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God the Sovereign Good
and the Desire for Happiness 
When speaking of God as supreme being and supreme truth we saw that a multiplicity of beings resembling one another in one and the same perfection, such as goodness, is insufficient to account for the unity of likeness thus existing in that multiplicity; as Plato said, the multiple cannot account for the one. Moreover, none of the beings possessing the perfection in an imperfect degree is sufficient to account for it; for each is a compound of the perfection and the restricted capacity limiting it, and like all compounds it demands a cause: "Things in themselves different cannot possess an element in common except through a cause uniting them."  This compound participates or has a part in the perfection; it has therefore received the perfection, and can have received it only from Him who is perfection itself, which in its notion implies no imperfection.
From the moral point of view this doctrine becomes of vital importance in reminding us that the more we realize our limitations in wisdom and goodness, the more our minds should dwell on Him who is wisdom and goodness itself. The multiple finds its explanation only in the one, the diverse in the identical, the compound in the simple, the imperfect mingled with imperfection only in the perfect that is free from all imperfection.
This proof for the existence of God contains implicitly another which St. Thomas develops elsewhere, Ia IIae, q. 2, a. 8. He shows that beatitude or true happiness, the desire for which is natural to man, cannot be found in any limited or restricted good, but only in God Who is known at least with a natural knowledge and loved with an efficacious love above all things. He proves that man's beatitude cannot consist in wealth, honors, or glory, or in any bodily good; nor does it consist in some good of the soul, such as virtue, nor in any limited good. His argument for this last is based on the very nature of our intellect and will. 
Let us consider (1) the fact which is the starting-point of the proof, (2) the principle on which the proof rests, (3) the culminating point of the proof, and (4) what the proof cannot extend to.
1) The fact of experience: true, substantial, and enduring happiness cannot be found in any passing good
We can ascend to the sovereign good, the source of perfect and unalloyed happiness, by starting either from the notion of imperfect subordinate goods or from the natural desire which such goods never succeed in satisfying.
If we begin with those finite limited goods which man is naturally inclined to desire, we very soon realize their imperfection. Whether it be health or the pleasures of the body, riches or honors, glory or power, or a knowledge of the sciences, we are forced to acknowledge that these are but transitory goods, extremely limited and imperfect. But, as we have said repeatedly, the imperfect, or the good mingled with imperfection, is no more than a good participated in by the restricted capacity of the recipient, and it presupposes the pure good completely excluding its contrary. Thus a wisdom associated with ignorance and error is no more than a participated wisdom, presupposing wisdom itself. This is the metaphysical aspect of the argument, the dialectic of the intellect proceeding by way of both exemplary and efficient causality.
But the proof we are here speaking of becomes more vital, more convincing, more telling, if we begin with that natural desire for happiness which everyone feels so keenly within him. This is the psychological and moral aspect of the argument, the dialectic of love founded on that of the intellect and proceeding by way of efficient (productive, regulative) causality or final causality.  These, the efficient and final, are the two extrinsic causes, each as necessary as the other. Indeed the final is the first of the causes, so that Aristotle (Metaphysics, Bk. XII, chap. 7) saw more clearly the final causality of God the pure act than His efficient causality, whether productive or regulative. 
Following in the wake of Aristotle and St. Augustine, St. Thomas (Ia IIae, q .2, a.7, 8) insists on the fact that man by his very nature desires to be happy. Now man's intellect, transcending as it does the sense and the imagination of the brute, has knowledge not merely of this or that particular good, whether delectable or useful --- a particular food or a particular medicine, for instance --- but of good in general (universal in predication), constituting it as such, as the desirable wherever it is to be found. Since this is so, and since man's inclination is directed to the real good to be found in things, and not simply to the abstract idea of the good, it follows that he cannot find his true happiness in any finite limited good, but in the sovereign good alone (universal in being and causation). 
It is impossible for man to find in any limited good that true happiness which by his very nature he desires, for his intellect, becoming immediately aware of the limitation, conceives forthwith the idea of a higher good, and the will
naturally desires it.
This fact is expressed in the profound sentence of St. Augustine's Confessions (Bk. I, chap. I): "Our heart, a Lord, is restless, until it finds its rest in Thee" (irrequietum est cor nostrum donec requiescat in Te, Domine).
