Drawing Trees & Ambiguity in Drawing Trees & Ambiguity in TreesTrees

Some Phrase Structure Rules of Some Phrase Structure Rules of EnglishEnglish

S’ -> (Comp) SS’ -> (Comp) S S -> {NP/S’} (T) VPS -> {NP/S’} (T) VP VPVP (AP+) V ({NP/S’}) (PP+) (AP+)(AP+) V ({NP/S’}) (PP+) (AP+) NP NP (D) (AP+) N (PP+)(D) (AP+) N (PP+) PP -> P (NP)PP -> P (NP) AP -> (AP) AAP -> (AP) A

Drawing treesDrawing treesStep 1: Identify the parts of speech for all the words in

the sentenceStep 2: figure out what words "go together in phrases"

(i.e. figure out what the constituents are) [remember the Golden Rule of modification!]Step 3: apply the rules backwards (bottom up) to build

the tree. Start with adjectives & APNext do NPs, then PPs, then VPsGenerally, start at the RIGHT edge

of the tree and work leftwardsapply the S rule last.

Step 4: now check your tree against your rules. Start at the top, and check that each set of lines can be generated by the rules.

Drawing treesDrawing trees

Important: Nothing can be left dangling in space. Everything has to be attached to

something higher up.Lines can't cross one another. Using the tree-drawing website can help!

Some treesSome trees

The very big man gave the marble to his sonThe very big man gave the marble to his sonDet A A N V det N P det N

PP

NPNP

NP

VP

S

APAP

Some treesSome trees

The big lazy dog bit a mouthful of foodThe big lazy dog bit a mouthful of foodDet A A N V det N P N

PP

NP

VP

AP AP

NP

S

NP

Some treesSome trees

I have seen a syntax assignment from RussiaI have seen a syntax assignment from RussiaN T V det A N P N

PP

NP

NP

SVP

AP

NP

AmbiguityAmbiguity

Ambiguity: when a sentence has two Ambiguity: when a sentence has two meaningsmeanings

Paraphrase: A restatement of the meaning Paraphrase: A restatement of the meaning of a sentence, used to disambiguate of a sentence, used to disambiguate ambiguous sentences.ambiguous sentences.

» John went to the bank. John went to the bank.

» Paraphrase 1: John went to the financial institutionParaphrase 1: John went to the financial institution

» Paraphrase 2: John went to the side of the riverParaphrase 2: John went to the side of the river– We use paraphrases to disambiguate. BUT be sure that when you We use paraphrases to disambiguate. BUT be sure that when you

draw trees you draw them of the ORIGINAL sentence, not the draw trees you draw them of the ORIGINAL sentence, not the paraphraseparaphrase

AmbiguityAmbiguity

Two kinds: Two kinds: – Lexical ambiguityLexical ambiguity uses words with more than uses words with more than

one meaning.one meaning.– Structural ambiguityStructural ambiguity ambiguous due to the ambiguous due to the

structure of the tree.structure of the tree.

Lexically Ambiguous HeadlinesLexically Ambiguous Headlines» Safety Experts Say School Bus Passengers Should Be BeltedSafety Experts Say School Bus Passengers Should Be Belted

» Drunk Gets Nine Months in Violin CaseDrunk Gets Nine Months in Violin Case

» Iraqi Head Seeks ArmsIraqi Head Seeks Arms

» Farmer Bill Dies in HouseFarmer Bill Dies in House

» Stud Tires OutStud Tires Out

» Prostitutes Appeal to PopeProstitutes Appeal to Pope

» British Left Waffles on Falkland IslandsBritish Left Waffles on Falkland Islands

» Reagan Wins on Budget, But More Lies AheadReagan Wins on Budget, But More Lies Ahead

» Red Tape Holds Up New BridgeRed Tape Holds Up New Bridge

» Deer Kill 17,000Deer Kill 17,000

» Man Struck by Lightning Faces Battery ChargeMan Struck by Lightning Faces Battery Charge

» Ban on Soliciting Dead in TrotwoodBan on Soliciting Dead in Trotwood

Structurally Ambiguous Structurally Ambiguous HeadlinesHeadlines

Two Sisters Reunited after 18 Years in Two Sisters Reunited after 18 Years in Checkout CounterCheckout Counter

Enraged Cow Injures Farmer With AxEnraged Cow Injures Farmer With Ax Hospitals are Sued by 7 Foot DoctorsHospitals are Sued by 7 Foot Doctors Killer Sentenced to Die for Second Time in Killer Sentenced to Die for Second Time in

10 Years.10 Years.

???

