-- The Grammaticization of Zero Asymmetries in Tense and Aspect Systems Joan Bybee University of New Mexico 0. Introduction An interesting consequence of the grammaticization process is the develop­ ment of meaning in zero-marked forms. When a grammaticizing overt mor­ pheme becomes obligatory, it may happen that other meanings within the same functional domain, which previously had no grammatical expression, come to be expressed by a meaningful zero. In this paper I will describe a possible inferential mechanism by which meaning may develop in grammat­ ical morphemes ( = grams) with no overt expression. I will also examine the nature of the meaning of zero grams, arguing that such forms have positive semantic content, which arises from the communicative context. In addi­ tion, I will discuss the distribution of zero grams in the tense/aspect systems of a seventy-six language sample, focussing primarily on the fact that zeroes have a very different distribution among the aspects of the present tense versus the past tense . 1 I will argue that the different grammaticization of overt and zero grams in the present and past tense is due to the distinct functions of discourse formulated in the present versus the past tenses. 1. The conceptual domain of grammatical tense and aspect Recent cross-linguistic studies of tense and aspect (Comrie 1976,1985; Bybee 1985; Dahl 1985 and Bybee & Dahl 1989) establish that perfective and imperfective are the most general and the most common senses expres­ sed grammatically in verbal systems in the languages of the world. Perfec- 236 Joan L. Bybee The Grammaticization of Zero 237 tive aspect can be characterized as viewing the situation (expressed by the predicate) as a bounded unit. The imperfective does not take the situation with present and past tense only distinguished in the imperfective aspect, as for example in Spanish and French. See (5). to be bounded, but rather views it as having some sort of internal structure. (5) While some might want to view the imperfective as expressing the lack of ASPECT perfectivity, I would argue here (as well as elsewhere, Bybee et al., in press) that the imperfective also has positive semantic content, and in fact can be subdivided into several different senses, which can have their own PERFE~CTIVE means of expression in some languages. (P«I.,ile) A For dynamic verbs the most common sub-senses of imperfective are the progressive and habitual. The progressive takes a situation to be PRESENT PAST actively ongoing at reference time, while an habitual situation is one which (Present) (Imperfect) is customarily repeated on different occasions, and a5 Comrie (1976) puts it, is characteristic of an extended period of time. Both progressive and Aspect is hierarchically higher than tense in this diagram, according to habitual can be used in either the present or past tense, as the following Dahl, because it is much more common for present and past imperfective to English examples show.2 have similar expression than past imperfective and perfective. Further, Bybee (1985) argues that aspect is more relevant to the verb than tense is. (1) Malcolm is washing dishes. (present progressive) Despite the proposal that aspect is in a sense more basic than tense, the dis­ (2) Malcolm was washing dishes. (past progressive) cussion in this paper examines the present and past tenses in terms of the (3) Malcolm washes dishes. (present habitual) aspects which may be expressed in each one. Thus we see that present tense (4) Malcolm used to wash dishes. (past habitual) is inherently imperfective, so that a general present which includes both Given the perfective on the one hand, and the imperfective, divisible into progressive and habitual could be called a 'present imperfective'. progressive and habitual, on the other, our interest here is in the asymmet­ Besides progressive and habitual in the present tense we also have ries inherent in the way these senses cross-classify with present and past generic statements. I would argue that habitual and generic are aspectually tense. The first basic asymmetry lies in the fact that for most verbs there is the same, and that the main difference between habitual and generic sen­ no perfective aspect for the present tense. If perfective views a situation as tences has to do with the nature of the subject, as can be seen in (6) and (7), having temporal boundaries (Comrie 1976), then for most verbs there can where the aspectual interpretation of the verb is essentially the same. be no "present perfective", since a situation being presented as in effect at (6) Dogs pant to cool off. the moment of speech cannot at the same time be presented as bounded. (7) My dog pants to cool off. An interesting exception to this, which illustrates the nature of a present perfective, can be found in present tense performative use of performative This