Halliday & Matthiessen (2014: 347):
The transitive is a linear interpretation; and since the only function that can be defined by extension in this way is Goal (together with, perhaps, the analogous functions of Target in a verbal process and Phenomenon* in a mental process of the please [‘impinging’] type), systems which are predominantly transitive in character tend to emphasise the distinction between participants (ie direct participants, Actor and Goal only) and circumstances (all other functions).
Blogger Comment:
* It strikes me that this should be Senser, not Phenomenon.