Discussion of types

        ISAAC's world contains objects, agents, states, and actions. There are two reasons for deciding to utilize this particular four type view of reality. First, there is a strong functional argument to be made. The four types allow a wide range of real-world elements to be described, as I have been discussing in the above sections. Also, the four types match nicely to lexical elements in the English language. Nouns are either objects or agents, verbs are mostly actions with the to be verb acting as a state description, and adjectives are state descriptors. Since a reasoner is situated within the world of written texts, this knowledge scheme allows the lexical aspect of the environment to be utilized. Second, there is also evidence from developmental psychology that a somewhat similar division occurs during the growth of infants. For example, there appears to be an early differentiation between objects in the world and events which occur in the world ([#!change:carey1!#]).