1.  Introduction
        
One approach to the study of language acquisition focusses on 
identifying and understanding those properties of language which seem to
be universal, i.e. present in all human languages, and which are therefore 
presumed to be in some sense innate to the human organism.  A broader 
approach seeks understanding of the process of development, focussing
on how the less universal aspects of language are acquired.  (See 
discussion in  (Braine, 1994) .)  While conceding that human children must 
be endowed with abilities that make possible certain kinds of linguistic 
knowledge not demonstrable in other species, the focus is less on innate
abilities and more on the process of acquisition of the whole of a 
language.  The child is viewed as an organism initially endowed with a 
range of abilities (including motor, sensory, affective, and social) which 
develop over time, and driven by functional and social needs to learn ever 
more about language structure and use.
        My own interests in the dynamics and complexity of language 
acquisition put me in this second camp, where I can consider the 
simultaneous interaction and cross-fertilization of different kinds of 
development: anatomical, neurological, social, affective, cognitive, 
cultural, and linguistic factors (see discussion in  Barber & Peters, 
1992 ).  Viewing language acquisition as but a part of a much more 
complex developmental process has led me away from the assumption 
that language acquisition and analysis are all-or-none states (either
 you know it or you don't); rather I find much evidence that partial 
analysis and partial acquisition are pervasive -- even for native-
speaking adults.  (See, e.g.  Peters & Menn (1993)  for discussion.)  
Finally, my approach to the description of language development is 
linguistically conservative, relying upon as few assumptions as 
possible about innate presence of linguistic categories and knowledge 
of linguistic structure.
        From such a starting point, one approach to understanding early 
syntactic development is to see how much of it can be adequately 
described by means of a series of phrase structure grammars, each 
successive one of which has a larger number of linguistic categories, and 
a larger number of positional slots to be filled or expanded.  The child is 
assumed to gradually discover that he needs not only to include more 
open-class lexical items (especially nouns and adjectives together with 
each verb), but that there are more and more closed class positions in 
the vicinity of each that he must fill.  To what extent is such a scenario 
supported by evidence?  I will demonstrate this approach in the following 
description of the development of auxiliaries, modals, and catenative 
verbs in my data from an English-speaking child.