## Problem Set 6

Assigned: Nov. 17
Due: Dec. 3.

Note: This is due in TWO weeks. If you are submitting this by email, please send it to Ernie Davis, davise@cs.nyu.edu, not to the TA.

### Problem 1

Explain how each of the ambiguities specified below can be resolved by selectional restrictions. Your explanation should specify what are the constraints and the features involved.

For example: The lexical ambiguity of the word "bat" in the sentence, "The sick bat lay on the ground," (wooden club vs. flying mammal) is resolved by the constraint "If X is sick, then X must have the feature ANIMATE" and that facts that the meaning "club" does not have the feature ANIMATE whereas the meaning "mammal" does have the feature ANIMATE.

The anaphoric ambiguity of the word "it" in the sentence, "John sat down at his desk with a bagel and started to eat it" ("it"=bagel vs. "it"=desk) is resolved by the constraint "The object of eating must have the feature "EDIBLE", and the fact that "desk" does not have the feature "EDIBLE" but that "bagel" does have the feature "EDIBLE".

The syntactic ambiguity of "The man from Cincinatti with the red beard sang `Clementine'" (Does "with the red beard" modify "band" or "Cincinatti"?) is resolved by the constraint that the owner of a body part (beard) must have the feature ANIMATE, a man has the feature ANIMATE, but a city does not.

• A. Resolve the lexical ambiguity of "pitcher" in "The pitcher drank a cup of coffee." ("pitcher" = baseball player vs. "pitcher" = container of liquid.
• B. Resolve the lexical ambiguity of "pitcher" in "Joe poured a cup of coffee from the pitcher". (Same ambiguity as in (A); different decision.)
• C. Resolve the anaphoric ambiguity of "They" in "The children got new toys for Christmas. They were very excited." (They = "children" or "toys").
• D. Resolve the anaphoric ambiguity of "They" in "The children got new toys for Christmas, but they all broke within half an hour."
• E. Resolve the syntactic ambiguity of the conjunction in "The captain of the ship and the first mate swam to shore." (Is it "The captain of [the ship and the first mate]" or "[The captain of the ship] and the first mate."
• F. Resolve the syntactic ambiguity of the conjunction in "The man with the red beard and the glass eye swam to shore". (Is it "[the red beard and the glass eye]" or "[The man with the red beard] and the glass eye"?
• G. Resolve the lexical ambiguity of the word "on" in the sentence "We have to write a paper on prohibition for "Twentieth Century American History" by Monday." ("on" = "about" vs. "on" = "on top of")

### Problem 2

Explain how each of the ambiguities specified below can be resolved using selectional restrictions or world knowledge. You should be as precise as possible about what facts are being applied.
• A. John asked his father whether he would give him a car for his 16th birthday. ("him" and "his" = John; "he" = father.)
• B. President Bush proposed to cut taxes on inheritances because they are too high. ("proposed" = "formally suggested" rather than "offers marriage"; "cut" = "reduce" rather than literally slice; "they" = taxes rather than inheritances; "high" = large amount of money rather than physically elevated.)
• C. Resolve the syntactic ambiguities of the prepositional phrase attachments in the sentence "We have to write a paper on prohibition for "Twentieth Century American History" by Monday." (Compare: "We have to read a book on prescription drug benefits for senior citizens by an expert on Medicare.")