CHAPTER XII—Of the Opinion of those who say that the Existence of God is a Tenet of Faith alone and cannot be demonstrated

THE falseness of this opinion is shown to us as well by the art of demonstration, which teaches us to argue causes from effects, as also by the order of the sciences, for if there be no knowable substance above sensible substances, there will be no science above physical science; as also by the efforts of philosophers, directed to the proof of the existence of God; as also by apostolic truth asserting: The invisible things of God are clearly seen, being understood by the things that are made (Rom. i, 20).²³²³As also by the Vatican Council defining: “If any one says that the one and true God, our Creator and Lord, cannot be known with certitude by the natural light of reason through the things that are made, let him be anathema” (Sess. 3, can. 1, De Revel.)

The axiom that in God essence and existence are the same is to be understood of the existence whereby God subsists in Himself, the manner of which is unknown to us, as also is His essence; not of the existence which signifies an affirmative judgement of the understanding. For in the form of such affirmative judgement the fact that there is a God falls under demonstration; as our mind is led by demonstrative reasons to form such a proposition declaratory of the existence of God.²⁴²⁴Compositionem intellectus. In the language of the schoolmen, componere et dividere, ‘to put together or put asunder notions,’ means to make judgements, affirmative and negative. In the reasonings whereby the existence of God is demonstrated it is not necessary to assume for a premise the essence or quiddity²⁵²⁵Quiddity, quidditas, the answer to the question quid est? — ‘What is the thing essentially?’ of God: but instead of the quiddity the effect is taken for a premise, as is done in demonstrations a posteriori from effect to cause. All the names of God are imposed either on the principle of denying of God Himself certain effects of His power, or from some habitude of God towards those effects.²⁶²⁶Uncreated, as a name of God, would be an example of the first; Father, of the second. Although God transcends sense and the objects of sense, nevertheless sensible effects are the basis of our demonstration of the existence of God. Thus the origin of our own knowledge is in sense, even of things that transcend sense.