Case Grammar

Dr. Fillmore has been extremely influential in the areas of syntax and lexical semantics. He was a proponent of Noam Chomsky's theory of generative grammar during its earliest transformational grammar phase. He was one of the founders of cognitive linguistics, and developed the theories of Case Grammar (Fillmore 1968), and Frame Semantics (1976). In all of his research he has illuminated the fundamental importance of semantics, and its role in motivating syntactic and morphological phenomena. Case Grammar is a system of linguistic analysis, focusing on the link between the valence, or number of subjects, objects, etc., of a verb and the grammatical context it requires. The system was created by the American linguist Charles J. Fillmore in (1968), in the context of Transformational Grammar. This theory analyzes the surface syntactic structure of sentences by studying the combination of deep cases (i.e. semantic roles) -- Agent, Object, Benefactor, Location or Instrument -- which are required by a specific verb. According to Fillmore, each verb selects a certain number of deep cases which form its case frame. Thus, a case frame describes important aspects of semantic valency, of verbs, adjectives and nouns. Case frames are subject to certain constraints, such as that a deep case can occur only once per sentence. Some of the cases are obligatory and others are optional. Obligatory cases may not be deleted, at the risk of producing ungrammatical sentences. For example, Mary gave the apples is ungrammatical in this sense.

A fundamental hypothesis of case grammar is that grammatical functions, such as subject or object, are determined by the deep, semantic valence of the verb, which finds its syntactic correlate in such grammatical categories as Subject and Object, and in grammatical cases such as Nominative, Accusative, etc. Fillmore (1968) puts forwards the following hierarchy for a universal subject selection rule:

Agent < Instrumental < Objective

That means that if the case frame of a verb contains an agent, this one is realized as the subject of an active sentence; otherwise, the deep case following the agent in the hierarchy (i.e. Instrumental) is promoted to subject.

Charles Fillmore was one of the first linguists to introduce a representation of linguistic knowledge that blurred this strong distinction between syntactic and semantic knowledge of a language. He introduced what was termed case structure grammar and this representation subsequently had considerable influence on psychologists as well as computational linguists.

The figure to the right presents the basic ideas that define a case structure grammar. Notice that linguistic knowledge is organized around verbs or more precisely, a verb sense. (A verb may have more than one sense or meaning and these are represented separately. For example, to run for office is a different sense of run than to run to first base, and these would be two different representations in a case grammar.)

Associated with each verb sense is a set of cases. Some of the cases are obligatory and others are optional. A case is obligatory if the sentence would be ungrammatical if it were omitted. For example, John gave the book is ungrammatical.

 There are two notable features that are illustrated in the example representation. First, the cases associated with a verb seem to be associated with questions that we one would naturally ask about an event. Who did what to whom when? The representation seems well adapted to the retrieval of the information provided in a sentence. This feature was particularly appealing to psychologists and computational linguists

A second interesting feature is that the same representation is provided to both the active and passive forms of the sentence. In the figure the active form is shown above the representation and the passive form below. This feature would be consistent with a finding that we rarely recall the exact syntactic form of the sentence but do recall the basic information provided by the sentence.

Another aspect of the case grammar representation is that it can be effectively used to parse incomplete or noisy sentences. For example, while John gave book is not grammatical, it is still possible to create an appropriate case grammar parse of this string of words. However, case grammar is not a particularly good representation for use in parsing sentences that involve complex syntactic constructions. The web page on representing textual information will give you some appreciation of this difficulty.