From: AAAI Technical Report WS-96-03. Compilation copyright © 1996, AAAI (www.aaai.org). All rights reserved. The believability of Road Runner cartoons: logical consistency conquers unreality Robert McCartney Michael Anderson Dept of Computer Science and Engineering Computer Science Department University of Connecticut University of Hartford Storrs, CT 06269 West Hartford, CT 06117 [email protected] [email protected] .edu The rules and disciplines are properly difficult to to entertain, and hypothesize that this effectiveness is identify. But there are--there must be--rules. due in part to a believable environment populated by Without them, comedy slops over at the edges. actors with recognizable motivations. Identity is lost. The structure of this paper is as follows. We dis- -Chuck Jones cuss how Road Runner and Coyote world is an amal- gam of features from the real world, other commonly Abstract used cartoon features, and particular more specific fea- Entertainmenthas always involved fictional characters tures having to do with the Coyote’s beliefs. Next, we in artificial settings. Effective use of artificial worlds present a set of logical axioms designed to support for- and characters demandsthat the agents and worlds be mal commonsensereasoning in this world-if a world is believable and understandable. Weexamine the world logically consistent, we should be able to formalize its and characters in the RoadRunner cartoons, and show commonsense underpinnings in ways similar to those howthe world, whilenot realistic, is internally consis- used for commonsensereasoning about the real world. tent. Weargue that the consistency of both the world Next, we use these axioms in an example proof that the andthe actions of the agents relative to their motiva- logical formalization supports; in particular we present tions are importantfactors in the success of the series, and provide a model for developing believable agents a proof that would not hold in the real world. Fi- andworlds in general. nally, we consider howthe creators of this world used an alternative mechanism(a set of rules) to keep logi- cal consistency, and argue that this logical consistency Introduction contributes muchto the entertainment value. Drama and comedy have a long history as human en- tertainment, with an oral tradition that predates writ- The world of Road Runner and Coyote ten history in those cultures that predate written his- As drama, the Road Runner-Coyote cartoons are quite tory. The meaning of such performances, whether for simple: entertainment, affirming cultural values, or challeng- ing the status quo, depends to some degree on the be- ¯ only two characters are involved, lievability of the characters and their situations. The ¯ there is no dialogue, characters need not be human, and the environment in which they act need not be earth, but the actions and ¯ the interaction between characters is simply one of situations must seem reasonable in the context of the pursuit and avoidance, environment. ¯ the environment is consistent and minimal, and In this paper, we consider the artificial world pre- sented in the Road Runner and Coyote Cartoons, ¯ the theme is persistent across the entire series. forty-two of which were produced between 1949 and The environment of the Road Runner-Coyote car- 1980 [Beck, 1989] 1 While the world presented in these toons is an idealization of the southwest American cartoons seems quite unrealistic, most actions within desert: rugged terrain, with few plants (other than this world are quite predictable, and the unpredictable cactus), wires strung on poles, and lots of two-lane ones, largely those that are funny, seem reasonable in highway. These roads play a central part in this world, the context of the cartoons. We present this world as since the Road Runner spends his time traveling along an exampleof an artificial world that is effectively used them, and the improbable concentration of bridges, 1A 43rd cartoon, Chariots of Fur was released late in tunnels, and roads cut into cliffs makes for an inter- 1994. This world has also been used, with less success, in esting environment for the Coyote to try various ploys advertising automobilesand soft drinks. to catch the Road Runner. The theme: the Coyote (Eatibus Almost Anythin- RRC.17. occurs(/,fall(A)) gus) is hungry and sees the Road Runner (Tastyus Su- knows(A, -~3y personicus) as his only chance for a decent meal but true_in(start(1),support(Y, A)),start(I)) the Road Runner is too fast for the Coyote simply to (Toonville Clichd I: Agent A will only fall if A knows chase and catch. His only chance is somehowto trap that nothing supports A.) the RoadRunner and, for the duration of the series, his RRC.18. occurs(/,burn(A)) planning and scheming bring him pain, suffering, and knows(A,true_in(start (I), burning(A)),start indignity ... but no Road Runner! The Road