Halliday & Matthiessen (1999: 73):
Painter (1996) provides a key to the understanding of how linguistic resources are deployed in 'categorisation' in language development, drawing on her longitudinal case study of one child, Stephen, between 2 1/2 and 5 years.The first stage in categorisation is naming individuals as members of classes; instances of the visual experience shared by the young child and his father or mother are ascribed to some general class of experience by means of a figure of being. At about 2 1/2, Stephen produced examples such as: Stephen (examining pattern on a rug): That's a square. What's that? — Mother: That's a circle. Here some perceived phenomenon of experience is brought "into intersubjective focus" by being referred to exophorically — pointing verbally, so to speak, to some feature of the material setting, sometimes accompanied by or replaced by a pointing as a gesture. This phenomenon is construed by Stephen as the Carrier of the figure of being, and is ascribed as a member of some general class of experience, construed as the Attribute of the figure. Stephen is 'importing' experience of instances into the semantic system by ascribing them to general classes in that system. This is an act of naming, and later this act itself gets named by call (see also Halliday, 1977, on calling as an early example of language being turned back on itself).Children thus build up experience as meaning, in contexts such as the one exemplified above.