their technical vocabulary; the majority of good writers and speakers of English is the only authority which can make a word good English in the part of our tongue that we all alike use and value; while all the learned of Europe must join together, in order to alter the notation of a number, or the symbol of a chemical element. But the principle is everywhere the same: as mutual intelligibility is the bond which makes the unity of a language, so the necessity of mutual intelligibility is the power which preserves and perpetuates that unity.
If communication is thus the assimilating force which averages and harmonizes the effects of discordant individual action on language, keeping it, notwithstanding its incessant changes, the same to all the members of the same community, then it is clear that everything which narrows communication, and tends to the isolation of communities, favours the separation of a language into dialects; while all that extends communication, and strengthens the ties which bind together the parts of a community, tends to preserve the homogeneity of speech. Suppose a race, occupying a certain tract of country, to possess a single tongue, which all understand and use alike: then, so long as the race is confined within narrow limits, however rapidly its language may yield to the irresistible forces which produce linguistic growth, all will learn from each, and each from all; and, from generation to generation, every man will understand his neighbour, whatever difficulty he might find in conversing with the spirit of his great-grandfather, or some yet remoter ancestor. But if the race grows in numbers, spreading itself over region after region, sending out colonies to distant lands, its uniformity of speech is exposed to serious danger, and can only be saved by specially favouring circumstances and conditions. And these conditions are yet more exclusively of an external character than those which, as we lately saw, determine the mode and rate of linguistic change in general: they consist mainly in the kind and degree of culture enjoyed and the effects which this naturally produces. In a low state of civilization, the maintenance of community over a wide extent of country is altogether impracticable; the tendency
