Form names the kind of word or phrase. Function names the job that unit does in a larger phrase or clause. One form can do several jobs, and one job can be filled by several forms.
Where does each prepositional phrase fit?
Of the wood is a PP that completes the outer preposition out.
In the tunnel is a PP that functions as an adverbial of waited.
Both highlighted units are PPs because each has a preposition and a complement. Their parents differ: one belongs under another preposition, and one belongs with the clause’s predicate. The preposition, the meaning of place, and final position do not by themselves choose that relationship.
Can one clause job have different forms?
Very quietly is an adverb phrase functioning as an adverbial of waited.
In the tunnel is a prepositional phrase with the same adverbial function.
a narrower consequence
Requiredness belongs to the verb frame
Can the location phrase be set aside?
With rehearsed, in the hall is optional: the event is complete without it.
With put, the same phrase is required by the verb’s frame.
Both final phrases are PPs and both are adverbials in the course model. With rehearsed, the event remains complete without the location. In the ordinary caused-placement sense of put, the destination is part of the verb’s required frame. Removal tests that frame in this meaning and context; it is not a test for PP form or for every function.
Ask two separate questions.
First ask what kind of unit the words form. Then ask what that complete unit does in the structure that contains it. The answers describe different relationships, so a phrase needs both.
Ten sentences from this lesson, one decision at a time.