The 5 ways of Saint Thomas
The existence of God can be proved in five ways. The first and more manifest way is the argument from motion. (…) The second way is from the nature of efficient cause. In the world of sensible things we find there is an order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible. Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate cause, and the intermediate is the cause of the ultimate cause, whether the intermediate cause be several, or one only. Now to take away the cause is to take away the effect. Therefore, if there be no first cause among efficient causes, there will be no ultimate, nor any intermediate, cause. But if in efficient causes it is possible to go on to infinity, there will be no first efficient cause, neither will there be an ultimate effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.
The third way is taken from possibility and necessity. (…) The fourth way is taken from the gradation to be found in things. (…) The fifth way is taken from the governance of the world.
Saint Thomas Aquinas (1225-1274), Summa Theologica.
The ontological argument
The mind … looks around in all directions in order to extend its knowledge further. First of all, it finds within itself ideas of many things; and so long as it merely contemplates these ideas and does not affirm or deny the existence outside itself of anything resembling them, it cannot be mistaken. Next, it finds certain common notions from which it constructs various proofs; and, for as long as it attends to them, it is completely convinced of their truth. For example, the mind has within itself ideas of numbers and shapes, and it also has such common notions as: If you add equals to equals the results will be equal; from these it is easy to demonstrate that the three angles of a triangle equal two right angles, and so on. And so the mind will be convinced of the truth of this and similar conclusions, so long as it attends to the premises from which it deduced them. (…)
- The existence of God is validly inferred from the fact that necessary existence is included in our concept of God.
The mind next considers the various ideas which it has within itself, and finds that there is one idea- the idea of a supremely intelligent, supremely powerful and supremely perfect being – which stands out from all the others. (And it readily judges from what it perceives in this idea, that God, who is the supremely perfect being, is, or exists. For although it has distinct ideas of many other things it does not observe anything in them to guarantee the existence of their object.) In this one idea the mind recognizes existence – not merely the possible and contingent existence which belongs to the ideas of all the other things which it distinctly perceives, but utterly necessary and eternal existence. Now on the basis of its perception that, for example, it is necessarily contained in the idea of a triangle that its three angles should equal two right angles, the mind is quite convinced that a triangle does have three angles equaling two right angles. In the same way, simply on the basis of its perception that necessary and eternal existence is contained in the idea of a supremely perfect being, the mind must clearly conclude that the supreme being does exist.
- Our concepts of other things do not similarly contain necessary existence, but merely contingent existence.
The mind will be even more inclined to accept this if it considers that it cannot find within itself an idea of any other thing such that necessary existence is seen to be contained in the idea in this way. And from this it understands that the idea of a supremely perfect being is not an idea which was invented by the mind, or which represents some chimera, but that it represents a true and immutable nature which cannot but exist, since necessary existence is contained within it.
(…) Since, then, we have within us the idea of God, or a supreme being, we may rightly inquire into the cause of our possession of this idea. Now we find in the idea such immeasurable greatness that we are quite certain that it could have been placed in us only by something which truly possesses the sum of all perfections, that, by a God who really exists. For it is very evident by the natural light not only that nothing comes from nothing but also that what is more perfect cannot be produced by – that is, cannot have as its efficient and total cause – what is less perfect.
Furthermore, we cannot have within us the idea or image of anything without there being somewhere, either within us or outside us, an original which contains in reality all the perfections belonging to the idea. And since the supreme perfections of which we have an idea are in no way to be found in us, we rightly conclude that they reside in something distinct from ourselves, namely God – or certainly that they once did so, from which it most evidently follows that they are still there.
René Descartes, Principles of Philosophy (1644).
