Halliday & Matthiessen (1999: 73):
The first stage in categorisation is naming individuals as members of classes; instances of 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. … 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 [the child] as the Carrier of a figure of being, and is ascribed as a member of some general class of experience, construed as the Attribute of the figure. [The child] 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.