XX. And in the first place, they who presume to compare that Substance, which has no Superior, and is above all Cause, and free from all Laws, to that which is Begotten, and ^[19] is subservient to the Laws of its Father, seem either not at all to consider the nature of Things, or not to form their Judgments about them with an uncorrupt Mind. For there are plainly two ways cut out for the Discovery of the Truth in such Questions; the one of which is a priori, whereby we confider the Substances of things themselves, and by fair and clear Reasoning we determine about every one of them; the other of which is a posteriori, whereby we make the Enquiry from the Effects to the Cause, and so distinguish Substances by the Creatures they make, and by their Operations. Nor is it possible to perceive that either of these ways can discover this Likeness of Substance.

For in case any one takes the Rise of his Enquiries from the Substances themselves, and finds that One is superior to all Dominion, and above all Generation, and all Indigency; This will teach a Mind that comes with a sincere Desire after Truth, and oblige it to reject with the greatest Indignation, from the very Law and Rule of Nature, all Companion between them; and will give us to understand, that the Operation must be sutable and agreeable to the Dignity of the Substance. But in case he first regards the Creatures made, and thence goes back to the Substances, when he finds the Son to be the Being made by the Unbegotten Being, and the Comforter the Being made by the Only Begotten, and is satisfy'd of the difference of the Operations by the Supereminence of the Only Begotten; he will thence perceive an indisputable Demonstration of the Difference of their Substances. Not here to add a third Difference, ^[20] that be who creates by his own Power, must be vastly superiour to him that does it at the pleasure of his Father, and confesses that he does nothing of himself;⁷ and he that is ador'd, from him that adores.