Fawcett (2010: 37):
At this point I should clarify the sense in which I am using the terms "grammar" and "meaning". Let us take "grammar" first, since it is used in the caption for Figure 4. In "Categories", "grammar" was the name of a subcomponent of the level of form, but here its meaning has been extended in two ways. The most obvious is that a grammar now includes a level of meaning as well as a level of form. Thus a 'grammar' is essentially a model of the sentence-generating component of a full model of language and its use. The second extension — which is less obvious — is that the term "grammar" is regularly used as a short form for "lexicogrammar".
 Contrary to the implication, this "extension" of the meaning of 'grammar' to 'lexicogrammar' is not Fawcett's. It appears in Categories of the Theory of Grammar (Halliday 1961), where lexis is conceived as most delicate grammar. Halliday (2004 : 54):
The theoretical place of the move from grammar to lexis is therefore not a feature of rank but one of delicacy. It is defined theoretically as the place where increase in delicacy yields no further systems;
 To be clear, Fawcett stratifies grammar into meaning and form, whereas Halliday locates meaning in semantics, and distinguishes between grammatical functions and grammatical forms (the rank scale). Crucially, it is the distinction between semantics and lexicogrammar that allows Halliday to account for grammatical metaphor in his model.