Although there is a high degree of independence between the three metafunctions on the level of paradigmatic choice systems, the process of realization combines the paradigmatic choices from all three metafunctions into a single realization on the level of syntagmatic chain structure. This process of merging in realization is performed by a specific realization operation called conflation.
The conflation operation is preceeded by insertion operations, which insert grammatical functions as a step in the realization of paradigmatic choices in the three metafunctions. For example, certain choices in the systems of the ideational metafunction are realized by the insertion of the grammatical function Actor, other choices in the systems of the interpersonal metafunction are realized by the insertion of the grammatical function Subject, and other choices in the systems of the textual metafunction are realized by the insertion of the grammatical function Theme. The conflation operation then combines these grammatical functions in various ways, specified by the realization rules for further choices made in the interpersonal and textual metafunctions. This is illustrated in Figure 1.10 (taken from [Halliday 1985]).
In Figure 1.10 example (a), all three grammatical functions are conflated into a single element of structure: Subject, Actor and Theme are all realized by the same element ``I''. This is the unmarked case in English, an active declarative clause. In example (b), the two grammatical functions Subject and Theme are conflated, and again realized by the element ``I'', but Actor is not conflated with them in this passive clause. In example (c), Subject and Actor are conflated, but not together with Theme. Although the clause is active, a marked theme has been chosen in the textual metafunction. In example (d), Theme and Actor are conflated, but not with Subject. The clause is passive like (b), but this time the Actor is thematized.
