The history, then, of the Gaels is that of an isolated branch of the Keltic stock; and it is this isolation which creates the difficulties of their ethnology. No historical records throw any light upon their origin--a statement which the most sanguine investigator must admit. But tradition, perhaps, is less uncommunicative. Many investigators believe this. For my own part I should only be glad to be able to do so. As it is, however, the arguments of the present chapter will proceed as if the whole legendary history of Ireland and Scotland, so far as it relates to the migrations by which the islands were originally peopled by the Gaels, were a blank--the reasons for the scepticism being withheld for the present. But only for the present. In the seventh chapter they will be given as fully as space allows. The present arguments rest wholly upon a fact of which the importance has more than once been foreshadowed already, and which the reader anticipates. Let us say, for the sake of illustration, that the British and Gaelic differ from each other as the Latin and Greek. The parallel is a rough one, but it will suffice as the basis of some criticism. Languages thus related cannot be in the relation of mother and daughter, _i.e._, the one cannot be derived from the other, as the English is from the Anglo-Saxon, or the Italian from the Latin. The true connexion is different. It is that of brother and sister, rather than of parent and child. The actual source is some common mother-tongue; a mother-tongue which may become extinct after the evolution of its progeny. Hence, in the particular case before us, the Gaelic and British must have developed themselves, each independently of the other, out of some common form of speech. And the development must have taken place within the British Islands; the doctrine being that out of a language which at some remote period was neither British nor Gaelic, but which contained the germs of both, the western form of speech took one form, the southern another--the results being in the one case the British, in the other the Gaelic, tongue.