Martin (1992: 208-9):
Invoking the conduit metaphor (pace Reddy 1979), one might argue that [reformulation] is about different ways of saying the same thing, while [comparison] is about similarities between ways of saying different things. But since reformulations are not in any useful sense "synonymous", this formulation is somewhat misleading (as ever when content and form are dualised in functional linguistics). It would be better to say that with [reformulation], the first formulation and the second have almost all their meaning in common; a little fine tuning is all that's required. With [comparison] on the other hand, the meanings compared are different; but the way in which they are presented is in some respect the same… .
 'The conduit metaphor […] operates whenever people speak or write as if they "insert" their mental contents (feelings, meanings, thoughts, concepts, etc.) into "containers" (words, phrases, sentences, etc.) whose contents are then "extracted" by listeners and readers. Thus, language is viewed as a "conduit" conveying mental content between people.' [source]
 In SFL theory, content is "dualised" into the strata of semantics (meaning) and lexicogrammar (wording), and the latter into function and form (higher rank functions realised by lower rank forms).
 In SFL theory, conjunctive relations of this type are categorised as elaboration: clarification. The example previously given for reformulation (see yesterday's post), in contrast, involves elaboration: apposition.
 In SFL theory, the meaning of manner: comparison is simply N is like M.