Language Diffusion and Contact Zones

Geographers distinguish two broad mechanisms by which a cultural trait such as a language spreads across space: relocation diffusion, in which the trait moves because its speakers physically migrate, and expansion diffusion, in which the trait spreads outward from its origin while also remaining, and often strengthening, at that origin. The Swedish geographer Torsten Hägerstrand, in his 1953 study of agricultural innovation adoption in Sweden, further divided expansion diffusion into contagious diffusion, which spreads through direct contact between neighboring individuals rather like a contagious disease, hierarchical diffusion, which jumps between large population centers before filtering down to smaller towns, and stimulus diffusion, in which only the underlying idea, rather than the specific trait itself, is transmitted and then locally reinvented. Spanish and Portuguese in the Americas illustrate relocation diffusion driven by colonization after 1492, while English's current status as a global lingua franca illustrates a layered mixture of relocation diffusion through settler colonialism in North America, Australia, and elsewhere, and hierarchical diffusion through the twentieth-century economic and cultural reach of the United States, spreading first through major world cities before more gradual local adoption.