Who of us has not experienced this fact in his intimate life? In sickness we have the natural desire to recover our health as a great good. But, however happy we are in our recovery, no sooner are we cured than we realize that health alone cannot bring happiness: a man may be in perfect health and yet be overwhelmed with sadness. It is the same with the pleasures of the senses: far from being sufficient to give us happiness, let them be abused ever so little and they bring only disillusion and disgust; for our intellect, with its conception of a universal unlimited good, straightway tells us: "Now that you have obtained this sensible enjoyment which just now had such an attraction for you, you see that it is sheer emptiness incapable of filling the deep void in your heart, of satisfying your desire for happiness."
It is the same with wealth and honors, which many desire eagerly. We no sooner possess them than we realize how ephemeral and superficial is the satisfaction they give, how inadequate they, too, are to fill the void in our hearts. And intellect tells us that all these riches and honors are still but a poor finite good that is dissipated by a breath of wind.
The same must be said of power and glory. One who is lifted up on the wheel of fortune has scarcely reached the top when he begins to descend; he must give place to others, and soon he will be as a star whose light is extinguished. Even if the more fortunate retain their power and glory for a time, they never find real happiness in it; often they experience such anxiety and weariness of mind that they long to withdraw from it all.
The same applies to the knowledge of the sciences. Here it is a case of only an extremely limited good; for the true, even when complete and without admixture of error, is still the good of the intellect, not of man as a whole. Besides the intellect, the heart and will have also their profound spiritual needs, and so long as these remain unsatisfied there can be no true happiness.
Shall we find it in a most pure and exalted form of friendship? Such a friendship will doubtless bring us intense joy, sometimes affecting our inmost being. But we have an intellect that conceives universal and unlimited good, and here again it will not be long in perceiving that this most pure and exalted form of friendship is still but a finite good. This reminds us of those words of St. Catherine of Siena: "Would you continue long to slake your thirst with the cup of true friendship? Leave it, then, beneath the fountain of living water; otherwise it will speedily be drained and no longer satisfy your thirst." If the thirst is satisfied, it is because the person loved is made better, and in order to be made better he needs to receive a new goodness from a higher source.
Suppose we could look upon an angel and see his suprasensible, purely spiritual beauty. Once the first sense of wondering amazement had passed, our intellect, with its conception of the universal, unlimited good, would immediately remind us that even this was no more than a finite good and thereby exceedingly poor in comparison with the unlimited and perfect good itself. Two finite goods, however unequal they may be, are equally remote from the infinite; in this respect the angel is as insignificant as the grain of sand.
2) The principle by which we ascend to God
Can it be that this natural desire for happiness, which we all have within us, must forever remain unsatisfied? Is it possible for a natural desire to be of no effect, chimerical, without meaning or purpose?
That a desire born of a fantasy of the imagination or of an error of reason, such as the desire to have wings, may be chimerical, can well be understood. But surely it could not be so with a desire which has its immediate foundation in nature without the intervention of any conditional judgment. The desire for happiness is not a mere hypothetical wish; it is innate, with its immediate foundation in nature itself; and nature again is stable and constant, being found in all men, in all places, and at all times. Furthermore, this desire is of the very nature of the will, which, prior to any act, is an appetitive faculty having universal good as its object. The nature of our will can no more be the result of chance, of a fortuitous encounter, than can the nature of our intellect; because, like the intellect, the will is a principle of operation wholly simple, in no way compounded of different elements that chance might have brought together. Can this natural desire of the will be chimerical?
In answer to this question we say, first, that natural desire in beings inferior to ourselves is not ineffectual, as the naturalists have shown from the experimental point of view. In herbiverous animals the natural desire is for herbaceous food, and this they find; in carnivores the desire is to find flesh to eat, and they find it. Man's natural desire is for happiness, and with him true happiness is not and cannot be found in any limited good. Is this true happiness nowhere to be found? Is man's natural desire, then, to remain a deception and without finality when the natural desire of inferior beings is not in vain?
And this is not purely a naturalist's argument based on experience and the analogy of our own natural desire with that of inferior beings. It is a metaphysical argument based on the certitude of the absolute validity of the principle of finality.
If the natural desire for true happiness is chimerical, then all human activity, inspired as it is by that desire, is without finality, without a raison d'être, and thus contrary to the necessary and evident principle that every agent acts for an end. To grasp the truth of this principle, thus formulated by Aristotle, it is enough to understand the terms of the proposition. Any agent whatsoever, conscious or unconscious, has an inclination to something determinate which is appropriate to it. Now the end is precisely that determinate good to which the act of the agent or the motion of the mobile object is directed.
