Martin (1992: 288-9):
One critical consideration which has been set aside in the discussion of lexical relations to this point is that of field specificity. In general cohesion analysts have tended not to be very specific about this point. Categories tend to be illustrated with examples from core vocabulary, which are kept as field neutral as possible: verbs, adverbs and adjectives are favoured over nouns, and "commonsense" nouns are used rather than technical ones. It is no accident that Hasan chooses action verbs in exploring the grammarian's dream; fields tend to differentiate themselves nominally, through technical lexis, rather than through verbs, adjectives and adverbs. But even with verbs, the question of field slips in.
 This discussion confuses two distinct domains of SFL theory:
- the grammatical system of lexical cohesion, a nonstructural resource of the textual metafunction that relates lexical items in terms of repetition, synonymy, hyponymy, meronymy and collocation;
- the systemic specification of lexical items by extending the delicacy of grammatical networks (experiential metafunction).
 In SFL theory, lexical cohesion is a grammatical system concerned with textual relations between lexical items, whereas field is the ideational dimension of context.
 These remarks are about extending the delicacy of grammatical networks, while purporting to be about lexical cohesion.
 In SFL theory, field variation is modelled as a point on the cline of instantiation at the stratum of context. For example, field variation is the ideational dimension of situation type variation, where the variation is of the probabilities of field features being selected.