But in speaking of “cause,” and “of the cause,” we do not by these words denote nature (for no one would give the same definition of “cause” and of “nature”), but we indicate the difference in manner of existence. For when we say that one is “caused,” and that the other is “without cause,” we do not divide the nature by the word “cause”, but only indicate the fact that the Son does not exist without generation, nor the Father by generation: but we must needs in the first place believe that something exists, and then scrutinize the manner of existence of the object of our belief: thus the question of existence is one, and that of the mode of existence is another. To say that anything exists without generation sets forth the mode of its existence, but what exists is not indicated by this phrase. If one were to ask a husbandman about a tree, whether it were planted or had grown of itself, and he were to answer either that the tree had not been planted or that it was the result of planting, would he by that answer declare the nature of the tree? Surely not; but while saying how it exists he would leave the question of its nature obscure and unexplained. So, in the other case, when we learn that He is unbegotten, we are taught in what mode He exists, and how it is fit that we should conceive Him as existing, but what He is we do not hear in that phrase. When, therefore, we acknowledge such a distinction in the case of the Holy Trinity, as to believe that one Person is the Cause, and another is of the Cause, we can no longer be accused of confounding the definition of the Persons by the community of nature.