This paper reports on the results of an investigation into the semantics of verbs and idiomatic expressions that take non-nominative (quirky) subjects in Icelandic. It is shown that subject case in Icelandic is semantically predictable to some degree. The basic generalizations are as follows: Nominative subjects are thematically unrestricted in that they can be Agents, Patients, Themes, Goals or Experiencers.

By contrast, quirky subjects are never Agents in Icelandic even if the term is understood in a broad sense (including instruments, natural forces, causes, etc.). Moreover, an accusative subject cannot be a Goal and some subclasses of Experiencer verbs never have accusative subjects.

The paper also advances the hypothesis that lexical case on subjects in Icelandic should be split into thematic case and idiosyncratic case (where dative Goals and Experiencers are thematic but dative Themes and Patients and accusative subjects are idiosyncratic). This distinction is supported by the fact that idiosyncratic case on subjects is in the process of getting lost whereas thematic case is gaining ground, as witnessed by the tendency of accusative Experiencer subjects to become dative (socalled Dative Sickness) and quirky Patients and Themes to become nominative.

A further argument for this distinction comes from the ‘middle’ suffix -st. This suffix is commonly found on verbs whose dative subject is an Experiencer or Goal but never on verbs with accusative subjects or dative subjects that are Patients or Themes. Thus, the suffix -st is incompatible with idiosyncratic case on subjects and similar facts also hold of idiomatic expressions.