Halliday & Matthiessen (1999: 437-8):
In the logical-philosophical approach, within generative linguistics, interpretive semantics has focussed on the question of how semantic representations can be derived from below, from syntactic ones; and an important aspect of the debate in the late 60s and early 70s was precisely concerned with the directionality of interstratal mappings and the nature of the inter-stratal boundary.
One key question that emerged, particularly in the 1970s and early 1980s, was whether syntax is autonomous or not. In the standard Chomskyan theory it was; but this was rejected by Montague and those who were influenced by his idea of building syntactic and semantic specifications "in tandem" (as in the successive developments of GPSG and HPSG).
Within the rhetorical-ethnographic approach, we have taken the position that not only is lexicogrammar not autonomous, but it is natural in relation to semantics: our approach to the ideation base rests on this theoretical assumption. This is what explains the further possibility of grammatical metaphor, opened up at the interface between semantics and lexicogrammar.