Instrument Subjects without Instrument Role

Large-scale linguistic resources that provide relational information about predicates and their arguments are indispensable tools for a wide rage of NLP applications, where the participants of a certain event expressed by a predicate need to be detected. In particular, hand-annotated corpora combining semantic and syntactic information constitute the backbone for the development of probabilistic models that automatically identify the semantic relationships conveyed by sentential constituents in text, as in the case of Semantic Role Labeling (Gildea and Jurafsky, 2002). Even if attempts of standardization of semantic role annotations are being developed (cf. the LIRICS project, Petukhova and Bunt 2008), controversial points are still present. In this paper we examine a problematic semantic role, the Instrument role, which presents differences in definition and causes problems of attribution. Particularly, it is not clear whether to assign this role to inanimate entities occurring as subjects or not. This problem is especially relevant 1- because of its treatment in practical annotation and semantic role labeling, 2- because it affects the whole definition of semantic roles. We propose that inanimate nouns denoting instruments in subject positions are not instantiations of the Instrument role, but are Cause, Agent or Theme. Ambiguities in the annotation of these cases are due to confusion between semantic roles and ontological types associated with event participants.