Runner (Toonville Clichg II: Agent A will only suffer the pain spends his days, appropriately, merrily running along of burning when A knows that A is burning.) the road and has little interest in the Coyote and his doings. His sole contribution to the affair is a few well- RRC.19. (occurs(I,make(coyote,X)) placed "beep-beeps" that startle the Coyote into com- A believes(coyote, trueAn(end(I), representation( promising positions. X, O, B)), end(I))) While many things in the environment have real- true_in(end(I),instance(X, world analogs, other features are typical of cartoons-- (Coyote’s DilemmaI: If Coyote believes something he a commonclich~ is a character whowalks off a cliff or made is a representation then it is an instance of that steps out of a windowto not fall toward the ground type.) until he notices that he is not supported by anything, RRC.20. or a character whodoes not feel pain when set on fire believes(coyote, true_in(S2,instance(X, O)), $2) until he sees that he is burning. The abstraction here lieves(coyote, true_in(S1, representation(X, O, B)), seems to be that physics is affected by the knowledge 5’1) A precedes(S1, $2)) or belief of the involved characters. This notion is very true_in(S2,representation(X,O,B)) commonin these cartoons, where much of what hap- (Coyote’s Dilemma II: If Coyote believes that some- pens seems to depend on the beliefs and intentions of thing is an instance, and he previously believed it to be the Coyote. a representation, then it is a representation.) If this world is believable and understandable, it should be describable by some set of axioms, as has Figure 1: Axioms pertaining to belief and state been done for commonsense reasoning about things changes in the world. The differences between this world and the real world complicate the job of axiomatizing this world, but such an axiomatzation provides evidence a sign. When the Road Runner zips by the sign and that the world is in general logically consistent, and trap without even looking at it, the Coyote is stupe- the efforts could lead to a greater understanding of the fied. In a few moments, the Road Runner returns to sorts of differences that an artificial world might ex- the scene sporting a sign that reads "Road Runners hibit without becoming too alien to be understood. Can’t Read!" This statement is close to the classic liar sentence "This sentence is false." Howcan the Road Road Runner-Coyote according to Runner be using written language if he can not read formal logic it? The basis for the axiomatization of the Road Runner A number of sorts are defined to constrain portions - Coyote Microworld is sorted modal temporal logic of the logic to pertain to only certain groups of entities. [Davis90]. Included in the axiomatization are a num- Sorted predicates include state and event predicates, ber of necessary modal belief and knowledge axioms interval predicates, and domain dependent predicates and axioms required for reasoning about the physical that are true or false independently of situations. The objects used by the Coyote in his never-ending quest predicate true_in(S,T) where state fluent T holds of Road Runner Tartare. The axiomatization of this situation S functions as the state predicate. The pred- microworld is to the end of proving that, no matter icate occurs(I,E) where event type E occurs in interval what situation they find themselves in, the Coyote will I functions as the event predicate. Various states and never catch the Road Runner. events are defined that hold in certain situations and The approach taken by the current work is to axiom- are used as arguments to the true-in and occurs pred- atize a subset of situations that are portrayed in the icates. Standard interval predicates are also defined series of cartoons such that an interesting set of ax- [Allen83]. ioms can be developed. Further, this set of situations Agents’ beliefs, knowledge and goals are repre- has been chosen such that inconsistent and anomalous sented as modal operators with a temporal dimension. situations are avoided, allowing for a simpler, consis- These operators include: believes(A,¢,S) where agent tent set of axioms. This is a necessary tack because A believes statement ¢ in situation S, knows(A,¢,S) not all behavior in this microworldis logically consis- where agent A knows statement ¢ in situation S, tent. For example, at least once the Coyote sets up a and goal(A,¢,S) where agent A has goal ¢ in situa- trap that requires the Road Runner to stop and read tion S. Three axioms - Arrogance of Belief (RRC.5), 0 ! 993 W~nerCommunications Figure 2: The painted tunnel ploy. Knowledgeis Belief (RRC.6), Arrogance of Knowledge tity X is simply a representation (painting, drawing) (RRC.7) - are used to define the relationships between of type O (tunnel, bridge) and exists on substrate belief, knowledge, and actual fact [Davis90].