It is not surprising, therefore, that the reasoning just outlined is usually supplemented by a further consideration. It is maintained, namely, that the mystic piety of paganism forms to some extent a unit; it was not a mere fortuitous collection of beliefs and practices, but was like an enveloping spiritual atmosphere of which, despite variations of humidity and temperature, the fundamental composition was everywhere the same. If, therefore, the presence of this atmosphere of mystical piety can be established here and there in sources of actually pre-Christian date, the investigator has a right to determine the nature of the atmosphere in detail by drawing upon later sources. In other words, the mystical religion of the Hellenistic age is reconstructed in detail by the use of post-Christian sources, and then (the essential unity of the phenomenon being assumed) the early date of this oriental mystical religion is established by the scanty references in pre-Christian times. It is admitted, perhaps, that the elements of oriental mysticism actually found in pre-Christian sources would not be sufficient to prove dependence of Paul upon that type of religion; but the elements found in later sources are thought to be so closely allied to those which happen to have early attestation that they too must be supposed to have been present in the early period, and since they are similar to Paulinism they must have exerted a formative influence upon Paul's religion. To put the matter briefly, the nature of Hellenized oriental religion is established by post-Pauline sources; whereas the early origin of that religion is established by the scanty pre-Christian references. This procedure constitutes a curious reversal of the procedure which is applied by the very same scholars to Christianity. Christianity is supposed to have undergone kaleidoscopic changes in the course of a few years or even months, changes involving a transformation of its inmost nature; yet pagan religion is apparently thought to have remained from age to age the same. When Paul, only a few years after the origin of the Church, says that he "received" certain fundamental elements in his religion, the intimate connection of those elements with the rest of the Pauline system is not allowed to establish the early origin of the whole; yet the paganism of the third and fourth centuries is thought to have constituted such a unity that the presence of certain elements of it in the pre-Christian period is regarded as permitting the whole system to be transplanted bodily to that early time.