Tree model

"Though the earth were widely peopled before the flood ... yet whether, after a large dispersion, and the space of sixteen hundred years, men maintained so uniform a language in all parts, ... may very well be doubted."

"It may be worth while to illustrate this view of classification, by taking the case of languages. If we possessed a perfect pedigree of mankind, a genealogical arrangement of the races of man would afford the best classification of the various languages now spoken throughout the world; and if all extinct languages, and all intermediate and slowly changing dialects, had to be included, such an arrangement would, I think, be the only possible one. Yet it might be that some very ancient language had altered little, and had given rise to few new languages, whilst others (owing to the spreading and subsequent isolation and states of civilisation of the several races, descended from a common race) had altered much, and had given rise to many new languages and dialects. The various degrees of difference in the languages from the same stock, would have to be expressed by groups subordinate to groups; but the proper or even only possible arrangement would still be genealogical; and this would be strictly natural, as it would connect together all languages, extinct and modern, by the closest affinities, and would give the filiation and origin of each tongue."

"Any language consists of thousands of forms with both sound and meaning ... any sound whatever can express any meaning whatever. Therefore, if two languages agree in a considerable number of such items ... we necessarily draw a conclusion of common historical origin. Such genetic classifications are not arbitrary ... the analogy here to biological classification is extremely close ... just as in biology we classify species in the same genus or high unit because the resemblances are such as to suggest a hypothesis of common descent, so with genetic hypotheses in language."

The comparative method has been used by historical linguists to piece together tree models utilizing discrete lexical, morphological, and phonological data. Chronology can be found but there is no absolute date estimates utilizing this system.

A phylogenetic network, one of many posited by the CPHL. The phylogenetic tree appear in black lines. The contact edges are the red lines. Here there are three, the most parsimonious number required to generate a feasible network for Indo-European.