Mental mo dels and pragmatics the case of presupp ositions Guido Bo ella Rossana Damiano and Leonardo Lesmo Dipartimento di Informatica e Centro di Scienza Cognitiva Universita di Torino fguidorossanalesmogdiunitoit Keywords Mental mo dels linguistics pragmatics and presupp ositions Abstract The basic idea is that in order to understand an ut terance one must build a mental representation of the We claim mental mo dels are a framework that allows describ ed situation it is clear eg that any representa to shed light on the phenomenon of presupp ositi ons tion of arrive must include that of leave The role played A planbased lexical representation for verbs together by mental models JohnsonLaird is to provide a with the eect of conversational implicatures that dis charge p ossible mental mo dels are the key features of reasoning framework for these representations that al this prop osal lows to explain why presupp ositions survive in certain contexts For instance these representations make it p ossible to account for the fact that John didnt arrive Intro duction presupp oses John left as predicted by the pro jection of Presupp ositions are what the utterance of a sentence as presupp ositions across negation moreover this inference sumes to b e true or takes for granted They can b e is correctly mo deled as a defeasible one since it is p os triggered by dierent elements in sentences going from sible to say John didnt arrive he didnt even leave the use of denite NPs the King of France is bald pre supp oses there is a unique King of France to the pres The interpretation is carried out in the following way ence of factive verbs he regrets that he has been impolite rst of all the asp ectual features are accounted for presupp oses he has been impolite These inferences are by means of a planbased representation of the lexical characterized by resistance to negation eg he does not meaning moreover the temp oral features represented by regret that he has been impolite presupp oses he has been mental mo dels in the style of Schaeken et al as impolite and by cancellability in the presence of con well as the interpretation of the negation and of the con textual information text this amount to building one of more mental mod This pap er addresses what may b e called lexical pre els representing the describ ed event The information supp ositions In particular the event structure as de shared by all mo dels is what the sentence entails scrib ed by certain verbs allows to draw some inferences At this p oint p otential conversational implicatures are ab out the describ ed situation These verbs are classied applied their eect is to discharge those mental mo d in Beaver as signiers of actions and temp o els of the event that could have b een more precisely de ralasp ectual mo diers most verbs signifying actions scrib ed by alternative linguistic expressions In this way carry presupp ositions that the preconditions for the ac we gain more information since we are left with the tion are met Beaver page smaller set of mental mo dels presupp ositions are the We think that what accounts for preconditions for information that b ecomes shared by all these remaining the action still requires a more precise characterization mo dels Where do preconditions come from It seems rather However implicature can b e defeated in the presence vague to state that leaving is a precondition for arriv of further contextual information thus blo cking the dis ing and climbing is a precondition for reaching the top charge of mo dels presupp ositions cannot arise anymore We claim that these presupp ositions arise naturally from b ecause they do not o ccur in all event mo dels therefore a representation of the semantics of verbs in terms of ac app earing defeasible to o tions and plans describing the steps required to carry out the activity referred to by the verb It may b e observed In the following we will describ e a planbased seman that a planbased representation is complex and rather tic representation of action verbs and our treatment of exp ensive to build However we have noticed elsewhere negation and of the temp oral expression before then that it is indep endently required b oth for accounting for the conversational implicature mechanism will b e intro the meaning of communication verbs Goy and Lesmo duced Next we face the problem of the pro jection of and for the maintenance of coherence in dialogues presupp ositions Comparison with related approaches Ardissono et al and conclusions close the pap er d is not represented as a punctual event but st et John arrive as an instance of the action move that in this con prec eff sp ecializes into walk containing in its decomp o at(a)walk(j,a,n) at(n) text sition only the last steps of the plan plus the temp o ral constraints sp ecifying that b oth the whole action of ... ... step(i,l) step(m,n) walking and its last steps happ ened b efore the reference reference time time in Figure the decomp osition links are denoted by the lines connecting the walkjan token to the tokens Figure The mental mo del of John arrived to n The representing the steps On the contrary if the sentence stet line represents the event time of the action to b e interpreted were John was arriving an instance would b e built where the reference time o ccurs within the sequence of steps that conclude the action In b oth A planbased representation of verbs cases the steps preceding the nal sequence are not rep We will mainly consider verbs denoting actions that resented but are assumed to exist on the basis of the are intentionally executed by an agent The meaning action instance inner relations and can b e consequently of these verbs is represented by action schemata that added to the representation if they b ecome relevant Ac describ e how actions are carried out by a sequence of cording to this representation the mental mo del of John steps When a sentence is interpreted an action in arrived entails the mo del of John left where in turn the stance is built on the basis of the schema corresp ond initial steps of the action walk are constrained to precede ing to the main verb then a set of constraints express the reference time ing the temp oral and asp ectual information conveyed by Therefore the presupp osition John left is not conned the other linguistic elements asp ectual predicates ad to a separate set of prop ositions that must b e accom verbials verb arguments and so on is added to this rep mo dated in the representation as in Van Der Sandt resentation by means of conditionaction rules Bo ella moreover the requirement is satised that and Damiano Temp oral constraints refer to the presupp ositions are in some sense inserted at the o ccurrence of the action instance with resp ect to sp eech b eginning of the sentence interpretation Beaver time and reference time following a reichenbachian tem and not added or calculated afterwards as p oral reference schema in Karttunen Gazdar b An action schema Act is comp osed of arguments among On the other hand we do not face here the problem of which the agent agt Act and the start and end time the anaphorical character of presupp ositions exempli of the action stAct and etAct resp ectively denot ed in he left an hour ago but he didnt arrive where the ing temp oral p oints the preconditions and eects of the two clauses refer to two phases of the same underlying action and the action decomp osition b o dyAct com action of walking p osed of steps the start and end time of the steps can b e sp ecied to o The representation of negation Usually a mental mo del representing an action do es We have adopted a p eculiar treatment of nega not contain all the step instances tokens of the plan tion in order to account for the fact that the but only a subset of them Since steps express the fo negated event was somehow exp ected to happ en cused part of the action and its temp oral placement only We interpret such exp ectations by representing them the steps must b e included that are needed to represent in terms of intentions attributed to the involved the constraints resulting from the interpretation The agent mental mo dels containing unexecuted action in remaining steps can b e later inferred and added to the stances can b e readily interpreted as an agents men representation if they b ecome necessary for reasoning tal description of another agents intentional state purp oses Moreover action schemata can b e only par Bratman et al tially instantiated to account for the fact that linguistic The representation of John did not arrive includes the expressions describ e an event by highlighting only cer related plan instance of walking and its decomp osition tain features of its that the sp eaker considers relevant into steps the negation is not represented by lab eling to his goals In our approach this corresp onds to build the last steps in the plan instance as denied as men ing mo dels in which only the currently relevant steps are tal mo del theory prescrib es JohnsonLaird On represented in order to fo cus on a sp ecic phase of the the contrary starting from the premise that the walking action or to represent the fact that the action has b een 1 action did not end b efore the reference time R all the only partially executed representations that include the plan instance act and For example the interpretation of John walked to the satisfy the constraint etact R are allowed Note that store contains only the rst and the last steps of the plan 1 and constrains them to precede the reference time here Otherwise