This report describes an investigation of the acquisition by children of a symbolic system, specifically English nomenclature--that set of nouns that serves the function of naming, denoting, or referring to objects. The five studies involve nine experiments dealing with one or another of the aspects of this problem. Two questions guided these studies from the outset: (1) What is the order of acquisition of category labels? and (2) How does the meaning of these labels change as the child grows older? Two different definitions of conceptual complexity were considered to see whether either is predictive of the order of acquisition of category labels in development. In a number of studies it was found that neither of these definitions of conceptual complexity is a good predictor of the order of acquisition of category labels. A good predictor was given by various frequency of occurrence measures in general and in particular frequency of occurrence of the words in child speech, according to Rinsland (1945). The vocabulary of young children is consistent with the way in which mothers name objects for them. (Author/LL)