This principle, self-evident to one who understands the meaning of the words agent and end, may be further demonstrated by a reductio ad absurdum; for otherwise, says St. Thomas (Ia IIae, q. 1, a. 2), "there would be no reason why the agent should act rather than not act, no reason why it should act in this way rather than in another," why it should desire this object rather than some other.
If there were no finality in nature, if no natural agent acted for some end, there would be no reason why the eye should see and not hear or taste, no reason why the wings of the bird should be for flying and not for walking or swimming, no reason for the intellect to know rather than desire. Everything would then be for no purpose, and be unintelligible. There would be no reason why the stone should fall instead of rising, no reason why bodies should attract rather than repel one another and be dispersed, thus destroying the harmony of the universe.
The principle of finality has an absolute necessity and value. It is no less certain than the principle of efficient causality, that everything that happens and every contingent being demands an efficient cause, and that in the last analysis everything that happens demands an efficient cause itself uncaused, a cause that is its own activity, its own action, and is therefore its existence, since action follows being and the mode of action the mode of being.
These two principles of efficient and final causality are equally certain, the certitude being metaphysical and not merely physical, antecedent to a demonstration of the existence of God. Indeed, without finality, efficient causality is inconceivable: as we have just seen, it would be without a purpose and consequently unintelligible.
3) The term of this ascent
There is, then, a purpose in our natural desire for happiness; its inclination is for some good. But is this inclination for a good that is wholly unreal, or, though real, yet unattainable?
In the first place, the good to which our natural desire tends is not simply an idea in the mind, for, as Aristotle more than once pointed out, whereas truth is formally in the mind enunciating a judgment, the good is formally in things. When we desire food, it is not enough for us to have the idea: it is not the idea of bread that nourishes, but the bread itself. Hence the natural desire of the will, founded as it is in the very nature of the intellect and the will and not merely in the imagination or the vagaries of reason, tends to a real good, not merely to the idea of the good; otherwise it is no longer a desire and certainly not a natural one.
It will perhaps be said that our universal idea of good leads us to seek happiness in the simultaneous or successive enjoyment of all those finite goods that have an attraction for us, such as health and bodily pleasures, riches and honors, the delight in scientific knowledge, art and friendship. Those who in their mad career wish to enjoy every finite good, one after another, if not all at once, seem for the moment to think that herein lies true happiness.
But experience and reason undeceive us. That empty void in the heart always remains, making itself felt in weariness of spirit; and intelligence tells us that not even the simultaneous possession of all these goods, finite and imperfect as they are, can constitute the good itself which is conceived and desired by us, any more than an innumerable multitude of idiots can equal a man of genius.
Quantity has nothing to say in the matter; it is quality of good that counts here. Even if the whole sum of created goods were multiplied to infinity they would not constitute that pure and perfect good which the intellect conceives and the will desires. Here is the profound reason for that weariness of spirit which the worldly experience and which they take with them wherever they go. They pursue one thing after another, yet never find any real satisfaction or true happiness.
Now if our intellect is able to conceive a universal, unlimited good, the will also, awakened as it is by the intellect, has a range and depth that is limitless. Is it possible, therefore, for its natural desire --- which calls for a real good and not merely the idea of good --- to be chimerical and of no effect?
This natural desire, which has its foundation not in the imagination but in our very nature, is, like that nature, something fixed and unchangeable. It can no more be ineffectual than the desire of the herbivora or that of the carnivora; it can no more be ineffective than is the natural ordering --- of the eye for seeing, the ear for hearing, the intellect for knowing. If therefore this natural desire for happiness cannot be ineffective, if it cannot find its satisfaction in any finite goods or in the sum total of them, we are necessarily compelled to affirm the existence of a pure and perfect good. That is, the good itself or the sovereign good, which alone is capable of responding to our aspirations. Otherwise the universal range of our will would be a psychological absurdity, something radically unintelligible and without a purpose.
4) What does not come within the exigencies of our nature
Does it follow that this natural desire for happiness in us demands that we attain to the intuitive vision of God, the sovereign good?
By no means; for the intuitive vision of the Divine essence is essentially supernatural and therefore gratuitous, in no way due to our nature or to the nature of Angels.
This is the meaning of St. Paul's words: "Eye hath not seen, nor ear heard; neither hath it entered into the heart of man, what things God hath prepared for them that love Him. But to us God hath revealed them by His Spirit. For the Spirit searcheth all things, yea, the deep things of God" (1 Cor. 2:9).
But far inferior to the intuitive vision of the Divine essence and to Christian faith, is a natural knowledge of God as the author of nature, which is the knowledge given us by the proofs of His existence.
