ABSTRACT

This chapter outlines the way in which linguistic trees are typically understood, before examining their underlying assumptions. Trees and waves constitute two competing attempts at representing the same thing, namely historical events of early language-internal ‘horizontal’ diffusion, apprehended through the traces they left in modern languages, via later ‘vertical’ transmission. The chapter examines the processes that underlie genealogical relations between languages, and explains why the Tree Model is most often unsuited for representing them. While the Comparative Method must be preserved for its invaluable scientific power, a rigorous application of its principles in situations of linkage in fact disproves the Tree Model, and favours the Wave Model as a more accurate description of the genealogy of languages. When historical linguists identify a change that happened ‘once’ in a ‘language’, they really encapsulate a long process of diffusion that took place across large networks of idiolects, sometimes spanning across several generations.