The Five Ways from Summa Theologiae (Part I, Question 2) by Thomas Aquinas (~1265 AD) translated by Brian Shanley (2006) Question 2. Does God Exist? Article 1. Is the existence of God self-evident? It seems that the existence of God is self-evident: 1. Things are said to be self-evident to us when knowledge of them is naturally present in us, as is clear in the case of first principles. But, as Damascene says at the beginning of his book, knowledge of the existence of God is naturally implanted in everyone. Hence the existence of God is self-evident. 2. Things are said to be self-evident that are grasped as soon as the terms are grasped ; for if I know what a whole is and what a part is, then I immediately know that every whole is greater than any of its parts. But if I understand what the name God signifies, then it follows immediately that God exists. For by the name is signified that than which a greater cannot be signified. Now something is greater when it exists both in reality and in the intellect, rather than only in the intellect. Therefore, since when I understand this name God, he immediately exists in the intellect, it follows that God must also exist in reality. Hence the existence of God is selfevident. 3. The existence of truth is self-evident, since someone who denies that there is truth concedes its existence: for if there is no truth, then it is true that there is no truth. But if there is something true, then there must be truth. Now God is Truth itself according to John 16:6: I am the way, the truth, and the life. Hence the existence of God is self-evident. On the contrary. No one can think the opposite of what is self-evident But according to Psalm 53:1 it is possible to think the opposite of God s existing: The fool said in his heart: there is no God. Hence the existence of God is not self-evident. Reply. Something can be self-evident in two ways: first, in itself but not relative to us; second, in itself and relative to us. For a proposition is self-evident when 1
the predicate is included in the definition of the subject, as in the case of A human being is an animal, since animal is part of the definition of human being. Accordingly, if it is known to everyone what the subject is and what the predicate is, then that proposition will be self-evident to everyone If, however, there were people who did not know, regarding the subject or predicate, what it is, then that proposition would be self-evident in itself but not for those who do not grasp its subject and the predicate. Thus it happens, as Boethius says in On the Hebdomads, that some general conceptions of the mind are selfevident only to the wise, such as what is incorporeal does not exist in any place. Hence I say that this proposition God exists is self-evident in itself because the predicate is identical with the subject: for God is his existence, as will later be made clear [I.3.4]. Yet since we do not know what God is, the proposition is not self-evident to us but rather must be demonstrated through what is more evident to us, even if less evident by nature, namely through God s effects. Response to 1. There is a kind of common and confused knowledge of the existence of God naturally implanted within us, namely insofar as God is our happiness. For human beings naturally desire happiness, and what human beings naturally desire they naturally know. But this is not to know in an unqualified way that God exists, just as to know that someone is coming is not the same thing as to know that it is Peter, even though he is the one coming. For many suppose that the perfect human good, happiness, lies in riches, while others suppose it to be found in pleasures or something else. Response to 2. Perhaps someone who hears the name God would not understand it to signify something than which a greater cannot be thought, since some have believed God to be a body. But even if it is granted that everyone understands the name God to signify what the objection says namely that than which a greater cannot be thought nevertheless it does not follow from this that one understands that what is signified by the name exists in the natural order, but rather only in the apprehension of the intellect. Nor can it be argued that it exists in reality unless it were granted that there exists in reality something than which a greater cannot be thought, which would not be granted by those who deny that God exists. Response to 3. The existence of truth in general is self-evident, but that a first truth exists is not self-evident to us. 2
Article 2. Is the existence of God demonstrable? It seems that the existence of God is not demonstrable: 1. That God exists is an article of faith. But what pertains to faith is not demonstrable, because a demonstration produces knowledge, whereas faith concerns what is unseen, as the Apostle Paul says in Hebrews 11:1. Hence the existence of God is not demonstrable. 3. If it were to be demonstrated that God exists, this would be so only through God s effects. Yet God s effects are not proportionate to God, since God is infinite and his effects are finite, and the finite is never proportionate to the infinite. Thus since a cause cannot be demonstrated on the basis of an effect that is disproportionate to it, it seems that the existence of God cannot be demonstrated. On the contrary. The Apostle says in Romans 1:20: The unseen things of God can be grasped through an understanding of what God has made. Yet this would not be so unless it were possible to demonstrate that God exists through what God has made, since the first thing we must understand about anything is whether it exists. Reply. [W]hen an effect is more manifest to us than its cause, we proceed through the effect to a grasp of the cause. Now from any effect we can demonstrate the existence of its proper cause, if its effects are indeed more known relative to us. The reason for this is that, since effects depend upon a cause, if an effect is posited then its cause necessarily preexists. Hence the existence of God, inasmuch as it is not self-evident to us, can be demonstrated through effects that are evident to us. Response to 1. The existence of God and all the other truths about God that can be known through natural reason are not articles of faith, but rather preambles to the articles, as is said in Romans 1:19. For faith presupposes natural cognition in just the way that grace presupposes nature, and in the way that a perfection presupposes what it perfects. Still, nothing prevents what is demonstrable and knowable in itself from being accepted as worthy of belief by someone who does not grasp the demonstration. Response to 3. From effects disproportionate to their causes, it is not possible to derive a perfect grasp of the cause. But from any effect it is possible for us to demonstrate manifestly the existence of its cause, as was noted. Thus from the effects of God it can be demonstrated that God exists, although by means of such effects we cannot perfectly grasp God according to his essence. 3
