Thematic Roles (or Theta-Roles) are theoretical constructs that account for a variety of well known empirical facts, which are more or less clearly delimited. In other words, Theta-Roles are not directly observable, but they do have empirical content that is open to empirical observation. The objective of the present paper is to sketch the nature and content of Theta-Roles, distinguishing their universal foundation as part of the language faculty, their language particular realization, which depends on the conditions of individual languages, and idiosyncratic properties, determined by specific information of individual lexical items.According to general agreement, including traditions of various sorts, the properties Theta-Roles are to account for have to do with the morpho-syntactic realization of semantic relations between parts of complex linguistic expressions. A rather simple case in point is given in (1), where the relation between Brecht, Villon and adaptation in (a) is semantically parallel to that between the corresponding elements in the morpho-syntactically different verbal construction (b):Theta-Roles have to account for the parallel properties as well as the differences of these relations. For general reasons, the underlying theoretical framework must meet the usual conditions of parsimony and adequacy, where (A) Parsimony requires stipulations to be minimized, and (B) Adequacy requires all relevant empirical facts to be taken into account.According (A), the theory of Theta-Roles must not set up principles or entities that follow from independently motivated theoretical assumptions, according to (B) it has to capture semantic, syntactic, morphological, and other phenomena that are related to Thematic Roles, a requirement that is clearly in need of clarification, as there is no simple and a priori delimitation of the phenomena to be included. Some preparatory observations might be helpful in this respect.
Five Basic Observations(I) Interface Character: The correspondence between semantic relations and morpho-syntactic properties is not necessarily simple and uniform. Thus, the same semantic properties might be realized by different formal means, a shown in (1), and the same formal means might realize different semantic relations, as illustrated in (2), where the recipient of anziehen (dress) shows up as direct object seinen Sohn in (a) and as indirect object seinem Sohn, marked by the oblique Case in (c), while the direct object den Mantel realizes the object of the action in (b) as well as (c):(2)(a) Peter zieht seinen Sohn an (Peter dresses his son) (b) Peter zieht einen Mantel an (Peter puts a coat on) (c) Peter zieht seinem Sohn einen Mantel an (Peter helps his son to put a coat on)