If original sin had not enfeebled our moral strength, this natural knowledge would have enabled us to attain to a naturally efficacious love for God as the author of nature, who is the sovereign good known in a natural way.
Now had man been created in a purely natural state, he would have found in this natural knowledge and naturally efficacious love for God his true happiness. Of course it would not have been that absolutely perfect and supernatural beatitude, which is the immediate vision of God, but a true happiness, nevertheless, one solid and lasting; for in the natural order, at any rate, the order embracing everything our nature demands, this natural love for God, if efficacious, does really direct our life to Him and in a true sense enables us to find our rest in Him. Such in the state of pure nature would have been the destiny of the immortal souls of the just after the probation of this life. The soul naturally desires to live forever, and a natural desire of this kind cannot be ineffective. (Cf. St. Thomas, Ia, q. 75, a. 6, c, end.)
But gratuitously we have received far more than this: we have received grace which is the seed of glory, and with it supernatural faith and a supernatural love for God, who is no longer the author merely of nature but also of grace.
And so, for us Christians, the proof we have been discussing receives strong confirmation in the happiness and peace to be found even here on earth through union with God.
In a realm far beyond any glimpse that philosophical reason might obtain, though not yet the attainment of the perfect beatitude of heaven, true happiness is ours to the extent that we love the sovereign good with a sincere, efficacious, generous love, and above all things, more than ourselves or any creature, and to the extent that we direct our whole life daily more and more to Him.
In spite of the occasional overwhelming sorrows of this present life, we shall have found true happiness and peace, at least in the summit of the soul, if we love God above all things; for peace is the tranquillity that comes with order, and here we are united to the very principle of all order and of all life.
Our proof thus receives strong confirmation from the profound experiences of the spiritual life, in which are realized the words of our Lord: "Peace I leave with you: My peace I give unto you: not as the world giveth, do I give unto you" (John 14:27). It is not in the accumulation of pleasures, riches, honors, glory, and power, but in union with God, that the Savior has given us peace. So solid and enduring is the peace He has given us that He can and actually does preserve it within us, as He predicted that He would, even in the midst of persecutions: "Blessed are the poor. ... Blessed are they that hunger and thirst after justice. ... Blessed are they that suffer persecution for justice' sake, for theirs is the kingdom of Heaven" (Matt. 5:10). Already the kingdom of heaven is theirs in the sense that in union with God they possess through charity the beginnings of eternal life, inchoatio vitae aeternae (IIa IIae, q. 24, a. 3 ad 2um).
Epicurus boasted that his teaching would bring happiness to his disciples even in the red-hot brazen bull of Phalaris in which men were roasted to death. Jesus alone has been able to accomplish such a thing by giving to the Martyrs in the very midst of their torments peace and true happiness through union with God.
According to the degree of this union with God, the proof we have been discussing is thereby very much confirmed by reason of the profound spiritual experience; for, through the gift of wisdom, God makes Himself felt within us as the life of our life: "For the Spirit Himself giveth testimony to our spirit that we are the sons of God" (Rom. 8:16). God makes Himself felt within us as the principle of that filial love for Him which He Himself inspires in us.
1. We here reproduce the substance of a study we have developed at greater length in another work entitled: Le réalisme du principe de finalité, Part II; chap. 5, "La finalité de la volonte: le désir naturel du bonheur prouve-t-il l'existence de Dieu?"
2. St. Thomas, Ia. q. 3. a. 7. and De Potentia, q. 3. a. 5.
3. Cf. Summa Theologica, Ia IIae, q. 2, a. 8.
4. Cf. Ibid., Ia IIae, q. 1, a. 4: "Is there an ultimate end to human life?" "Absolutely speaking, it is impossible in a series to continue to infinity in any direction. ... Were there not an ultimate end, nothing would be desired, no action would have a term, nor would the inclination of the agent find repose."
5. If, instead of considering simply the end of this natural desire, we consider its ordering to that end --- and this demands an efficient, regulating cause (ordinans vel imperans movet ut agens, non ut finis) --- then the argument pertains to the fifth way of St. Thomas, which is that based upon the presence of order in the world: "All design presupposes a designer." In this sense the passive ordering of our will to the bonum honestum or moral good, superior alike to the delectable and to the useful, presupposes a supreme regulator, Or again, moral obligation, which is displayed in remorse of conscience and in the peace that comes from duty accomplished, presupposes a supreme lawgiver. Of this we will speak in the next
6. Cf. Cajetan, Commentary on Ia IIae, q. 2, a. 7.