Halliday & Matthiessen (1999: 97):
Children are able to construe the semantic system because they start in situations with a material setting that is shared. As they build up their ideation base, they can begin to construe categories internal to the system out of existing ideational values; and they can begin to move into abstract domains of a purely symbolic world, where the significations of semantic categories are abstract categories in social and socio-semiotic systems. But precisely because these abstract categories are construed as meanings, they can still be built up, negotiated and validated in collaboration with other members of the meaning group. The move from the realm of concrete phenomena to the various realms of abstract phenomena is made possible through the homogenising power of meaning.