Introduction to AI & AI Principles (Semester 1) WEEK 4 (07/08) John Barnden Professor of Artificial Intelligence School of Computer Science University of Birmingham, UK

Expert versus Everyday/Common-Sense (review) uExpert AI: e.g., l Expert systems for medical diagnosis, etc. l Chess programs l Mathematical theorem provers l Aircraft movement planning systems l Specialized manufacturing robots uEveryday/Common-Sense AI: e.g., l Language processing, for no specific domain l Common-sense reasoning about the everyday world l Seeing the everyday world

WHY IS EVERYDAY AI CHALLENGING?

(review) Who … … ? How many of you … … ? How many students at the University own cats?

Notice on van: CAUTION CHILDREN What could this mean?

Some Possible Meanings (of the phrase in isolation, at least) uBe cautious, you might harm a child. uBe cautious, a child might harm you! uChildren, be cautious. uCaution some children, please. uThis locker (say) is for the children of the Caution family. uThese are the children who have been cautioned. uThese are the children who have done some cautioning. uThese are the children who are “a caution.”

at Birmingham airport EU Nationals this way Other passports this way

Three Touching Tales uJohn got to his front door, but realized he didn’t have his key. uMary went to a restaurant for lunch. Afterwards she didn’t have enough money to take a taxi. uMary went to a restaurant for lunch. Afterwards she didn’t have enough money to buy the car she wanted.

Some Lessons from the Above uRole of context: l co-text l discourse location, time & participants l characteristics of the environment, the participants, the entities talked about. uRole of extensive, diverse knowledge of the world. uEfficient, appropriate accessing of that knowledge. uRole of inference, to join things up. uRole of conjectured goals of the other participants in a conversation.

Further Difficulties with Language, 1 uNL expressions can be syntactically ambiguous. l She hit the man with the telescope. Does the prepositional phrase with the telescope “attach” to the man or to hit or to she?: She [ hit [[the man] with [the telescope]] ]. She [ [[hit [with the telescope]] [the man] ]. [She with [the telescope]] hit [the man]. What if the verb were “saw”?

uAnother example of syntactic ambiguity. l I saw that gasoline can explode. can: noun (N) or verb (V)? that: complementizer(CZR) or demonstrative determiner (DD) ? I saw [ [that(DD) [gasoline can(N)]] explode ]. I saw [that(CZR) [gasoline can(V) explode]].

Further Difficulties with Language, 2 uLexical ambiguity: Words often have a range of distinct meanings, possibly without varying the part of speech (noun, verb, or whatever). l ball, newspaper, bank, mole, sloth,... The different meanings may or may not be related to each other. When they are: POLYSEMY. When they’re not: HOMONYMY.

Further Difficulties with Language, 3 uWords can be vague in their meaning. l several, recently, thousands, tall, air, book [as noun], chair, think, work [as verb or noun],...

Further Difficulties with Language, 4 uSome words, such as pronouns and demonstrative determiners, are intrinsically contextual in their reference or other effects. l I, she, everyone, every, that [pronoun or determiner], the, then, today, here, and so forth.

Further Difficulties with Language, 5 uPronouns are anaphoric. But there are types of anaphor other than by pronouns, and they can get very implicit: l When John got home, he found he’d lost his key. Probably the key to his front door. He may have many other keys. l John dropped the teapot. The handle broke. What handle? None explicitly mentioned. l John went to clear the windscreen, but the de-icer can was empty. Clearing a windscreen doesn’t have to involve a de-icer can at all – the phrase the de-icer is TELLING you that some de-icer was used in the clearing as well as then REFERRING to it.

Further Difficulties with Language, 6 uWhat look like definite references may actually be indefinite or general, or may fail to refer to anything at all, or may be incorrect. l Susan’s brother is helping her. This is OK even if Susan has several brothers, at least in suitable contexts. l The dog is an intelligent mammal. This would often/normally be a statement about dogs in general. l The square root of minus one doesn’t exist. l The man in the corner actually turned out to be a woman.