Modes of concept definition and varieties of vagueness

The paper considers the problem of defining concepts within formal ontologies. A number of distinct modes of definition are identified, which represent alternative viewpoints on the classification of objects. The nature of these modes is examined and interactions and correlations between them are considered. This analysis is used to characterise a number of key problems that confront the attempt to analyse the meanings of natural language concepts by means of a precise formal ontology. Some proposals are made as to how these problems might be overcome. It is argued that specification of precise formal semantics requires clear separation between aspects of meaning that are based on different modes of classification. But, to provide an adequate ontological framework to describe the semantics of natural language terms, additional formal apparatus is required to synthesise their meaning by combining the different modes. This meta-level ontological formalism must articulate the interactions between the different modes.