hypothesis is supported by the fact that no clear distinction in the verbs (Dahl 1985: 81). The utterance "I bid three spades" is in itself a present expression of present habitual and generic emerges in a cross-linguistic sur­ bounded situation. Another similar class of present perfective functions vey of verbal categories in seventy-six languages (the Gramcats Project, to occur in the narration of ongoing events, such as in sports commentary ("he be described in more detail below). In this survey of reference grammars, kicks the ball, it misses the goal..."). However, for most verb classes and we studied the meaning of all grams fixed in position with respect to the most discourse contexts, the present tense consists of the imperfective verb. While the expression of generic meaning is not commonly mentioned aspects of progressive and habitual, and the perfective is restricted to the in reference grammars, the instances we found of explicit mention or past tense. (See also Comrie 1976:82-3.) exemplification of generic meaning showed that in ten out of eleven cases it Thus Dahl (1985) argues that inflectional aspect systems (unlike the is expressed by a form that could also express habitual meaning. Given no derivational ones of Slavic languages) most often are of a tripartite nature, real aspectual difference between habitual imd generic, the term habitual will be used here to cover the aspectual sense in both types of sentences. 238 Joan L. Bybee The Grammaticization of Zero 239 For stative predicates, no distinction can be made between progressive and habitual. One could argue that a stative situation such as he is tall or she characterizes my general or habitual choice of beverages. It cannot be used knows the answer is both habitual and progressive, that is, in progress at to indicate that I am now (or shortly to be) engaged in drinking a specific reference time, and also characteristic of an extended period of time. Or, cup of coffee, as the semantic anomaly of (9) shows: one could think of progressive and habitual as applicable only to dynamic (9) *I drink a cup of decaf right now. situations and argue that they are simply not relevant to stative predicates. Rather, with dynamic predicates, it is obligatory that ongoing activities be The latter view is more compatible with the grammaticization paths of pro­ described in the progressive: gressive and habitual, since the meanings of both are initially only applica­ ble to dynamic predicates. In either case, however, statives interact differ­ ( 10) I am drinking a cup of decaf right now. ently with imperfective aspect, being neutral to the distinction between The fact that the Simple Present is now incompatible with temporal phrases habitual and progressive. The major semantic distinctions applicable to sta­ such as "right now" attests to the fact that it is explicitly expressing habitual tives are being in a state versus entering into a state, and present versus meaning. The lack of a tense or aspect marker in the verb phrase conveys past) We will return in section 9 to a study of the various ways that stative this particular meaning. 4 predicates can interact with perfective aspect. In contrast, consider the Past Habitual periphrasis that is commonly With this sketch of the senses covered by aspect in the present and past used in English, used to. While this periphrasis is quite frequent in the past, tense established, we now turn to a discussion of the way in which zero it has not become obligatory. The evidence for this is the fact that the Sim­ grams become meaningful. ple Past is compatible with temporal phrases that indicate habitual situa­ tions. Thus (II) and (12) have nearly the same meaning: ( li) She sang to him every day. 2. Obligatoriness and zero markers (I2) She used to sing to him every day. The evolution of lexical material into grammatical material is a long and If used to had become obligatory, then the Simple Past would be restricted gradual process, beginning with the occasional use of a periphrastic con­ to non-habitual meaning. (And since the Past Progressive is obligatory, if struction which gradually becomes more and more frequent. The develop­ used to became obligatory, the Simple Past would have the meaning of per­ ing gram, as it increases in frequency, loses specific semantic features, fective.) At present it is not so restricted, but can be used for single com­ thereby becoming more general in meaning, while at the same time becom­ pleted actions as well as habitual situations. Note that the Simple Past has ing more rigidly fixed in syntactic position. During the course of develop­ an overt marker for tense - in the suffix or stem change - but if the Past ment a gram may also become obligatory. Not all grammatical morphemes Habitual were to become obligatory, then we would describe the Simple Past as having a zero marker for aspect.