Summa contra Gentiles3.39 Chapter XXXIX. That man’s happiness does not consist in the know- ledge of God acquired by demonstration

There is also another knowledge of God, higher than the one just mentioned, which is acquired by means of a demonstration, and which approaches nearer to a proper knowledge of him: since by means of a,;demonstration many things are removed from him, so that in consequence we understand him as something apart from other things.’ For demonstration proves that God is immovable, eternal, incorporeal, utterly simple, one, and the like, as we have shown in the First Book. Now we arrive at the proper knowledge of a thing not only by affirmation, but also by negation: for just as it is proper to man to be a rational animal, so is it proper to him not to be inanimate or irrational. Yet there is this difference between these two modes of knowledge, that when we have proper knowledge of a thing by affirmation, we know what that thing is, and how it is distinguished from others: whereas when we have proper knowledge of a thing by negations, we know that it is distinct from others, but remain ignorant of what it is. Such is the proper knowledge of God, that can be obtained by demonstrations. But neither does this suffice for man’s ultimate happiness. For things belonging to one species for the most part attain to the end of that species, because nature achieves its purpose always or nearly always, and 1 Bk. I., ch, xiv. III 6 fails in a few instances on account of some corruption. Now happiness is the end of the human species; since all men naturally desire it. Therefore happiness is a common good that can be attained by all men, unless some obstacle occur to some whereby they be debarred from it. Few, however, attain to the possession of the aforesaid knowledge of God by way of demonstration, on account of the obstacles to this knowledge, mentioned at the beginning of this work.’ Therefore this knowledge is not essentially man’s happiness.

Again. Actual existence is the end of that which exists potentially, aswas made clear above.? Wherefore happiness that is the last end, is an act free of any potentiality to a further act. Now this knowledge of God that is acquired by way of demonstration is still in potentiality to a further knowledge of God, or to the same knowledge, but by a better way: because those who came afterwards endeavoured to add something to the knowledge of God besides that which they found handed down to them by those who preceded them. Therefore such knowledge is not man’s ultimate happiness.

Further. Happiness excludes all unhappiness: for no man can be at the same time happy and unhappy. Now > deception and error have a large place in unhappiness, since all naturally avoid them. But the aforesaid knowledge of God is subject to the admixture of many errors: as evidenced by many who knew some truths about God through demonstration, yet, following their own opinions, when they lacked proof, fell into many errors. And if some there were who by the way of demonstration discovered the truth about divine things, without any admixture of error in their opinions, it is evident that they were very few: which is inconsistent with happiness which should be the common end. Therefore man’s ultimate happiness is not seated in such knowledge as this.

Moreover. Happiness consists in a perfect operation. Now perfect knowledge requires certitude: hence we cannot be said to know, unless we be certain that it cannot be otherwise, as stated in 1 Postey. ii. But the aforesaid knowledge is beset with uncertainty: as evidenced by the diversity of sciences about divine things, elaborated by those who endeavoured to discover something about them by the way of demonstration. Therefore ultimate happiness does not consist in suchlike knowledge.

Besides. When the will has obtained its last end, its desire is at rest. Now the ultimate end of all human knowledge is happiness. Therefore happiness is essentially that knowledge of God the possession of which leaves no knowledge to be desired of anything knowable. Such, however, is not the knowledge which philosophers were able to have about God by the way of demonstration: because even when we have that knowledge we still desire to know something more;—things that we know not by means of the aforesaid knowledge. Therefore happiness does not consist in suchlike knowledge of God.

Furthermore. The end of/everything that is in potentiality is that it be brought to actuality: for to this does it tend by means of the movement with which it is moved to its end. Now everything that is in potentiality tends to be actualized as far as possible. For there are things in potentiality in that their whole potentiality is reducible to act:

be actualized: thus a heavy body, that is outside its medium, is in potentiality to its proper place. There are also things whose potentiality cannot be actualized all at once,—for instance primary matter: so that by its movement it is appetent of actualization by various forms in succession, which cannot be in matter at the same time on account of their diversity. Now our intellect is in potentiality to all things intelligible, as stated in the Second Book.t And it is possible for two intelligible objects to be in the possible intellect at the same time in respect of the first act which is science: although perhaps not in respect of the second act which is consideration. Accordingly it is clear that the whole potentiality of the possible intellect can be actualized at one time: and consequently this is required for its ultimate end which is happiness. But the aforesaid knowledge which can be acquired about God by the way of demonstration, does not effect this: since when we have it we still are ignorant of many things. Therefore suchlike knowledge of God does not suffice for ultimate happiness.