Halliday & Matthiessen (1999: 169-70):
… where the relation is elaborating, the Range simply restates the Process or else further specifies it in terms of its class, quality or quantity. Here, we often find related pairs of 'Process : Process + Range'; the latter may involve nominalising the process (a form of grammatical metaphor). Examples:
In type (3), being (more particularly, ascriptive being), the Range is the Attribute that is ascribed. This construction, Process + Range/Attribute, is much more common that the agnate form with Process only (that is, 'be + important' is the preferred model rather than 'matter'). The Process just embodies the category meaning of ascriptive being — 'be a member of' — and the Range carries the specific information about the experiential class. It is interesting to note that the ranged construction sorts out the ambiguity of the simple present tense between habitual (doing) and occupational (being): she dances/does a dance every night, she dances/is a dancer (by profession).
