Thomas Aquinas: High Middle Ages (1225–1274)

Whether God Exists? (I.2.3)

Objection 1. It seems that God does not exist; because if one of two contraries be infinite, the other would be altogether destroyed. But the word “God” means that He is infinite goodness. If, therefore, God existed, there would be no evil discoverable; but there is evil in the world. Therefore God does not exist.

Objection 2. Further, it is superfluous to suppose that what can be accounted for by a few principles has been produced by many. But it seems that everything we see in the world can be accounted for by other principles, supposing God did not exist. For all natural things can be reduced to one principle which is nature; and all voluntary things can be reduced to one principle which is human reason, or will. Therefore there is no need to suppose God’s existence.

On the contrary, It is said in the person of God: “I am Who I am” (Ex. 3:14).

I answer that, The existence of God can be proved in five ways.

The first and more manifest way is the argument from motion. It is certain, and evident to our senses, that in the world some things are in motion. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act.

For motion is nothing else than the reduction of something from potentiality to actuality. But nothing can be reduced from potentiality to actuality, except by something in a state of actuality. Thus that which is actually hot, as fire, makes wood, which is potentially hot, to be actually hot, and thereby moves and changes it. Now it is not possible that the same thing should be at once in actuality and potentiality in the same respect, but only in different respects. For what is actually hot cannot simultaneously be potentially hot; but it is simultaneously potentially cold. It is therefore impossible that in the same respect and in the same way a thing should be both mover and moved, i.e. that it should move itself. Therefore, whatever is in motion must be put in motion by another.

If that by which it is put in motion be itself put in motion, then this also must needs be put in motion by another, and that by another again. But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand.

Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

The second way is from the nature of the efficient cause. In the world of sense 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 only one.

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, and runs thus. We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be. But it is impossible for these always to exist, for that which is possible not to be at some time is not. Therefore, if everything is possible not to be, then at one time there could have been 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.

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 cannot but postulate the existence of some being having 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.

The fourth way is taken from the gradation to be found in things. Among beings there are some more and some less good, true, noble and the like. But “more” and “less” are predicated of different things, according as they resemble in their different ways something which is the maximum, as a thing is said to be hotter according as it more nearly resembles that which is hottest; so that there is something which is truest, something best, something noblest and, consequently, something which is uttermost being; for those things that are greatest in truth are greatest in being. . . . 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, goodness, and every other perfection; and this we call God.

The fifth way is taken from the governance of the world. We see that things which lack intelligence, such as natural bodies, act for an end, 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 designedly, do they achieve their end. 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.

Reply to Objection 1. As Augustine says (Enchir. xi): “Since God is the highest good, He would not allow any evil to exist in His works, unless His omnipotence and goodness were such as to bring good even out of evil.” This is part of the infinite goodness of God, that He should allow evil to exist, and out of it produce good.

Reply to Objection 2. Since nature works for a determinate end under the direction of a higher agent, whatever is done by nature must needs be traced back to God, as to its first cause. So also whatever is done voluntarily must also be traced back to some higher cause other than human reason or will, since these can change or fail; for all things that are changeable and capable of defect must be traced back to an immovable and self-necessary first principle, as was shown in the body of the Article.

According to Augustine in On Christian Doctrine , one skilled in speech should “so speak as to teach, to delight, and to change; that is, to teach the ignorant, to delight the bored and to change the lazy.” To that hopeful end, the first words that Thomas Aquinas spoke in his inaugural sermon as a newly minted Master of Theology were from Augustine’s work. In the days and years to come however, where Augustine synthesized rhetorical and theological styles, Aquinas separated them.

In his book European Literature and the Latin Middle Ages, Ernst Robert Curtius writes “This rhetorical-theological divide was implicit in the Aristotelian distinction between rhetoric (the art of persuasion) and dialectic (the art of reasoning) that became explicit when theology was declared a “science” and elevated beyond the liberal arts.” Aquinas is not casual reading.

John Mark Reynolds, writing in his book The Great Books Reader adds:

Thomas, of all men, knew that sacred and secular must come together in the beating heart of man as created in the image of God. He lived as he thought, and his hymns are as beautiful as his philosophy is profound.

Argue with Thomas, because that is what he wants you to do, but follow his argument carefully, for it is very subtle. Few readers, perhaps, will agree with everything he says—even the Church of Rome does not—but it’s always worth considering.

Once you get the trick of reading Thomas, he is easy to “get” but also hard to exhaust. His argument is clear, but it’s also subtle, and what seems like an obvious problem will be filled in later or is anticipated in his careful wording.

How do you force yourself to read slowly and deliberately when the text requires it?  Is this difficult for you?

Join the discussion on Facebook HERE 


John 1:1

In the beginning was the Word, and the Word was with God, and the Word was God.



John Mark Reynolds is the president of The Saint Constantine School, a school that aspires to preschool through college education. He is also a philosopher, administrator, and joyous curmudgeon. Reynolds was the founder and first director of the Torrey Honors Institute at Biola University. He was provost at Houston Baptist University where he was instrumental in starting the graduate Apologetics program and a cinema and new media arts major. John Mark blogs at Eidos on the Patheos Evangelical platform and has written for First Things and the Washington Post. He is an owner of the Green Bay Packers.