Kant on the impossibility of an ontological proof of the existence of God
In all ages men have spoken of an absolutely necessary being, and in so doing have endeavored, not so much to understand whether and how a thing of this kind allows even of being thought, but rather to prove its existence. There is, of course, no difficulty in giving a verbal definition of the concept, namely, that it is something the non-existence of which is impossible. But this yields no insight into the conditions which make it necessary to regard the non-existence of a thing as absolutely unthinkable. It is precisely these conditions that we desire to know, in order that we may determine whether or not, in resorting to this concept, we are thinking anything at all. The expedient of removing all those conditions which the understanding indispensably requires in order to regard something as necessary, simply through the introduction of the word unconditioned, is very far from sufficing to show whether I am still thinking anything in the concept of the unconditionally necessary, or perhaps rather nothing at all.
Nay more, this concept, at first ventured upon blindly, and now become so completely familiar, has been supposed to have its meaning exhibited in a number of examples; and on this account all further enquiry into its intelligibility has seemed to be quite needless. Thus the fact that every geometrical proposition, as, for instance, that a triangle has three angles, is absolutely necessary, has been taken as justifying us in speaking of an object which lies entirely outside the sphere of our understanding as if we understood perfectly what it is that we intend to convey by the concept of that object.
All the alleged examples are, without exception, taken from judgments, not from things and their existence. But the unconditioned necessity of judgments is not the same as an absolute necessity of things. The absolute necessity of the judgment is only a conditioned necessity of the thing, or of the predicate in the judgment. The above proposition does not declare that three angles are absolutely necessary, but that, under the condition that there is a triangle (that is, that a triangle is given), three angles will necessarily be found in it.
(…) To posit a triangle, and yet to reject its three angles, is self-contradictory; but there is no contradiction in rejecting the triangle together with its three angles. The same holds true of the concept of an absolutely necessary being. (…) ‘God is omnipotent’ is a necessary judgment. The omnipotence cannot be rejected if we posit a Deity, that is, an infinite being; for the two concepts are identical. But if we say, ‘There is no God’, neither the omnipotence nor any other of its predicates is given; they are one and all rejected together with the subject, and there is therefore not the least contradiction in such a judgment.
(…) I should have hoped to put an end to these idle and fruitless disputations in a direct manner, by an accurate determination of the concept of existence, had I not found that the illusion which is caused by the confusion of a logical with a real predicate (that is, with a predicate which determines a thing) is almost beyond correction. (…)’Being is obviously not a real predicate; that is, it is not a concept of something which could be added to the concept of a thing. It is merely the positing of a thing, or of certain determinations, as existing in themselves. Logically, it is merely the copula of a judgment. The proposition, ‘God is omnipotent’, contains two concepts, each of which has its object – God and omnipotence. The small word ‘is’ adds no new predicate, but only serves to posit the predicate in its relation to the subject. If, now, we take the subject (God) with all its predicates (among which is omnipotence), and say ‘God is’, or ‘There is a God’, we attach no new predicate to the concept of God, but only posit the subject in itself with all its predicates, and indeed posit it as being an object that stands in relation to my concept. The content of both must be one and the same; nothing can have been added to the concept, which expresses merely what is possible, by my thinking its object (through the expression ‘it is’) as given absolutely. Otherwise stated, the real contains no more than the merely possible. A hundred real thalers do not contain the least coin more than a hundred possible thalers. For as the latter signify the concept, and the former the object and the positing of the object, should the former contain more than the latter, my concept would not, in that case, express the whole object, and would not therefore be an adequate concept of it. My financial position is, however, affected very differently by a hundred real thalers than it is by the mere concept of them (that is, of their possibility).
Kant on the impossibility of a cosmological proof of the existence of God
The cosmological proof, which we are now about to examine, retains the connection of absolute necessity with the highest reality, but instead of reasoning, like the former proof, from the highest reality to necessity of existence, it reasons from the previously given unconditioned necessity of some being to the unlimited reality of that being.
(…) This proof, termed by Leibniz the proof a contingentia mundi … runs thus: If anything exists, an absolutely necessary being must also exist. Now I, at least, exist. Therefore an absolutely necessary being exists. The minor premise contains an experience, the major premise the inference from there being any experience at all to the existence of the necessary. The proof therefore really begins with experience, and is not wholly a priori or ontological.
