calculus are given.