Martin (1992: 177):
These problems are not isolated. Halliday (1985) for example subclassifies enhancing relations on the basis of of his categories for types of Circumstance in the system of TRANSITIVITY. Thus likewise comes out as enhancing: manner and in that respect as enhancing: matter. This contrasts with the Cohesion In English analysis which groups likewise among the additives (extension: addition for Halliday 1985) and in that respect among causals (enhancing: causal-conditional for Halliday 1985). Since the prepositions realising circumstantial relations organise the world differently from conjunctions, this divergence is not surprising.
 In SFL theory, it is the other way around: it is circumstances that are classified according to the transphenomenal fractal types, expansion and projection, that they manifest — Extent, Location, Manner, Cause and Contingency as enhancing, Accompaniment as extending, Rôle as elaborating, Matter and Angle as projection.
 These are wordings that can be used to serve such conjunctive functions. Here they are misinterpreted as belonging to functional categories. This is the same type of error as allocating a verb (e.g. mean) to a PROCESS TYPE instead of considering its function in a clause.