Group Beliefs: Studies on the Nature and Logic of Collective Doxastic Attitudes

The present doctoral dissertation studies the nature and logic of collective
doxastic attitudes, or what is referred to in ordinary language as "group
beliefs". Beliefs and other intentional attitudes are attributed to groups and
collections of people, and such attributions are used to explain and predict
the actions of groups. The dissertation develops an understanding of group
beliefs as voluntarily adopted views or acceptances rather than as ordinary
beliefs. Such an understanding can provide new answers to questions concerning
collective knowledge and justification of group beliefs, and it allows
developing modal logics with collective doxastic and epistemic notions.
The dissertation consists of six articles. The first three are philosophical
studies concerned with the nature of collective doxastic attitudes. The last
three articles, which are written jointly with Sara Negri, are logical studies
concerned with the logic of collective doxastic attitudes. Here is a short
review of the articles.

Among the former, the first one concerns the question whether group
beliefs are beliefs or acceptances. The second one discusses the possibility
of group knowledge, and the third one justification of group beliefs. Among
the latter, the first concerns one prerequisite for developing a proof theory
for modal logics in general, including doxastic and epistemic logics. The
last two present sequent calculus systems for logics that express properties
of two types of collective attitudes, distributed knowledge and group beliefs,
respectively.

In 'Group beliefs and the distinction between belief and acceptance', I
study the existing literature on group beliefs. There are two notions of group
beliefs: summative group beliefs, which are reducible to individual beliefs,
and non-summative, which are not reducible to individual beliefs but are
based on what the group members decide to take as the group's view. I use
the distinction between belief and acceptance to argue that non-summative
group beliefs are acceptances rather than ordinary beliefs. In the article, I
attempt to clarify the discussion by making the distinction between belief and
acceptance more precise than it had previously been made. The suggestion
is to define acceptances as voluntary doxastic states, in contrast to beliefs,
which are usually understood to be involuntary.

In `On the possibility of group knowledge without belief', I consider the
possibility of attributing knowledge to groups in spite of the conclusion of
the previous article that group beliefs might not be beliefs. This requires
a modification of standard epistemological theories that see knowledge as
belief satisfying certain conditions. The modification is plausible if we see
the distinction between belief and acceptance as a refinement of our ordinary language concept of belief. I also argue that the voluntariness of acceptance
suggests that its justification should be taken to require reasons for the accepted
view, whereas this may not be required for justification of belief.

In `On dialectical justification of group beliefs', I pursue the idea of the
previous article that voluntariness of group belief, and of acceptance more
generally, has consequences concerning the epistemic justification of such
doxastic states. I argue that it is plausible to require reasons for voluntary
acceptances whereas the epistemic assessment of involuntary beliefs may be
understood purely externalistically. I concentrate on dialectical theories of
justification and argue that the justification of group beliefs could be understood
dialectically.

In `Does the deduction theorem fail for modal logic?', we study the recent
claims according to which the deduction theorem fails for modal logics. The
deduction theorem states a property that is necessary for developing sequent
calculus systems for modal logics, including doxastic and epistemic logics.
We show that the deduction theorem holds when a correct formulation of
the inference rules and an appropriate understanding of logical consequence
are given.

In `Proof theory for distributed knowledge', we develop a cut-free Gentzen-type
sequent calculus for a multi-agent epistemic logic that is extended by
an operator for distributed knowledge. Something is distributed knowledge
within a group if and only if it is entailed by the totality of the knowledge
of the individuals belonging to the group. By interpreting the knowledge
modalities as belief (or acceptance) operators, the system can be used for reasoning about certain summative collective doxastic attitudes, such as shared
and distributed beliefs.

In `Reasoning about collectively accepted group beliefs', we extend the
methods of the previous paper to logics that concern non-summative group
beliefs. The proof-theoretical methods apply to the basic logic and to extensions
concerned with the aggregation of individual acceptances into a group
view. It turns out that care must be taken in defining the modalities in a
way that does not lead to inconsistent group beliefs in situations such as the
discursive dilemma in which there is a majority both for a conclusion and
premisses entailing the negation of the conclusion.