Assessing Parsimony in Models of Aspect

Assessing Parsimony in Models of Aspect Damien Munch (munch@telecom paristech.fr) Jean-Louis Dessalles (dessalles@telecom-paristech.fr) Telecom ParisTech, 46 rue Barrault, F-75013 Paris, France Abstract Though human beings are experts in the determination of aspectual relations, current models of Aspect lack principled parsimony. We show that even on a limited segment of language, determining aspectual interpretations seems to require much ad hoc information. Our suggestion is to give parsimony first priority. The model we present in this paper is limited in scope, but its complexity is bounded in principle. Keywords: Temporal Aspect; Cognitive minimalism; Natural Language Processing. Aspect and Parsimony Human beings have strong intuitions about Aspect. For instance, though the two following sentences are syntactically well-formed, only the first one is semantically acceptable. She wants to eat up the cake in one minute. # She wants to eat up the cake for one minute. Principled vs. Actual Parsimony These intuitions suggest that native speakers of a given language have a genuine competence concerning Aspect. Aspect combines different features, such as termination or repetition. It is tempting to consider this “aspectual competence” as consisting in a mere pattern-matching process. For instance, some incompatible features such as boundedness and unboundedness would be assigned to “to eat up the cake” and to “for one minute” respectively, making their combination illegal in (2). Unfortunately, no pure pattern-matching model of Aspect has been discovered yet. All models include computational components consisting in exceptions, type change (coercion) or context- dependent procedural rules. For instance, the sequence of instructions shown in Figure 1 has been proposed by Gosselin (1996) to describe the behavior of the French equivalent of ‘in’ + duration (as in example (1)). (a) (b) (c) (d) (e) that expand Reichenbach’s (1947) reference point system; these intervals may coincide, overlap or be in various inclusion relations. The whole system produces many potential combinations, but only a few of them are useful to represent aspectual meanings. The problem with computational models is that they may uncontrollably depart from parsimony. For instance, Gosselin’s model sets no limit to the size of the instruction set that may be assigned to a given word combination. The present paper has three related objectives. First, our aim is to highlight the necessity of limiting the complexity of models of Aspect, while making the distinction between actual and principled parsimony. Second, we will propose a small benchmark on which the parsimony of models of Aspects may be compared. Third, we will evaluate our own model in regard to this benchmark and discuss the results. construct an interval [ct1, ct2] make it non-punctual (ct1 < ct2) make it coincide with the process interval make the process interval ‘intrinsic’ include it into the ‘reference’ interval Any model of Aspect must face the difficulty of describing a variety of sentence types that sometimes differ in minute details. Several authors tried to discover notions that prove useful to explain aspectual variation. The best known conceptual framework in this respect is probably Vendler’s (1967) categorization of the lexical Aspect of verbs (state, activity, accomplishment, achievement). Certain notions such as dynamicity or perfectivity have been explored by various authors (e.g. Comrie, 1976; Gosselin, 1996; Smith, 1997). Elucidating the way human beings process Aspect would be easy if the only problem was to check the compatibility of fixed features attached to lexical entries or to predicates, such as ‘activity’, ‘dynamicity’ or ‘telicity’. Unfortunately, mere feature unification proves insufficient to predict the aspectual acceptability of sentences. For instance, ‘drink a glass of wine’ is expected to clash with ‘for three years’, because the former is perfective and the latter is durative. The sentence: Figure 1: Instructions representing en + duration (after Gosselin,1996). Another sequence of instructions is needed for ‘in’ + period (as in “in 2010”). Gosselin proposes a variety of “programs” like this one to account for aspectual words. Each step of these programs has several alternatives. For instance, Gosselin’s model introduces four interval types She drank a glass of wine for three years is however acceptable with an iterative interpretation (‘She drank a glass of wine everyday for three years’). The sentence is ‘saved’ dynamically, thanks to a phenomenon called ‘coercion’ (de Swart, 1998) or ‘conflict resolution’ (Gosselin, 1996): iteration transforms a perfective situation (‘drink a glass of wine’) into an imperfective repeated situation that matches ‘for three years’. Though the introduction of procedural components like coercion seems inevitable, it introduces a risk. If the language in which procedures are expressed is too rich, the model is no longer constraining. When it reaches the