Do we need summary and sequential scanning in (Cognitive) grammar?

Cognitive Grammar postulates two modes of cognitive processing for the structuring of complex scenes, summary scanning and sequential scanning. Generally speaking, the theory is committed to basing grammatical concepts upon more general cognitive principles. In the case of summary and sequential scanning, independent evidence is lacking, but Langacker argues that the distinction should nonetheless be accepted as it buys us considerable theory-internal explanatory power. For example, dynamic prepositions, to-infinitives and participles (e.g., into, to enter, entered) are distinguished from finite and bare verbs in terms of summary vs. sequential scanning. In this paper, we try to show that various theory-internal and theory-external arguments do not seem to support the two scanning modes. In particular, we offer a detailed examination of causatives (e.g., get, make) and argue that their complementation patterns are difficult to reconcile with differences in scanning. We conclude that the status of, and need for, summary and sequential scanning in (Cognitive) grammar is doubtful, especially if grammar is approached from the viewpoint of the language learner/user. It follows also that the parcelling of some form-function mappings may prove less clear-cut than previously assumed.