Why ‘Realisation’ Applies To Both Strata And Rank And Where The Difference Lies

The overall architecture of SFL theory can be understood in terms of theoretical constructs within the model, namely: relational processes (identifying and attributive) and logico-semantic relations (expansion and projection).

‘Realise’ is an intensive identifying process, which means that it combines ‘identifying’ with ‘elaboration’.

In the case of strata, where a lower stratum realises a higher stratum, the relation between them is thus identifying + elaboration.

The rank scale, on the other hand, is organised in terms of composition, which is a subtype of extension. ‘Realise’ is used on the rank scale to relate the function of a higher rank to the form of a lower rank (eg Process is realised by verbal group). This relation between function and form is thus also identifying + elaboration.

The similarity thus lies in elaboration + identifying being an organising principle for both stratification and the rank scale.

The difference lies in the fact that, whereas stratification involves only elaboration + identifying, the rank scale combines extension (relation between forms) with elaboration + identifying (function–form relations).

(The term ‘realisation’ is used wherever there is an intensive identifying (token-value) relation in the theory. eg between system and structure on a given stratum, between strata, between function and form in the rank scale.)

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Halliday & Matthiessen (1999: 4n):

The ambiguity [of ‘level’ as either stratum or rank] resides in the overlap of two grammatical relations, those of elaboration (‘be’) and of extension (‘have’) …