THETA THEORY

THETA THEORY

Theta theory is concerned with the assignment of an argument structure to a sentence. A verb has a number of the thematic (or ‘theta’) roles that must be assigned to its arguments, e.g. a transitive verb has one theta role to ‘discharge’ that must be assigned to an NP (Noun Phrase).

The easiest method of obtaining and applying theta probabilities will be with reference to whole theta grids. Each theta grid for a word will be assigned a probability that is not dependent on any particular items in the grid, but rather on the occurrence of the theta grid as a whole.

A preliminary version of the Penn Treebank bracketed corpus was analysed to extract information on the sisters of particular verbs. Although the Penn Treebank data is unreliable since it does not always distinguish complements from adjuncts (an adverb or a phrase that adds meaning to the verb in a sentence or part of a sentence), it was the only suitable parsed corpus to which the authors had access. Although the distinction between complements and adjuncts is a theoretically interesting one, the process of determining which constructions fill which functional roles in the analysis of real text often creates a number of problems.

Well beyond the framework of generative grammar, a central question of linguistic research is whether, or how, certain aspects of meaning influence the form of a sentence. It is assumed that a verb is lexically associated with information that determines, at least in part, the predicate-argument structures it can appear in. The lexical approach raises a set of basic questions. First, there is a properties problem: which kind of lexical information enters into the determination of argument structure? Second, there is an interface problem: how are the relevant chunks of information encoded, such that they are accessible to both general cognition, and the derivation of syntactic predicate-argument structures? Third, there is a mapping problem: how exactly are lexical-semantic properties translated into grammatical functions?

Every verb classifies the participants in the event, state, or process it denotes with respect to the cognitive domain in which it is to be interpreted, and it specifies whether the event participant is an agent or a patient in that domain. The Theta System thus derives exactly eight thematic roles as clusters.

The properties problem and the interface problem
The grammatically relevant property of verb meaning is agency in two crucial domains of cognitive event interpretation, folk physics and folk psychology. Encoded as clusters of binary features, this information is accessible in grammatical derivations by hypothesis. The third question regarding the mapping of lexical semantic information on syntactic functions is addressed on the basis of German data in chapters two, three and four. Chapter two lays the empirical basis with a detailed description of a set of German verbs. The chapter first develops the routines that allow us to postulate specific role-clusters for a given verb, and then establishes generalizations about the relation between role configurations and corresponding predicate-argument structures, including diathesis alternations. The overall conclusion is that Reinhart’s (2000, 2002) theory is accurate in most cases.

Although the generalizations of the Theta System are robust and most probably universal, they are by no means exhaustive. A number of non-semantic factors enter into the determination of syntactic structures, in particular morpho-phonology, and purely syntactic requirements like structural case. Objects of prosodic structure are interpreted by a mapping into syntax, and objects of syntactic structure are interpreted by a mapping into semantics. The relation between lexicon (all the words and phrases used and known by a particular person or group of people) and grammar is not an interface in this technical sense. It is assumed with Chomsky (1995) that a lexical item enters a grammatical derivation together with all of its features by being selected into an initial array.

Once a lexical item has been selected into an initial array, its features no longer form an unanalyzable unit. Generalizations over argument-linking are formulated in terms of merging instructions for thematic role-clusters. In general, the thematic roles provided by a lexical verb-entry merge with syntactic heads of category [/-N], and they are assigned to [/-V]. In particular, a [+] cluster must merge with the head v (which introduces external arguments), and the fully specified cluster must merge with V. No reference to arguments needs to be made in these merging instructions.

It is possible to make explicit generalizations on how the perception of predicate-argument relations determines the projection of syntactic argument structure, but no recursive, pre-syntactic system of event-representation is needed to do that. With the constructional approach, the present theory shares the assumption that a noun phrase can only receive an argument-interpretation, if it appears in a specific syntactic configuration. It sharply differs from the constructional approach in that it explains why and how the È role-assigning potential of any given construction depends on the lexical entries, from which it is projected.

THETA-THEORY REVIEW NOTES

1. As part of their lexical entry, verbs, and other content lexical categories, have an argument structure that can be viewed as a type of syntactically relevant semantic information.
2. The argument structure is simply a list of the theta-roles (or thematic-roles) realized by some argument.
3. An argument is an NP or S. All S-complements are arguments. All NPs, except pleonastic elements it & there, are arguments. Generally speaking, an argument is NP or S with semantic content.
4. There is a tight one-to-one correspondence between theta-roles and arguments. This is clearly specified in the Theta-criterion, the most important element of theta-theory: Theta-criterion: Every theta-role is assigned to one and only one argument. Every argument is assigned one and only one theta-role.

A theta-role is assigned both to a syntactic position & to the argument that occupies that position. A theta-position, then, is simply a position to which a theta-role is assigned.
The paradigmatic theta-positions are as follows:
a. Object position of a transitive verb in active voice:
... V'
/ \
Vtr NP
b. Subject position of a VP that is headed by a V with a "verber"
theta-role to assign (with external theta-role):
... S
/ \
NP VP

V
c. Object position of a preposition with semantic content:
... PP
/ \
P NP

(Rishi Kumar Nagar, Jalandhar)