Transcript Embedded Clauses in TAG

Embedded Clauses in TAG
Embedded Clauses
Matrix Clause
S
NP
VP
V
S-bar
Embedded Clause
S
COMP
We think that
NP
VP
they have left.
How we know that the semantic role
assignments are different with Seem and Try
• The cat seems to be out
of the bag.
• There seems to be a
problem.
• That seems to be my
husband.
• The doctor seemed to
examine Sam.
• Sam seemed to be
examined by the doctor.
• The cat tried to be out of
the bag.
• *There tried to be a
problem.
• That tried to be my
husband.
• The doctor tried to
examine Sam.
• Sam tried to be examined
by the doctor.
Raising to subject
S
NP
S
VP
V
NP
S-bar
VP
V
VP-bar
S
COMP
It
seems that
NP
VP
VP
COMP
they have left. They seem to
have left.
S
NP
VP
V
VP-bar
Two ways to represent that
“seem” and “leave” share a
subject.
VP
COMP
They seem to
have left.
S
NP
VP
V
S
NP
They seem e
VP
to have left.
Subj
Verb
Complement
they
seem
subj
verb leave
Comparison
• Second method:
– Allow empty strings as terminal nodes in the tree.
– An empty string needs to take the place of the missing subject of the
lower clause.
– The empty string is linked to the subject of the main clause to show that
the main and embedded clauses share a subject.
– The tree represents: word order, constituent structure, grammatical
relations, semantic roles.
• First method:
– No empty strings in the tree.
– The tree represents only word order and constituent structure.
– Grammatical relations and semantic roles are represented in a separate
structure.
– Structure sharing in the representation of grammatical relations shows
that the two verbs share a subject.
• Is one method simpler than the other?
– No. Both methods have to represent word order, semantic relations,
grammatical relations, and semantic roles.
• People who argue that one is simpler are usually wrong – they don’t know
how to count steps in a derivation.
Two ways to represent that
“try” and “leave” share a
subject.
S
NP
VP
V
VP-bar
Subj
Verb
Complement
VP
COMP
They try to
they
seem
subj
verb leave
leave.
S
NP
PRO is an empty string, but not the same kind
of empty string as e 
VP
V
S
Coindexing indicates that PRO refers to “they”.
NP
They(i) try
VP
PRO(i) to leave.
“Seem” type verbs in TAG
VP
S
NP
VP
V
John
Adjunction site
AP
to be happy
Initial Tree
V
VP
seem
Auxiliary Tree
These trees represent the number of
arguments for each verb:
“Seem” has one argument, represented
as a VP.
“To be happy” has one argument, “John”.
VP
S
NP
VP
Adjunction site
V
seem
VP
V
John
AP
to be happy
VP
S
NP
S
NP
V
VP VP
V
VP
seems V
Adjunction
VP
seem
AP
to be happy
VP
V
AP
to be happy
John
VP
John
This tree shows word order and
constituent structure.
It also shows that “John” is the
subject of “seem.”
It doesn’t show that “John” is the
subject of “to be happy.”
“Try” type verbs in TAG
S
S
NP
NP
VP
V
John
VP
TO
S
PRO
tried
Auxiliary Tree
Adjunction site
VP
leave
Initial Tree
These trees show the number of arguments for
each verb:
“Try” has two arguments.
“Leave” has one argument.
S
S
NP
VP
V
John
Adjunction site
tried
S
S
NP
VP
TO
PRO
VP
leave
S
S
NP
VP
V
John
Adjunction site
S
S
triedNP
VP
TO
PRO
VP
leave
Adjunction is only
allowed at the top S
node so as not to mess
up compositional
semantics:
After you put together
“try to leave” you don’t
want to have to take it
apart again by inserting
another verb like
“expected” as in:
John tried to expect to
leave.
Inserting “seem” into the
middle of the tree
doesn’t require you to
disassemble any of the
semantic pieces that
were already
assembled?
S
NP
VP
V
John
S
triedNP
VP
TO
PRO
VP
leave