D I G  D E E P E R

The Truth of Saint Thomas Aquinas

Peter Kreeft

I am totally convinced that Saint Thomas Aquinas was the greatest, wisest, most intelligent merely human theologian who ever lived.

Why? Let the first reason be that he told the truth. Nothing trumps that.

Second, he’s the master of common sense. What he says is always what sound reason says, even though he says it in his difficult, technical, medieval-Aristotelian vocabulary. G. K. Chesterton’s Saint Thomas Aquinas: The Dumb Ox proves this brilliantly.

Third, he was not just a head but a heart: a saint and a practical man. Kings, peasants, and popes wrote to him for advice and always got back sound wisdom. (Example: his cure for depression—a hot bath, a glass of wine, and a good night’s sleep.)

Fourth, he combined the two essential goals of thinking better than anyone else: profundity and clarity. He wrote about the most difficult and profound questions a man can ask: God and man, good and evil, life and death, virtue and vice, soul and body, intellect and will, predestination and free will, nature and grace—and he did it clearly and simply. Though at first he seems difficult, he becomes amazingly straightforward and simple on subsequent readings, once the vocabulary obstacle is overcome. He is a transparent window; there are no impositions of his personality, no rhetorical tricks, no extra words, no digressions, all bottom-line, right-to-the-point answers, and always with compelling logical reasons.

Fifth, he fulfilled more than anyone else the essential medieval program of a marriage of faith and reason, revelation and philosophy, the biblical and the classical inheritances. He “baptized” philosophy, especially Aristotle. He did not turn the Christian faith into a purely rational philosophy; he turned Aristotle’s purely rational philosophy into a servant of Christian faith.

Sixth, he also combined elaborate, careful detail with “the big picture,” his cosmic perspective, which is breathtakingly big.


Thomas Aquinas wrote many thousands of pages in addition to his unfinished four-thousand-page masterpiece, the Summa Theologiae, which he dictated to four secretaries at once, sentence by sentence, never changing a word. Then he stopped writing and called everything he had ever written “straw” compared with “what has been revealed to me” (or, in another account, “what I have seen”). His fellow monks heard a heavenly voice ask him, “You have written well of Me, Thomas, what will you have as your reward,” and heard his absolutely perfect, absolutely simple answer: “Only Thyself, Lord.” Never was more said in fewer words.

By the way, Protestants and Anglicans and even agnostics often love and respect Thomas as much as Catholics do. Certainly, there was no greater thinker for two thousand years between the death of Aristotle and the publication of Descartes’ Discourse on Method (except perhaps Augustine). Whoever you are, your mind will get a wonderful workout in clarity and logic, as well as orthodox theology, by reading him.

Reading Thomas Aquinas is like eating spinach. It tastes strange at first, but it makes you stronger. His habits of clarity and order rub off on you, even when you disagree with him.

Nevertheless, read him slowly. The Summa is not a novel but a reference book.

Furthermore, Summa is an ordered summary, not a closed system. Its structural outline is a mirror of reality. It begins in God, “in the beginning,” then proceeds to the act of Creation and God’s continuing providence in dealing with creatures, centering on man, who alone is created in God’s image; it ends with man’s return to God, his end, through his moral and religious life, and finally man’s means to this end of salvation, namely Christ, who saves man through His body and His church (which is His body). It’s the universal drama of God as Alpha and Omega of all time and change. God pumps the blood of being through the arteries of creation into the body of the universe, which wears a human face, and receives it back through the veins of man’s life of free choice of faith, hope, and love. This is a cosmic circulatory system.


It’s good to be aware that, though logically outlined into many sub, sub-sub, and sub-sub-subdivisions, the basic unit of the Summa is the “article,” typically a page or two long, which has five structural parts:

1. The question is formulated in a yes or no format, beginning with “Whether . . .”

2. Objections to his answer are given, fairly and clearly and completely, beginning with “It seems that . . .”

3. An argument from a past authority is given, with the formula “On the contrary . . .”

4. The body of the article, beginning with “I answer that . . .” is his main proof for his position, with explanations along the way.

5. Finally, each objection is answered, usually by distinguishing what is true and what is false in it.

This is no merely local and quaint medieval format. Not one of these steps can ever be omitted if we want to have good grounds for settling any controversial question.


Thomas Aquinas is scrupulously fair. Though his prosaic, literal, bottom-line logical style is an extreme contrast to Augustine’s charming, rambling, and singing poetry, his single-minded, pure passion for truth is strikingly similar. Neither of them seems even capable of dishonesty.

If you were a CIA agent recruiting among philosophers for spies, no two would be more hopelessly inept than these.

Peter Kreeft, PhD, is a professor of Philosophy at Boston College and The King’s College, New York. He is an acclaimed author and speaker on many philosophical and theological topics.

John Mark Reynolds, The Great Books Reader: Excerpts and Essays on the Most Influential Books in Western Civilization (Grand Rapids, MI: Bethany House, 2011).