This study argues that constructions of purpose, reason and intended endpoint have a special status in typologies of complex sentences, because they combine features of the adverbial domain and the complement domain. The feature they share with adverbial clauses is that they do not function as the object of the predicate of the main clause, but instead elaborate on its circumstances. The feature they share with complement clauses is that unlike other adverbial clauses they specify; the mental state of some participant in the main clause, typically the agent. Evidence for this special status comes from two sources. On the one hand, it is shown that the recognition of a mental state relation is necessary in semantic terms, to distinguish the three constructions from? semantically similar types in the adverbial domain, and to explain their exceptional behavior in terms of presupposition. On the other hand, it is also shown that the presence of such a mental state relation is crosslinguistically reflected in the formal make-up of the three construction types, specifically in the use of mood markers in the dependent clause, and in the use of conjunctions that are shared with the domain of represented speech. From a theoretical perspective, the intermediate status of Constructions of put-pose, reason and intended endpoint is important because it provides structural evidence for layered models of clause structure, specifically for the distinction between a description-related and an interaction-related layer of organization, and for a further subdivision of the interaction-related layer in terms of modal and illocutionary features.