The Principle of ModificationThe Principle of Modification“The Golden Rule”“The Golden Rule”

If one constituent modifies another then If one constituent modifies another then those two constituents are sisters. (i.e. They those two constituents are sisters. (i.e. They must be part of the same constituent)must be part of the same constituent)

AP

AP A

sisters

NP

AP N

sisters

Ambiguity in StructureAmbiguity in Structure

The man put the book in the box on the The man put the book in the box on the table.table.

Meaning 1:Meaning 1: put the book (currently in the box) put the book (currently in the box) on the table. The box isn’t on the tableon the table. The box isn’t on the table

book

Meaning 2: put the book into the box. The box is on the table.

book

book

VP

V NP PP

put det N PP P NP

the book P NP on D N

in the box the table

VP

V NP PP

put det N P NP

the book in D N PP

the box P NP

on the table

book

Ambiguity in StructureAmbiguity in Structure

I killed the king with the knifeI killed the king with the knife– easy reading “used a knife for the killing”easy reading “used a knife for the killing”– harder reading “king holding a knife”harder reading “king holding a knife”

I killed the king with the red hairI killed the king with the red hair– easy reading “king who has red hair”easy reading “king who has red hair”– harder reading “used red hair to kill him”harder reading “used red hair to kill him”

I killed the king with a knife

S

D N P NP

killed using a knife

NP VP

N V NP PP

I killed

the king with

D Na knife

king holding a knife

S

NP VP

I killed

D N PPthe king

D Na knife

N V NP

P NPwith

I killed the king with red hairkilled using red hair

S

NP VP

N V NP PP

I killed

D N P NPthe king with

AP N hair

king who has red hair

S

NP VP

I killed

D N PPthe king

AP N hair

N V NP

P NPwith

A

redA

red

Test: Which Kind?Test: Which Kind?

Their flight from Egypt was remarkableTheir flight from Egypt was remarkable– The plane ride was really somethingThe plane ride was really something– Fleeing from Egypt was really somethingFleeing from Egypt was really something

We saw the Eiffel tower flying to ParisWe saw the Eiffel tower flying to Paris– We were flying [or the plane was, with us on it]We were flying [or the plane was, with us on it]– The Eiffel tower was flyingThe Eiffel tower was flying

The president could not ratify the treatyThe president could not ratify the treaty– It was impossible for the president to ratifyIt was impossible for the president to ratify– It was possible that the president wouldn't ratify.It was possible that the president wouldn't ratify.

ArgumentsArguments

Two structuresTwo structures– [The president could [not ratify the treaty][The president could [not ratify the treaty]– [The president [could not] [ratify the treaty][The president [could not] [ratify the treaty]– What the president could not do is [ ratify the What the president could not do is [ ratify the

treaty].treaty].– What the president could do is [not ratify the What the president could do is [not ratify the

treaty].treaty]. The president couldn't ratify the treaty. [impossible The president couldn't ratify the treaty. [impossible

reading only]reading only]

SummarySummary

Tree drawingTree drawing

– practice, practice, practicepractice, practice, practice– apply rules from bottom up, start with APs, apply rules from bottom up, start with APs,

NPs, PPs first. Start from right edgeNPs, PPs first. Start from right edge– make sure everything is connected, no crossing make sure everything is connected, no crossing

lineslines– CHECK your trees against the phrase structure CHECK your trees against the phrase structure

rules.rules.

SummarySummary

Structurally vs. Lexically ambiguous.Structurally vs. Lexically ambiguous. Structurally ambiguousStructurally ambiguous

– different meanings have different trees.different meanings have different trees.

– relies on the principle of modification!relies on the principle of modification! A paraphrase is a restatement of meaning. A paraphrase is a restatement of meaning.

Don’t draw trees for the paraphraseDon’t draw trees for the paraphrase -- draw -- draw them for the actual sentence.them for the actual sentence.