This paper investigates the syntax and diachrony of Italian causal clauses introduced by perché, siccome, and poiché. Although often treated as near-synonyms in Contemporary Italian, these subordinators differ systematically in their syntactic distribution, interpretive properties, and diachronic development. We show that perché introduces central adverbial clauses, merged within the vP/TP domain, whereas siccome and poiché introduce peripheral adverbial clauses, merged in the left periphery. This structural split correlates with a cluster of diagnostics: only perché-clauses can occur within the scope of matrix focus, negation, or epistemic operators, and only they can function as fragment answers. Conversely, siccome- and poiché-clauses consistently outscope matrix operators and encode non-at-issue content. A diachronic study reveals that the internal and external syntax of causal clauses introduced by each subordinator has remained stable from Old Italian to the present. However, siccome- and poiché-clauses display different semantics, as they derive from non-causal constructions (they originate from comparative and temporal clauses, respectively). We argue that the contrasting behaviors follow from the structural composition of the subordinators.
Garzonio et al. (Thu,) studied this question.