"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."