It seems that God does not exist: Article 3. Does God exist? 1. If one of two contraries were infinite, the other would be totally destroyed. But it is understood by the name God that God is some kind of infinite good. Hence if God existed, then no evil would be found. But evil is found in the world. Thus God does not exist. 2. What can be accomplished through fewer principles is not brought about through more. But it seems that all natural phenomena can be accomplished through other principles when it is assumed that God does not exist. For things that are natural are reducible to the principle that is nature, whereas things that happen by design are reducible to a principle that is human reason or will. Hence it is not necessary to posit the existence of God. On the contrary is what is said in Exodus 3:14 in the person of God: I am who am. Reply. The existence of God can be proved in five ways. The first and more evident way is drawn from motion. For it is certain and firmly established by the senses that some things in this world are moved. Now whatever is moved is moved by another. For something is moved only insofar as it is in potentiality with respect to that toward which it is moved, whereas something moves another insofar as it is in actuality. For to move another is nothing other than to bring something from potentiality to actuality. But something can be brought from potentiality to actuality only through some being in actuality. For example, something actually hot, such as fire, makes wood, which is hot in potentiality, be actually hot, and so moves and alters it. Now it is not possible that the same thing be both in actuality and in potentiality at the same time and in the same respect, but rather only in different respects; for what is actually hot cannot at the same time be potentially hot, but it is at the same time potentially cold. Hence it is impossible that something be both mover and moved in the same respect and in the same way, or that it move itself. Thus whatever is moved must be moved by another. Therefore, if the source of motion is itself moved, then it must itself be moved by another, and this latter by another. Yet this [kind of a causal chain] cannot proceed infinitely because then there would not be something that is a first mover and consequently no other movers at all, since secondary [or moved] movers can move only insofar as they are moved by a first mover, just as a stick moves another only because it is moved by the hand. Therefore, it is necessary to arrive at some first mover that is not put in motion by anything, and this all understand to be God. 4
The second way is from the nature of efficient causes. For we find that there is an order of efficient causes among sensible things. But we neither find nor is it possible for something to be the efficient cause of itself; for then it would be prior to itself, which is impossible. Now it is not possible to proceed infinitely among efficient causes. The reason is that, in any ordered series of efficient causes, the first is the cause of the intermediary and the intermediary causes the last, whether the intermediaries are many or only one. But if you take away the cause, you take away the effect. Hence if there were not a first efficient cause, then there would not be either an intermediate cause or a last cause. But if the series of efficient causes were to proceed infinitely, then there would be no first efficient cause and thus no last effect or intermediate efficient causes, which is obviously false. Therefore, it is necessary to posit some first efficient cause, which everyone names God. The third way is taken from the possible and the necessary, and goes like this: We find that some things are possible with respect to existence or nonexistence, since they are found to be generated and corrupted and consequently possible with respect to existence or nonexistence. But it is impossible for all things that exist to exist like this, for that which can possibly not exist does not exist at some time. Accordingly if all things are possible with respect to nonexistence, then at some time there would have been nothing in reality. But if this were true then there would also be nothing now, because what is not does not begin to be except through something that is. Accordingly, if no being had existed, it would have been impossible for anything to have begun to exist, and thus there would be nothing now, which is patently false. Hence not all beings are possible, but rather it is required that there be something necessary in reality. Now every necessary being either has the cause of its necessity from another or not. But it is not possible to proceed infinitely in a series of necessary beings that have a cause of their necessity, as was just proven in the case of efficient causes. Therefore, it is necessary to posit something that is necessary through itself, something that does not have the cause of its necessity from another, but that is the cause of necessity for the others. This is what everyone calls God. The fourth way is taken from the gradation to be found among things. For we find among things one that is more or less good than another, more or less true, more or less noble, and so on with other perfections like these. But more or less is said about diverse things insofar as they approach in their diverse ways something that is the maximum, as in the case where something is hotter the more it approaches what is maximally hot. Accordingly there is something that is truest, best, noblest, and consequently greatest in being, for whatever is truest is also greatest in being, as said in Metaphysics II. Now whatever is said to be maximally such in any genus is the cause of everything else in the genus; 5
for instance fire, which is maximally hot, is the cause of all other instances of heat, as is said in the same book. Therefore, there must be something that is, for everything else, the cause of its existence, goodness, and every other perfection, and this we call God. The fifth way is taken from the governance of things. For we see some things that lack cognition, namely natural bodies, act for the sake of some end. This is apparent from the fact that they always or most often act in the same way so as to attain what is best. From this it is obvious that they achieve their end not by chance but by intention. But those things that lack cognition do not tend toward an end except under the direction of something cognitive and intelligent, as in the case of an arrow from an archer. Therefore, there is some intelligent being by whom all natural things are ordered to an end, and this we call God. Response to 1. As Augustine says in his Enchiridion: God, since he is supremely good, would never have allowed anything evil in his works unless he were so omnipotent and good that he could bring forth good even from evil. Hence it pertains to the infinite goodness of God that God allow evils and from them bring forth goods. Response to 2. Since nature acts for the sake of a determinate end by the direction of some superior agent, it is necessary that whatever happens naturally be reduced to God as first cause. Similarly, whatever happens by design must also be reduced back to a higher cause, which is not human reason and will, since these are changeable and fallible. For it is necessary, as was shown, that all mutable and fallible beings be reduced to some first principle that is immutable and necessary through itself. 6