Journal of Historical Syntax

Alberto Frasson. This paper examines the diachronic development and synchronic distribution of the Serbian form 'kako' (’how’), showing that its interrogative and declarative uses derive from a single inherited composite structure. Drawing on data from Old Serbian texts spanning the twelfth to the eighteenth century, I distinguish two major functions: interrogative 'kako', a manner adverb that participates in regular wh-movement, and declarative 'kako', a complementizer introducing propositional, eventive and irrealis subordinate clauses. I argue that 'kako' originates from a Common Slavic phrasal configuration consisting of a wh-element k- and a manner nominal WAY, whose internal structure became opaque over time. Diachronic evidence shows a gradual increase in the use of 'kako' as a complementizer, accompanied by semantic bleaching, loss of interrogative features, and structural reanalysis in line with syntactic economy principles. A comparison with Romance, particularly the divergent developments of Latin 'quomodo', Friulian 'cemût che' and Salentino 'cu', provides an independent model for understanding how a composite wh-expression can undergo grammaticalization into a C-head. The Serbian data thus offer a well-attested case of a wh-expression grammaticalizing into a multifunctional complementizer, illustrating cross-linguistic pathways between interrogative syntax and complementizer systems.