Secondary grammaticalization in clause combining: from adverbial subordination to complementation in English

•Some adverbial subordinators develop a complementizer function over time.•Minor declarative complementizers are associated with subjectivity and irreality.•This development represents a case of secondary grammaticalization (gzn).•Gzn takes place at the level of clause links: adverbial link > complementizer.•Gzn also takes place at the level of clause combining: hypotaxis > subordination.

In this article we look at a case of secondary grammaticalization in English which entails the development of originally adverbial subordinators into complement-clause connectives. The study systematizes our earlier findings regarding the adverbial links but, if, though, lest, as if, as though, and like, which over time have come to realize a subsidiary function as equivalents (or near-equivalents) of the major declarative complementizers that and zero in certain specific contexts. We show that minor declarative complementizers are typically associated with the expression of subjectivity and irreality. As such, they are usually attested in complementation structures in which subjectivity is also at hand (e.g. they are complements to specific predicate-types occurring in non-assertive environments). The development discussed here illustrates grammaticalization both at the level of clause links and at the level of clause-combining.