This paper offers two main contributions. On the one hand, it establishes a general formal framework for developing a foundational ontology of socially constructed entities, in the broadest sense of this notion; on the other hand, it further contributes to understanding the ontological nature of roles. The key choice here is to put all social entities in the domain of discourse: besides social individuals, we also consider ‘reified ’ social concepts and roles, as well as their descriptions, i.e, the ‘social conventions ’ or ‘contexts ’ that define them. This allows us to formally characterize in a first-order theory the relationships among all these entities. 1

This thesis describes a system capable of modelling agents engaged in planning and plan recognition in a world containing multiple independent agents. It uses a database of formulae representing propositions about its domain, and a reason maintenance system to represent interdependencies between them. The system has been developed from recent ideas in domain-independent single-agent planners, but the planning process is controlled by rules that form a model of rational thought. Agents are modelled as having beliefs and goals, reasoning, acting and perceiving actions. They reason about each other's reasoning using the same model of rationality as the system uses to model them.

In this article, we canvass a few of the interesting topics that philosophers can pursue as part of the simultaneous study of logic and metaphysics. To keep the discussion to a manageable length, we limit our survey to deductive, as opposed to inductive, logic. Though most of this article