As a discourse develops, focus spaces are stacked one on top of another so that the most recent is always on top of the stack. The stack itself can thus be used [as] a record of progression through discourse time. Now the stack is always manipulated from the top: if a new focus space is to be added to the stack, it is pushed onto the top of the stack; and if an old one is to be removed, it is popped off the top of the stack.
The speaker thus selects ‘thematic spaces’ as points of entry into larger regions of the ideational semantic network. From the listener’s point of view, these thematic spaces constitute indications of where to integrate the new information being presented in the text… . If we think of the listener’s processing of a text as being partly a matter of expanding his or her current semantic network with new information, the thematic spaces guide him/her to appropriate expansion points.
Thematic spaces in an ideational semantic network can be seen as a model of the systemic understanding of Theme and method of development articulated by Martin, where [Martin’s] “field” corresponds to what has been discussed here in terms of ideational semantic networks in the ideation base.
(i) The second-order character of textual information is captured by defining it in terms of the already existing semantic network in the ideation base (the first-order representation…). This is clearly only a first approximation… the textual metafunction may in fact motivate ideational metaphor as a means of ‘carrying’ textual organisation.
(ii) Textual prominences constituting textual statuses can then be modelled as partitioned textual spaces of the semantic network. … This is also only a first approximation: textual prominence is a matter of degree and we need to think of a textual space not as a clearly bounded region but rather as a central region, the peak of prominence, from which one can move to more peripheral regions, the troughs of non-prominence. Such gradience is necessary not only to deal with degrees of thematicity and newsworthiness but also to handle identifiability by ‘bridging’…