It has often been suggested that the principal gnostic myths had their origin in genuine folklore, and the difficulty of discovering traces of this lore outside of gnostic sources has been explained by supposing that the myths were Oriental and were derived either from the oral traditions of localities in which no literature was produced or from literature which is no longer extant. Nothing favorable, however, to this view can be found from a comparison of gnostic myths with the native myths of Greece or with such Oriental mythology as is preserved unmixed with philosophic exegesis. In cases where known Greek, Jewish, or Christian sources are borrowed for the myths, the effort to extract gnostic theology is as painful as in the worst attempts of the Stoic exegetes, but where the myth is distinctively gnostic the philosophic meaning is easily traced in the story's plot. The reason for this is evidently not that Oriental myths are more philosophic than Greek but that gnostic myths are in their origin artificial and symbolic. Reminiscences of Oriental fancy may occasionally appear, but they do not control the main structure of the plots and can usually be detected by the difficulty with which a philosophic meaning is attached to them. An underlying structure of thought invariably conditions the imaginative forms of gnostic myths, so that theological differences between related sects are often apparent only in minor variations in the development of the story. These variations are difficult to interpret in systems of which we have only a fragmentary knowledge, and it is dangerous to patch up one system with pieces derived from another, however admirably they may seem to fit. Unlike the Stoics, who started from popular myths, the natural products of unsophisticated imagination, and explained these as symbols of philosophic truth, the gnostics invented their own myths to suit their philosophy. In course of time the best of these inventions served as the basis for further allegorizing, and some of the later gnostics, like the authors of Pistis Sophia, forgot, or neglected, the philosophy of their masters and elaborated only the mythological elements in their theology. Since they were men of feeble abilities, they only made bad myths into worse ones, and obscured the philosophic meaning which was really symbolized in the earlier forms of the stories, stiff and artificial though they were.