1 Objection 1: It seems that the existence of God cannot be demonstrated. For it is an article of faith that God exists. But what is of faith cannot be demonstrated, because a demonstration produces scientific knowledge; whereas faith is of the unseen Heb. 11, 1). Therefore it cannot be demonstrated that God exists.
1 Ad secundum sic proceditur. Videtur quod Deum esse non sit demonstrabile. Deum enim esse est articulus fidei. Sed ea quae sunt fidei, non sunt demonstrabilia, quia demonstratio facit scire, fides autem de non apparentibus est, ut patet per apostolum, ad Hebr. XI. Ergo Deum esse non est demonstrabile.
2 Objection 2: Further, the essence is the middle term of demonstration. But we cannot know in what God's essence consists, but solely in what it does not consist; as Damascene says De Fide Orth. i, 4). Therefore we cannot demonstrate that God exists.
2 Praeterea, medium demonstrationis est quod quid est. Sed de Deo non possumus scire quid est, sed solum quid non est, ut dicit Damascenus. Ergo non possumus demonstrare Deum esse.
3 Objection 3: Further, if the existence of God were demonstrated, this could only be from His effects. But His effects are not proportionate to Him, since He is infinite and His effects are finite; and between the finite and infinite there is no proportion. Therefore, since a cause cannot be demonstrated by an effect not proportionate to it, it seems that the existence of God cannot be demonstrated.
3 Praeterea, si demonstraretur Deum esse, hoc non esset nisi ex effectibus eius. Sed effectus eius non sunt proportionati ei, cum ipse sit infinitus, et effectus finiti; finiti autem ad infinitum non est proportio. Cum ergo causa non possit demonstrari per effectum sibi non proportionatum, videtur quod Deum esse non possit demonstrari.
4 On the contrary, The Apostle says: The invisible things of Him are clearly seen, being understood by the things that are made Rm. 1, 20). But this would not be unless the existence of God could be demonstrated through the things that are made; for the first thing we must know of anything is whether it exists.
4 Sed contra est quod apostolus dicit, ad Rom. I, invisibilia Dei per ea quae facta sunt, intellecta, conspiciuntur. Sed hoc non esset, nisi per ea quae facta sunt, posset demonstrari Deum esse, primum enim quod oportet intelligi de aliquo, est an sit.
5 I answer that, Demonstration can be made in two ways: One is through the cause, and is called a priori, and this is to argue from what is prior absolutely. The other is through the effect, and is called a demonstration a posteriori; this is to argue from what is prior relatively only to us. When an effect is better known to us than its cause, from the effect we proceed to the knowledge of the cause. And from every effect the existence of its proper cause can be demonstrated, so long as its effects are better known to us; because since every effect depends upon its cause, if the effect exists, the cause must pre-exist. Hence the existence of God, in so far as it is not self-evident to us, can be demonstrated from those of His effects which are known to us.
5 Respondeo dicendum quod duplex est demonstratio. Una quae est per causam, et dicitur propter quid, et haec est per priora simpliciter. Alia est per effectum, et dicitur demonstratio quia, et haec est per ea quae sunt priora quoad nos, cum enim effectus aliquis nobis est manifestior quam sua causa, per effectum procedimus ad cognitionem causae. Ex quolibet autem effectu potest demonstrari propriam causam eius esse si tamen eius effectus sint magis noti quoad nos), quia, cum effectus dependeant a causa, posito effectu necesse est causam praeexistere. Unde Deum esse, secundum quod non est per se notum quoad nos, demonstrabile est per effectus nobis notos.
6 Reply to Objection 1: The existence of God and other like truths about God, which can be known by natural reason, are not articles of faith, but are preambles to the articles; for faith presupposes natural knowledge, even as grace presupposes nature, and perfection supposes something that can be perfected. Nevertheless, there is nothing to prevent a man, who cannot grasp a proof, accepting, as a matter of faith, something which in itself is capable of being scientifically known and demonstrated.
6 Ad primum ergo dicendum quod Deum esse, et alia huiusmodi quae per rationem naturalem nota possunt esse de Deo, ut dicitur Rom. I non sunt articuli fidei, sed praeambula ad articulos, sic enim fides praesupponit cognitionem naturalem, sicut gratia naturam, et ut perfectio perfectibile. Nihil tamen prohibet illud quod secundum se demonstrabile est et scibile, ab aliquo accipi ut credibile, qui demonstrationem non capit.
7 Reply to Objection 2: When the existence of a cause is demonstrated from an effect, this effect takes the place of the definition of the cause in proof of the cause's existence. This is especially the case in regard to God, because, in order to prove the existence of anything, it is necessary to accept as a middle term the meaning of the word, and not its essence, for the question of its essence follows on the question of its existence. Now the names given to God are derived from His effects; consequently, in demonstrating the existence of God from His effects, we may take for the middle term the meaning of the word God.
7 Ad secundum dicendum quod cum demonstratur causa per effectum, necesse est uti effectu loco definitionis causae, ad probandum causam esse, et hoc maxime contingit in Deo. Quia ad probandum aliquid esse, necesse est accipere pro medio quid significet nomen non autem quod quid est, quia quaestio quid est, sequitur ad quaestionem an est. Nomina autem Dei imponuntur ab effectibus, ut postea ostendetur, unde, demonstrando Deum esse per effectum, accipere possumus pro medio quid significet hoc nomen Deus.
8 Reply to Objection 3: From effects not proportionate to the cause no perfect knowledge of that cause can be obtained. Yet from every effect the existence of the cause can be clearly demonstrated, and so we can demonstrate the existence of God from His effects; though from them we cannot perfectly know God as He is in His essence.
8 Ad tertium dicendum quod per effectus non proportionatos causae, non potest perfecta cognitio de causa haberi, sed tamen ex quocumque effectu potest manifeste nobis demonstrari causam esse, ut dictum est. Et sic ex effectibus Dei potest demonstrari Deum esse, licet per eos non perfecte possimus eum cognoscere secundum suam essentiam.