(…) But the cosmological proof uses this experience only for a single step in the argument, namely, to conclude the existence of a necessary being. What properties this being may have, the empirical premise cannot tell us. Reason therefore abandons experience altogether, and endeavors to discover from mere concepts what properties an absolutely necessary being must have, that is, which among all possible things contains in itself the conditions (requisita) essential to absolute necessity.
(…) In this cosmological argument there lies hidden a whole nest of dialectical assumptions, which the transcendental critique can easily detect and · destroy. (…) We find, for instance, the transcendental principle whereby from the contingent we infer a cause. This principle is applicable only in the sensible world; outside that world it has no meaning whatsoever. For the mere intellectual concept of the contingent cannot give rise to any synthetic proposition, such as that of causality. The principle of causality has no meaning and no criterion for its application save only in the sensible world. But in the cosmological proof it is precisely in order to enable us to advance beyond the sensible world that it is employed.
Kant, Critique of Pure Reason (1781, second edition: 1787)
Two modern defenses of the proofs of God’s existence
The classical proofs of God seem suspended between two extremes lying beyond their reach—one in an upward and the other in a downward direction, or one through its richness and the other its poverty—namely: direct intellection and materialistic rationalism; there is nonetheless a sufficiently ample area between these two positions to justify the existence of arguments that aim to set forth evidence for the divine Being in the language of logic. No doubt one can immediately accept the supernatural and have no need of such proofs, Deo juvante, but it shows a lack of sense of proportion and a certain temerity—hardly compatible with true certainty and rather uncharitable toward the needs of others—to look down upon these proofs as if they were valueless in themselves and could have no possible usefulness; such an attitude would in fact be strangely presumptuous, especially since a logical demonstration in favor of the Eternal and of our own final ends always offers some insight and “consolation”, even for those who already possess certainty through intellection or grace.
(…)To be able to accept the ontological proof of God, which deduces the existence of an objective reality from an innate concept corresponding to it, one must begin by understanding that truth does not depend on reasoning—obviously truth is not created by reason—but that it reveals itself or becomes explicit thanks to the key provided by the mental operation; in every act of assent by the Intellect there is an element that escapes the thinking process rather as light and color elude the grasp of geometry, which can nonetheless symbolize them indirectly and remotely. There is no such thing as “pure proof”, for every proof presupposes knowledge of certain data; the ontological proof —formulated in particular by Saint Augustine and Saint Anselm—carries weight for the person who already has at his disposal some initial certainties, but it has no effect upon the willfully and systematically superficial mind. Such a mind no longer understands the profound nature of causality; it regards intelligence as proceeding not from the outward toward the inward but from the inward toward the outward, until it forgets the very reason understanding exists.
As is well known, those who belittle the ontological argument claim that the existence of a notion does not necessarily involve the objective existence of the content of the notion; the answer to this is that it all depends on the nature of the notion in question, for what is plausible in the case of a notion relating to a fact is by no means so in the case of a notion relating to a principle.
The cosmological proof of God, which is found in Aristotle as well as in Plato and which consists in inferring the existence of a transcendent, positive, and infinite Cause from the existence of the world, finds no greater favor in the eyes of those who deny the supernatural. (…) Here again we observe that the objection results from ignoring what is implicit: rationalists forget that at the level in question “proof” is a key or symbol, a means of drawing back a veil rather than of giving light; it is not by itself a leap out of ignorance and into knowledge. The principial argument “indicates” rather than “proves”; it cannot be anything more than a guideline or aide-mémoire, for it is impossible to prove the Absolute outside itself. If to “prove” means to know something only by virtue of a particular mental stratagem—without which one would necessarily remain in ignorance—then there are no possible “proofs of God”, and this explains moreover why one can do without them in symbolist and contemplative metaphysics.
