Propositions and same-saying: introduction

Philosophers often talk about the things we say, or believe, or think, or mean. The things are often called ??propositions??. A proposition is what one believes, or thinks, or means when one believes, thinks, or means something. Talk about propositions is ubiquitous when philosophers turn their gaze to language, meaning and thought. But what are propositions? Is there a single class of things that serve as the objects of belief, the bearers of truth, and the meanings of utterances? How do our utterances express propositions? Under what conditions do two speakers say the same thing, and what (if anything) does this tell us about the nature of propositions? There is no consensus on these questions??or even on whether propositions should be treated as things at all. During the second Propositions and Same-Saying workshop, which took place on July 19?C21 2010?at the University of Sydney, philosophers debated these (and related) questions. The workshop covered topics in the philosophy of language, perception, and metaphysics. The present volume contains revised and expanded versions of the papers presented at the workshop.     

When Group Influence Is More or Less Likely: The Case of Moral Judgments

We investigated whether group influence can change judgments even for high-consensus (i.e., unambiguous) moral norms. We found that participants often matched the judgment of the other current group members even when this moral judgment was normatively incorrect (nonstandard), and this occurred more for more ambiguous issues. Moreover, this social influence on public judgments was generally followed by private agreement and re-interpreting general values to be consistent with those judgements. We also found that participants who experienced a fit between their regulatory focus and their feelings of power (i.e., promotion/high power; prevention/low power) were less influenced by the group.     

The Content of Deduction

For deductive reasoning to be justified, it must be guaranteed to preserve truth from premises to conclusion; and for it to be useful to us, it must be capable of informing us of something. How can we capture this notion of information content, whilst respecting the fact that the content of the premises, if true, already secures the truth of the conclusion? This is the problem I address here. I begin by considering and rejecting several accounts of informational content. I then develop an account on which informational contents are indeterminate in their membership. This allows there to be cases in which it is indeterminate whether a given deduction is informative. Nevertheless, on the picture I present, there are determinate cases of informative (and determinate cases of uninformative) inferences. I argue that the model I offer is the best way for an account of content to respect the meaning of the logical constants and the inference rules associated with them without collapsing into a classical picture of content, unable to account for informative deductive inferences.     

Preference-based belief revision for rule-based agents

Agents which perform inferences on the basis of unreliable information need an ability to revise their beliefs if they discover an inconsistency. Such a belief revision algorithm ideally should be rational, should respect any preference ordering over the agent’s beliefs (removing less preferred beliefs where possible) and should be fast. However, while standard approaches to rational belief revision for classical reasoners allow preferences to be taken into account, they typically have quite high complexity. In this paper, we consider belief revision for agents which reason in a simpler logic than full first-order logic, namely rule-based reasoners. We show that it is possible to define a contraction operation for rule-based reasoners, which we call McAllester contraction, which satisfies all the basic Alchourrón, Gärdenfors and Makinson (AGM) postulates for contraction (apart from the recovery postulate) and at the same time can be computed in polynomial time. We prove a representation theorem for McAllester contraction with respect to the basic AGM postulates (minus recovery), and two additional postulates. We then show that our contraction operation removes a set of beliefs which is least preferred, with respect to a natural interpretation of preference. Finally, we show how McAllester contraction can be used to define a revision operation which is also polynomial time, and prove a representation theorem for the revision operation.     

Why Adoptees Search: An Existential Treatment Perspective

This article frames the adult adoptee's search for his or her biological roots in an existential treatment perspective. This context offers depth of understanding of the adoptee's dilemma while allowing the counselor an expanded foundation from which to understand an adopted client's desire for personal historical information. An existential view of adoption allows the counselor to view the adoptee's struggle as a variation on the nearly universal human concerns of death, isolation, meaninglessness, being, anxiety, and freedom. Treatment approaches are suggested and discussed.     

Logical information and epistemic space

Gaining information can be modelled as a narrowing of epistemic space. Intuitively, becoming informed that such-and-such is the case rules out certain scenarios or would-be possibilities. Chalmers’s account of epistemic space treats it as a space of a priori possibility and so has trouble in dealing with the information which we intuitively feel can be gained from logical inference. I propose a more inclusive notion of epistemic space, based on Priest’s notion of open worlds yet which contains only those epistemic scenarios which are not obviously impossible. Whether something is obvious is not always a determinate matter and so the resulting picture is of an epistemic space with fuzzy boundaries.