Martin (1992: 571):
For Halliday, the complication has to do with introducing the concept of first and second order contexts, with first order field and tenor oriented to situation and second order field, tenor and mode defined by reference to language. Table 7.21 sums up his (1978: 143-5) position:
Table 7.21. First and second oder [sic] register in Halliday (1978)
first order second order field social action subject matter tenor social roles speech function roles mode – medium, rhetorical genre
 To be clear, both first and second order field and tenor are systems of context, and both are related to language by realisation — the relation between levels of symbolic abstraction. The relation between different orders of experience is projection.
 Here Martin misrepresents Halliday (1978: 142-5) by substituting his own model for Halliday's. For Halliday's 'context', Martin substitutes 'register', and for Halliday's '(rhetorical) mode', Martin substitutes his 'genre'.