The third is a collection of evidence from Dutch and Swiss German (Huybregts 1976(Huybregts , 1984Shieber 1985) for the non-context-freeness of at least some natural languages.
this mode of characterization, which is subsumed by an area of research called descriptive complexity theory, is at once more declarative than an automaton or rewriting system, more flexible in terms of the primitive relations or concepts that it can provide resort to, and less wedded to the tacit, not at all unproblematic, assumption that the right way to view any language, including natural language, is as a set of strings.