the subject-matter of dogmatic theology. The existence of the former of these, it is true, as of the latter, may be obscured and nearly obliterated by sin and the consequent disorganization; for in the teaching of the Fathers, as in that of their Master, it is the pure in heart that see God,[48] and it is only the man whose nature is kept in due balance by a life of moral rectitude—the "righteous man" of the Scriptures—who can be expected to exhibit clearly this "natural opinion" or to attain to a full knowledge and appreciation of the Christian doctrine of God. At the very best, the knowledge of the Deity attained apart from revelation seemed to the Fathers to be, in comparison with their own certainty, miserably vague and conjectural, and they are constantly contrasting, in the most striking and graphic way, the contradictory and uncertain results to which the philosophers attained with the definiteness and consistency of the already well-defined doctrine of the Christian church. To them certainty in regard to knowledge of God can only come by means of the testimony of one who had seen and known,[49] and this testimony they are satisfied that they find in two places chiefly—first, in the testimony of the Prophets of the Old Testament, and, second, but in fact primarily, in the life and words of Jesus Christ, "the Word."

Of the antiquity and reliability of this first source—the Prophets—they were never tired of talking, and they were so confident of the necessity of resorting to it that they developed their famous theory of the indebtedness of Plato and Aristotle to those Hebrew seers for their theology. "From every point of view, therefore," concludes St. Justin Martyr, "it must be seen that in no other way than only from the prophets, who teach us by divine inspiration, is it at all possible to learn anything concerning God and the true religion."[50]

But the chief source from which the Fathers drew that certainty which they could not find in the demonstrations of philosophy was in the teaching of the Word, Jesus Christ. God, indeed, as we have seen, is not an object of science, "but the Son is wisdom and knowledge and truth, and all else that has affinity thereto. He is also susceptible of demonstration and of description."[51] It is in the incarnate Word of God that the patristic writers find expressed all that man is able to comprehend, and all that he needs to know in this present world, of the Divine Nature, and it is His words that confirm their confidence in that "innate opinion" of the existence of God, of the presence of which in every man they were so sure.

The subject of the "demonstration" of the existence of God is spoken of at some length in several places by St. Clement of Alexandria, and with his position most of the Fathers agree in the main. He regards the subject largely from an Aristotelian point of view. All knowledge is derived from Sensation and Understanding. "Intellectual apprehension is first in the order of nature; but in our case, and in relation to ourselves, Sensation is first, and of Sensation and Understanding the essence of knowledge is formed, and evidence is common to Understanding and Sensation."[52] But "should any one say that knowledge is founded on demonstration" (which "depends on primary and better known principles,"[53] being "discourse agreeable to reason, producing belief in points disputed, from points admitted"[54]) "by a process of reasoning, let him hear that first principles are incapable of demonstration, for they are neither by art" (τέχνη), which is "practical solely, and not theoretical," "nor by sagacity" (φρόνησις = practical wisdom), which is "conversant about objects which are susceptible of change,"[55] but are "primary," "self-evident," and "indemonstrable."[56] Thus this "demonstration by a process of reasoning," apart from Sensation and Understanding, is only "to syllogize;" "for to draw the proper conclusion from the premisses is merely to syllogize. But to have also each of the premisses true is not merely to have syllogized, but also to have demonstrated," "so that if there is demonstration at all, there is an absolute necessity that there be something that is self-evident, which is called primary and indemonstrable."[57] On the basis of this theory of knowledge, it is evident that the usual arguments for the existence of God would have but little weight. For they either attempt to attain their end by formal thought alone, and thus result in mere "syllogizing;" or, starting from valid enough premises, they try to extend the conclusion beyond the limits imposed by the laws of "demonstration." For St. Clement, then, God is not "apprehended by the science of demonstration." If the Deity is to be known, there must be some place in which a union of the material and formal elements of "demonstration" of His existence is to be found. This he places in the life and teaching of Jesus Christ, who, as God incarnate, furnishes the "evidence" which "is common to Understanding and Sensation," and thus translates the "Infinite" and "Ineffable" into terms of the finite and comprehensible. In this paradox Christian theology has ever since been content to rest as one of the fundamental mysteries of the Faith.

But even with all the aids of revelation, the Fathers would not claim that man can advance to a full or adequate knowledge of God—we can simply know so much about God as is necessary for practical purposes—for ascertaining our proper end and duties. God is, from the very limitations of the human mind, "ineffable," "incomprehensible," "the unknown;"[58] and St. Clement of Alexandria expressly states even the best knowledge of God that man can by any means attain is only negative.