According to Halliday, at around 9-10 years the child is able to comprehend metaphorical modes of expression, and to produce them at around 14-15 years (1986, 1985, 1991). He sees the move into grammatical metaphor as a complex step in the evolution of the child's language system (1985). Instead of expanding simply through elaboration and extension, the system is now enhanced by 'turning back on itself'. It is no longer a matter of constantly adding new subsystems, but of deploying existing subsystems to serve new functions. Any instance of such cross-coding will resonate with the traces of both the 'literal' and the 'transferred' meaning. In order to apprehend the metaphorical meaning, the immanent literal meaning must also· be recognised. Halliday refers to this phenomenon as a 'semantic blend'. Whereas in the congruent form, we could say that we are dealing with the realization of a 'semantic simplex', in the metaphorical form, the realization is of a 'semantic complex'. In the transition to grammatical metaphor, the adolescent is able to mean more than one thing at a time in terms of the semantic cross-coding inherent in metaphorical constructions. The effect of this cross-coding is to multiply the potential of the system. The semantic complexity may be further increased when we have instances of recursive grammatical metaphor, where one metaphor is compounded by another, requiring multiple 'loopings' through the system in order to retrieve the congruent.