(…) [Apart from the ontological, the cosmological and the teleological or moral proof] there remains the experimental or mystical proof of God. While one must admit that from a strictly logical standpoint and in the absence of doctrine it proves nothing to anyone who has not undergone the unitive experience, there is nonetheless no justification for concluding that it must be false simply because it is incommunicable; this was the error of Kant, who went so far as to give the name “theurgy” to what is simply a direct experience of the divine Substance.
Frithjof Schuon, “Concerning proofs of the existence of God”, Studies in Comparative Religion, Vol. 7, No. 1 (Winter, 1973).
In the Proslogion, Anselm’s analysis is explicit about the limits of the noetic quest. In the second part of his work, in Proslogion XIV, he acknowledges that the God found by the truth of reason is not yet the God whom the seeker has experienced as present in the formation and re-formation of his existence. He prays to God: “Speak to my desirous soul what you are, other than what it has seen, that it may clearly see what it desires.” And in Proslogion XV he formulates the structural issue with classic exactness: “O Lord, you are not only that than which a greater cannot be conceived, but you are also greater than what can be conceived.” This is the limit of the noetic conceptual analysis disregarded by Hegel. (…) The noetic [philosophical] quest of Anselm thus assumes the form of a Prayer for an understanding of the symbols of faith through the human intellect. Behind the quest, and behind the fides the quest is supposed to understand, there now becomes visible the true source of the Anselmian effort in the living desire of the soul to move toward the divine light. The divine reality lets the light of its perfection fall into the soul; the illumination of the soul arouses the awareness of man’s existence as a state of imperfection; and this awareness provokes the human movement in response to the divine appeal. The illumination, as St. Augustine names this experience, has for Anselm indeed the character of an appeal, and even of a counsel and promise. For in order to express the experience of illumination he quotes John 6:24: “Ask, and you will receive, that your joy may be full.” The Johannine words of the Christ, and of the Spirit that counsels in his name, words meant to be understood in their context, express the divine movement to which Anselm responds with the joyful counter-movement of his quest (XXVI). Hence, the latter part of the Proslogion consistently praises the divine light in the analogical language of perfection. Anselm’s Prayer is a meditatio de ratione fidei as he formulates the nature of the quest in the first title of the Monologion. The praying quest responds to the appeal of reason in the fides; the Proslogion is the fides in action, in pursuit of its own reason.
…. But in what sense can Anselm at all connect the term “proof’ with a noetic quest in response to the movement of the Spirit, a quest which he correctly recognizes as a Prayer? The key to the answer is given in the fact that the term does not occur in the Proslogion itself but only in the discussion with Gaunilo. There is no reason why the term should be used in the Proslogion; for when a believer explores the rational structure of his faith the existence of God is not in question. In his answer, however, Anselm must use the term “proof’ because Gaunilo acts the role of the fool, of the insipiens, who says “there is no God” and assumes that the explorer of faith is engaged in a “proof’ for the assertion that God exists. The noetic reflection of the spiritualist acquires the character of an affirmative proposition concerning the existence of God only when confronted by the insipiens who advances the negative proposition that God does not exist. The symbolism of the noetic quest threatens to derail into a quarrel about proof or non-proof of a proposition when the fool enters the discussion. The existence of God can become doubtful because, without a doubt, the fool exists.
The fool cannot be dismissed lightly. The folly of responding to the divine appeal by denial or evasion is just as much a human possibility as the positive response. As a potentiality it is present in every man, including the believer; and in certain historical situations its actualization can become a massive social force.
… One cannot prove reality by a syllogism; one can only point to it and invite the doubter to look. The more or less deliberate confusion of the two meanings of the word “proof’ is still a standard trick employed by the negators in the contemporary ideological debates; and it has played an important role in the genesis of the “proofs” for the existence of God ever since the time of Anselm.
Eric Voegelin, “Quod Deus Dicitur” (1985).