In the circumstantial type, the relationship between the two terms is one of time, place, manner, cause, accompaniment, matter or role [...] In the attributive mode, the circumstantial element is an attribute that is being ascribed to some entity: for example 'my story is about a poor shepherd boy'. These take two forms: one in which the circumstance is expressed in the form of the Attribute, as here ('about poor shepherd boy'); the other in which the circumstance is expressed in the form of the Process, e.g. 'my story concerns a poor shepherd boy' [...] In the identifying mode, the circumstance takes the form of a relationship between two entities; one entity is being related to another by a feature of time or place or manner, etc. As with the circumstantial attributive, this pattern may be organized semantically in either of two ways. The relationship is expressed either (a) as a feature of the participants, as in 'tomorrow is the tenth', or (b) as a feature of the process, as in 'the fair takes up the whole day'.
- Halliday (1985), Pag. 119-120