Elements of ornament flow into the ceramic art from a number of sources, but chiefly in two great currents: the one from art, and consisting chiefly of technical or mechanically produced phenomena, and hence geometric, and the other from nature, and carrying elements primarily delineative, and hence non-geometric. When once within the realm of decoration the various motives or elements are subject to modification by two classes of influences or conditioning forces: the technical restraints of the art and the esthetic forces of the human mind. Mechanical and geometric elements, although born within the art or its associated arts, are modified in the processes of adaptation to the changing requirements and conditions of the art and through the tendency towards elaboration under the guidance of the esthetic forces; left by themselves they remain, throughout all changes of use and modification of form, purely geometric. Imitative elements tend, under the same influences, to move in the direction of the unreal or geometric. In this way the realistic forms undergo marked changes, gradually assuming a geometric character and finally losing all semblance of nature.
Now it must be noted that the decorations of any group of art products may embody both classes of elements or they may be restricted rather closely to either. This fact enables us to account for many of the strongly marked distinctions observed in the decorative systems of different communities, races, and times. In a recent study of ancient Pueblo art I traced the decoration to a mechanical origin, mainly in the art of basketry, and thus accounted for its highly geometric character. Chiriquian art presents a strong contrast to this, as the great body of elements are manifestly derived from nature by delineative imitation. It was further observed in Pueblo art that as time went on life forms were little by little introduced into its decoration and that in recent times they shared the honors equally with the primitive geometric forms. In Chiriquian art we find but meager traces of a primitive geometric system, and conclude that either the earliest art of the people did not give rise to such a system or that the graphic motives, entering gradually and steadily multiplying, supplanted the archaic forms, finally usurping nearly the entire field. As noticed in the preceding sections, there is always a certain amount of geometricity in the arrangement and the enframing of the designs, as well as a certain degree of convention in the treatment of even the most graphic motives; but these characters may be due to the restraining conditions of the art, rather than to the survival of original or ancestral features or characters.