Berkeley showed that it is simply impossible for any human being to make to himself a general image of a triangle, for such an image would have to be at the same time right-angled, obtuse-angled, acute-angled, and other kinds also; such an object does not exist; whereas it is perfectly possible to have an image of any single triangle; to name some characteristic features common to all triangles, and thus to form a name and at the same time a concept of a triangle.[45] This mental process which Berkeley described so well as applied to modern concepts we can adopt with regard to all, even the most primitive. Man, in entering a forest, discovered in the trees something that was interesting to him. For practical purposes trees were particularly interesting to the primitive framers of language, because they could be split in two, three, or four pieces, cut, shaped according to the size of the piece into blocks, planks, boats, and shafts; any object for which the necessity had made itself felt. Hence, from a root _dar_, to tear, our Aryan ancestors called trees _dru_, or _dâru_, literally what can be torn, or split, or cut; from the same root the Greeks called the skin of an animal _dérma_, because it was torn off, and a sack _dóros_ (in Sanscrit _driti_), because it was made of leather, and a spear _dóry_, because it came from a tree, and was cut and shaped and planed. Such words being once given would produce many offshoots; the Celts of Gaul and of Ireland called their priests _Druids_, literally the men of oak-groves. The Greeks called the spirits of the forest trees _Dryades_; and the Hindoos called a man of wood, or a man with a wooden, or, as we say, flinty heart, _dâruna_, cruel. The immense number of intelligible roots gave birth to many new images, these roots crossed and recrossed, for the concepts of to go, to give, to move, to make, would be the foundations of others, in some ways differing; one idea or thought in its flight would meet others perhaps of a conflicting nature, thoughts and words would equally undergo incessant modifications, which fact explains why in these earlier stages of language the members of a community soon ceased to understand each other if separated but for a short period of time. Ovid, in speaking of the chaos at the beginning of the world, makes a picture which would equally well describe the birth of language. “Matter was in an unformed mass ... the sky, the earth, the sea had all one aspect; there where was the earth, was also the sea, and the sky was there also.” The extraordinary destinies of the roots I have named constitutes a short chapter only, in the birth and development of tongues; but short as it is, it suffices to give us an idea of the elastic nature of these roots, their faculty of extension, and the part they play in the economy of language, and in the administration of the affairs of the human mind.