Abstract The present paper investigates the phenomenon of “inflected complementizers” seen in many Continental West Germanic dialects. The proposal developed takes as its point of departure the commonality of linear distribution between inflected complementizers and finite verbs that exhibit the same kind of special morphology. This commonality manifests itself in implicational relationships, which strongly suggest that the behavior of complementizers is an analogical extension of morphological mergers involving finite verbs in the same linear position. Under this analysis, the occurrence of inflectional markings on wh-phrases in embedded complementizer-less questions and relative clauses can be seen as a straightforward extension of the same mechanism. We further propose a concrete implementation of this proposal in Head-Driven Phrase Structure Grammar, which builds on Zwicky's distinction between morphological FORM and SHAPE. Finally, we argue that the approach based on analogical extensions of shape alternations is better suited to motivate the emergence of the phenomenon than current proposals that assume a universal agreement relationship between complementizers and subjects, regardless of whether that agreement relations is overtly manifested.