PF is used in cases of fronted prepositional and participle phrases, typically (but not always) occurring together with subject-verb inversion. The PFb link is used for copular inversion, while the plain PF link is used for locative and directive inversion. The CP link is used for quotative inversion.
+---------PFb-------+-SI-+
| | |
Among the candidates was Jane Smith, a professor
Carrying the box was a small child
?Described by John was a new program
+---------PF--------+-SI--+
| | |
Under the tree slept Jim
Into the room walked two students
+---------PFt-------+-SI--+
| | |
There lay the money
Such phrases vary widely in their acceptability, depending on
the participle or preposition; we allow all participles and
most prepositions to be used this way, but only with a cost of
1 or 2. The PFt link cannot connect to PFb
and thus serves to prevent "there is" from being interpreted
as an S-V inversion.
Such fronting can occur even without S-V inversion:
+------------PFt---------+
| |
There he transferred the remains
There the remains can be found
In this example, "the remains" acts as the subject to "found" and occurs
in normal sentence order.
These phrases are not to be confused with openers. Openers attach to the subject of an ordinary main clause, which does not have s-v inversion and can have any verb: "Carrying the box, Jane left". Fronted prepositional or participle constructions involve s-v inversion.
In such cases, the fronted phrase must attach to the wall; the Wp link is used for this purpose. S-V inversion is necessary here ("*Among the candidates Jane Smith was"); thus the participle makes a Wp connection to the wall, enforcing s-v inversion in post-processing.
among: J+ & (Mp- or MVp- or ... [[Wp- & PF+]])
carrying: (Pg- & (O+...)) or
((O+...) & (Ss*g+ or COp+ or [[Wp- & PF+]]));
For participles, note that the Wp- & PF+ complex is
directly disjoined with the COp+ and Ss*g+,
and is to the right of the
complement expression; it is fully disjoined with the Pg-,
which is to the left of its complement expression. See
CO:
Participles as Openers for an explanation.
Normally forms of "be" require a complement to the right; but they can also be satisfied by a question-word to the left like "where", "when" or "how".
+-Wq--+-PF-+-SI+
| | | |
///// Where are you
+--PF----+
+--QI-+ +-S-+
| | | |
I wonder where you are
Forms of "be" thus have PF- directly disjoined with "O+ or Pg+
or Pv+...".
The question-words "where" and "when" have PF- conjoined with Wq- or QI-. In questions, then, a Wq- connection to the wall is made, enforcing s-v inversion (see "SI"); in indirect questions, an QI connection is made, preventing s-v inversion.
Note that other verbs cannot be used in this way: "*Where ran you", "*What think you", "*What have you?" The first two cases are prevented because ordinary verbs don't have SI+ connectors; the third is prevented because, although "have" has an SI+, it is conjoined only with PP+ (used in past-participles) and not with O+ and B- (used with direct objects). Only on forms of "be" is the SI+ conjoined with the entire complement expression.