This study traces two shifts in the distribution of the Spanish preposition para 'for, in order to': first, a drop in its allative uses and second, its replacement of the older preposition por 'for' with purposive infinitives. These distributional changes of the innovative para-across its own contexts of occurrence as well as in its variation with the older por-demonstrate the crosslinguistic allativeto- purposive grammaticalization path. Frequent co-occurrence of the source elements, por and a, foments their coalescence, reflected in changes in the orthographic/phonological form of the fused preposition as it loses structural analyzability. Semantic compositionality, whereby there was a discernable semantic contribution of the allative a component, is also lost as early prepositional objects designating persons decline. We find this account of the rise of para, based on gradual loss of analyzability and compositionality, to be compatible with the quantitative patterns and more insightful than an opaque and implicitly abrupt notion of reanalysis.