Constituent structure is considered to be the very foundation of linguistic competence and often considered to be innate, yet we show here that it is derivable from the domain-general processes of chunking and categorization. Using modern and diachronic corpus data, we show that the facts support a view of constituent structure as gradient (as would follow from its source in chunking and categorization) and subject to gradual changes over time. Usage factors (i.e., repetition) and semantic factors both influence chunking and categorization and, therefore, influence constituent structure. We take as our example the complex prepositions of English, for instance, "on top of," "in back of," and "in spite of," whose internal constituent structure has been much debated. From observing strong (but not absolute) usage trends in the corpus data, we find that these complex preposition sequences display varying degrees of emerging constituency. We conclude that constituent reanalysis, like language change generally, proceeds gradually.