Five Ways to Prove the Existence of God From Summa Theologica St. Thomas Aquinas
Thomas Aquinas (1225 1274), born near Naples, was the most influential philosopher of the medieval period. He joined the Dominican order and taught at the University of Paris. In his vast writings, composed in Latin, he sought to demonstrate that Christian belief was consistent with reason. Aquinas greatest, and best-known, work was the Summa Theologica. We will read further excerpts from the Summa when we begin discussing Philosophy of Economics. The Summa is one of the classics of the history of philosophy and one of the most influential works of Western literature. Intended as an instructional guide for theology students, the Summa is a compendium of all of the main theological teachings of the Catholic Church, and it presents both an articulation and a defense of almost all the important points of Christian theology in the West. The most famous passage of the Summa, printed here, is the five ways to prove the existence of God. While Aquinas believed that not all the tenets of Christian doctrine could be demonstrated without reliance on Divine Revelation, he did maintain that the existence of God was provable without any appeal to faith. In the fourth way (i.e., proof) Aquinas cites Metaphysics II. The reference is to the second book of Metaphysics of Aristotle, and serves as a reminder of Aquinas s regard for that highly influential Greek thinker. We will only examine a few of the proofs in this reading. 1
The Five ways The existence of God can be proved in five ways. 1 2. The second way is from the nature of the efficient cause. In the world of sensible things, we find that there is an order of efficient causes 2. There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself, insofar as this would require a thing to be prior to its own existence, which is impossible. Now, for 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 only one. 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 it is possible for efficient causes 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 this is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God. Summary of Argument from Efficient Causes 1 These five are not the proofs themselves, but ways, i.e., indications or summaries of proofs. The proofs themselves are elsewhere worked out in much greater detail. The first proof is not included here. 2 As you should recall from the Aristotle reading, the efficient cause can be thought of as the what-actually-does-or-make-it? cause. It has to do with the agent, or force, that brings a thing into being or initiates a change. 2
1. We perceive a series of efficient causes of things in the world. 2. Nothing exists prior to itself. 3. Therefore nothing [in the world of things we perceive] is the efficient cause of itself. 4. If a previous efficient cause does not exist, neither does the thing that results from the cause (the effect). 5. Therefore if the first thing in a series does not exist, nothing in the series exists. 6. If the series of efficient causes extends infinitely into the past, then there would be no things existing now. 7. That is plainly false (i.e., there are things existing now that came about through efficient causes). 8. Therefore efficient causes do not extend ad infinitum into the past. 9. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God. 3. The third way is taken from possibility and necessity and runs thus. We find in nature things that are possible to be and possible not to be, since they are found to be generated, and to decay. Consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which can not-be at some time is not. Therefore, if everything can not-be that is, if non-being is a possibility for everything that exists then at one time there was nothing in existence. Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing. Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence which is absurd. 3
Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their necessity caused by another, as has been already proved in regard to efficient causes. Therefore we must postulate the existence of some being that has, of itself, its own necessity, and not receiving it from another, but rather causing in others their necessity. This all men speak of as God. Summary of Argument from Possibility and Necessity (Reductio ad Absurdum) 1. We find in nature things that are possible to be and possible not to be: i.e., things that come into being and go out of being. These are called contingent beings. 2. Assume that every being is a contingent being. 3. For each contingent being, there is a time that it does not exist. 4. Therefore, it is impossible for these contingent beings always to exist. 5. Therefore, there could have been a time when no things existed. 6. Therefore, at that time, there would have been nothing to bring the currently existing contingent beings into existence. 7. Therefore, nothing would be in existence now. 8. We have reached an absurd result from assuming that every being is a contingent being. 9. Therefore, not every being is a contingent being. 10. Therefore, some being exists of its own necessity and does not receive its existence from another being, but rather causes them. All men speak of as God as this necessary being. 4. The fourth way is taken from the gradation to be found in things. 4
Among beings there are some more good and some less good, some are more true and some less true, some are more noble and some are less noble and the like. But more and less are predicated of different things, according to the extent that they resemble, in their different ways, something which is the maximum (or the perfect standard). That is, a thing is said to be hotter according to the extent to which it more nearly resembles that which is hottest. So, there is therefore something which is truest, something best, something noblest and, consequently, there is something which has the most being. For those things that are greatest in truth are greatest in being, as it is written in Metaphysics II. Now, the maximum in any genus is the cause of all in that genus as fire, which is the maximum heat, is the cause of all hot things. Therefore, there must also be something which is to all beings the cause of their being, of their goodness, and of every other perfection we attribute to them. And this we call God. Summary of Argument from the Gradation of Being 1. There is a gradation to be found in things: some are better or worse than others. 2. Predications of degree require reference to the uttermost case (e.g., a thing is said to be hotter than other thing insofar as it more nearly resembles that which is hottest; a thing is said to be more virtuous than another things insofar as it more closely approaches perfect virtue ). 3. The maximum in any genus is the cause of all in that genus. 4. Therefore, there must also be something which is to all beings the cause of their being, the cause of their goodness, and the cause of every other perfection. And this we call God. 5. The fifth way is taken from the governance of the world (also Called the Teleological Argument). 5
We see that things which lack intelligence, such as natural bodies, act (move or develop) for the sake of an end, or a goal, or a purpose [i.e., a telos]. And this is evident from their acting always, or nearly always, in the same way, so as to obtain the best result. Hence, it is plain that not fortuitously, but by virtue of design, do things achieve their purpose or goals. Now, whatever lacks intelligence cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence as the arrow is shot to its mark by the archer. Therefore some intelligent being exists by whom all natural things are directed to their end. And this being we call God. Summary: Argument from Design. We see that natural bodies work toward some goal, and do not do so by chance. 2. Most natural things lack knowledge. 3. But as an arrow reaches its target because it is directed by an archer, what lacks intelligence achieves goals by being directed by something intelligence. 4. Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God. The Argument from Design is probably the most popular (or well-known) argument for the existence of God. It can also be called the teleological argument for God s existence. The argument often runs like this: As we look at the world around us, and ourselves, we see ample evidence of design the bird's wing, designed for the purpose of flight; the human ear, designed for the purpose of hearing; the natural environment, designed to support life; and on and on. If there is design, there must be a designer. Naturally, God is that designer. 6
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 it is possible for efficient causes 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 this is plainly false. Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God 7