An Automatic Procedure for Topic-Focus Identification

The dichotomy of topic and focus, based, in the Praguean Functional Generative Description, on the scale of communicative dynamism, is relevant not only for a possible placement of the sentence in a context, but also for its semantic interpretation. An automatic identification of topic and focus may use the input information on word order, on the systemic ordering of kinds of complementations (reflected by the underlying order of the items included in the focus), on definiteness, and on lexical semantic properties of words. An algorithm for the analysis of English sentences has been implemented and is discussed and illustrated on several examples. 1. Topic and focus in Functional Generative Description In the framework of Functional Generative Description (FGD), elaborated by the Prague research group of theoretical and computational linguistics, topic and focus are understood as constituting one of the hierarchies typical for the (underlying) syntactic structure of the sentence. A detailed discussion of this framework, including explicit definitions of the basic notions, can be found in Sgall, Haji~ov~, and Panevov~ (1986), Haji~ov~ and Sgall (1987), Sgall (1987), Petkevi~ (1987; in preparation). In the present paper it is possible only to characterize these notions briefly and informally. However, an algorithm is included that determines the topic-focus structure of the input sentences (on their nonmarginal readings). The function of this algorithm can be checked, and its usefulness, connected with that of the underlying framework, may then be compared with other approaches. In the prototypical case, the topic (theme, "given" information) can be understood as that part of the sentence structure that is being presented by the speaker as readily available in the hearer's memory, whereas the focus (comment, rheme) is what is being asserted about the topic. If negation or another "focalizer" (such as only, even, also) is present, then primarily its scope (or its "focus") is constituted just by the focus of the sentence. Thus, for example, in The king of France is not bald, the subject, which is the topic of the sentence on its preferred reading, is outside the scope of negation, so that if the sentence is uttered as referring to the world we live in, it is connected with a presupposition failure: the existence of the king of France is presupposed (entailed even by the negative sentence). Our notion of topic appears to have much in common with the more recently characterized concept of background or restrictor; on the other