Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1999.Includes bibliographical references (p. 193-199).The ability to individuate entities (i.e. conceptualize one entity as distinct from two) and trace their identity (i.e. judge that an entity is the same one as an entity encountered before) is a fundamental component of the human mind and is critical to proper name reference (i.e. a proper name, like lvfax, refers to a unique individual, namely Max). Philosophers have proposed that sortals-concepts which refer to kinds of individuals-support these abilities (Gupta, 1980; Hirsch, 1982; Macnamara, 1986; Wiggins, 1967, 1980). However, while adults may well have sortal concepts and learn proper names for individuals, it is an open question whether children do so also. Proponents of the Continuity hypothesis (e.g. Macnamara, 1982; Pinker, 1984) argue that children and adults have fundamentally the same conceptual resources, whereas proponents of the Discontinuity hypothesis (e.g. Piaget, 1954; Quine, 1960, 1969) argue that child.en and adults have qualitatively different conceptual systems. In this thesis, evidence is reviewed that very young infants have at least one sortal, physical object, which suggests that infants have the conceptual structure needed to support representations of kinds and individuals. Experiments probing infant understanding of the concept, person, suggest that infants have the ability to reason about the action and appearance of others, but data presented in the thesis falls short of providing conclusive evidence that infants under a year are able to individuate people. Evidence is presented that by age three, children represent unique individuals and interpret proper names in an adult like manner as referring to unique individuals. This rules out a discontinuity alternative, namely that preschoolers represent proper names as referring to highly similar objects or to restricted subkinds. Evidence is also presented that children as young as two years are like adults in being willing to accept a range of individuals as nameable if given information which highlights the named objects' importance, such as the attribution of mental states to the object. Together these findings provide support for the continuity hypothesis and suggest a number of avenues of research into children's understanding of kinds, individuals, and their names.by Christina M. Sorrentino.Ph.D.