Tree Model

In historical linguistics, the Tree Model (German Stammbaumtheorie), or more recently the Genetic or Cladistic Model, is a model of language change described by an analogy with the concept of family tree. In this scientific metaphor, the family members are languages, the family is a language family and the birth kinships of people are genetic relationships between languages. A language that can therefore be a parent or mother language or a daughter language (fathers and sons are not in the metaphor). Languages can have lines of descent, can be cognate and can be "related." In this metaphor, languages are treated as objects sui generis ("of their own kind"). The biological or sociological circumstances of the speakers are completely irrelevant. They may be biologically related or unrelated, kin or not, but are ignored indifferently by the metaphor.

A language tree, or family tree with languages substituted for real family members, has the form of a node-link diagram of a logical tree structure. Such a diagram contains branch points, or nodes, from which the daughter languages descend by different links. The nodes are proto-languages or common languages. The concept of descent of a language means that a linked language was created by a process of gradual modification over time of the language at the next-earliest node. Modification is detected or hypothesized in comparative linguistics by comparing features in one language that appear similar to parallel features in another. A common ancestor is then assumed for the feature, rightly or wrongly, if a rule can be found to explain the modification.