Halliday & Matthiessen (2014: 330):
This also involves prepositional phrases functioning as participants; but here there is no alternation between prepositional phrase and nominal group. Instead, the preposition is closely bonded with a verb, so that it is functioning as part of the Process, as with turn into; similarly look at the sky consists of Process look at + Phenomenon the sky. There is no simple diagnostic criterion for deciding every instance; but a useful pointer is provided by the thematic structure, which gives an indication of how the clause is organised as a representation of the process.
Blogger Comment:
To be clear, it is not the prepositional phrase that functions as participant, but the nominal group that serves as the Range of the prepositional phrase.
look
|
at
|
the sky
|
Process: mental: perception
|
Phenomenon
| |
Predicator
|
Adjunct
| |
verbal group
|
prepositional phrase
| |
minor Process
|
Range
| |
nominal group
| ||