Peter Kreeft

The First Cause Argument

If there is no first cause, then the universe is like a great chain with many links; each link is held up by the link above it, but the whole chain is held up by nothing.

The most famous of all arguments for the existence of God are the "five ways" of Saint Thomas Aquinas. One of the five ways, the fifth, is the argument from design, which we looked at in the last essay. The other four are versions of the first-cause argument, which we explore here.

The argument is basically very simple, natural, intuitive, and commonsensical. We have to become complex and clever in order to doubt or dispute it. It is based on an instinct of mind that we all share: the instinct that says everything needs an explanation. Nothing just is without a reason why it is. Everything that is has some adequate or sufficient reason why it is.

Philosophers call this the Principle of Sufficient Reason. We use it every day, in common sense and in science as well as in philosophy and theology. If we saw a rabbit suddenly appear on an empty table, we would not blandly say, "Hi, rabbit. You came from nowhere, didn't you?" No, we would look for a cause, assuming there has to be one. Did the rabbit fall from the ceiling? Did a magician put it there when we weren't looking? If there seems to be no physical cause, we look for a psychological cause: perhaps someone hypnotized us. As a last resort, we look for a supernatural cause, a miracle. But there must be some cause. We never deny the Principle of Sufficient Reason itself. No one believes the Pop Theory: that things just pop into existence for no reason at all. Perhaps we will never find the cause, but there must be a cause for everything that comes into existence.

If there is no first cause, then the universe is like a great chain with many links; each link is held up by the link above it, but the whole chain is held up by nothing.

Now the whole universe is a vast, interlocking chain of things that come into existence. Each of these things must therefore have a cause. My parents caused me, my grandparents caused them, et cetera. But it is not that simple. I would not be here without billions of causes, from the Big Bang through the cooling of the galaxies and the evolution of the protein molecule to the marriages of my ancestors. The universe is a vast and complex chain of causes. But does the universe as a whole have a cause? Is there a first cause, an uncaused cause, a transcendent cause of the whole chain of causes? If not, then there is an infinite regress of causes, with no first link in the great cosmic chain. If so, then there is an eternal, necessary, independent, self-explanatory being with nothing above it, before it, or supporting it. It would have to explain itself as well as everything else, for if it needed something else as its explanation, its reason, its cause, then it would not be the first and uncaused cause. Such a being would have to be God, of course. If we can prove there is such a first cause, we will have proved there is a God.

Why must there be a first cause? Because if there isn't, then the whole universe is unexplained, and we have violated our Principle of Sufficient Reason for everything. If there is no first cause, each particular thing in the universe is explained in the short run, or proximately, by some other thing, but nothing is explained in the long run, or ultimately, and the universe as a whole is not explained. Everyone and everything says in turn, "Don't look to me for the final explanation. I'm just an instrument. Something else caused me." If that's all there is, then we have an endless passing of the buck. God is the one who says, "The buck stops here."

If there is no first cause, then the universe is like a great chain with many links; each link is held up by the link above it, but the whole chain is held up by nothing. If there is no first cause, then the universe is like a railroad train moving without an engine. Each car's motion is explained proximately by the motion of the car in front of it: the caboose moves because the boxcar pulls it, the boxcar moves because the cattle car pulls it, et cetera. But there is no engine to pull the first car and the whole train. That would be impossible, of course. But that is what the universe is like if there is no first cause: impossible.

Here is one more analogy. Suppose I tell you there is a book that explains everything you want explained. You want that book very much. You ask me whether I have it. I say no, I have to get it from my wife. Does she have it? No, she has to get it from a neighbor. Does he have it? No, he has to get it from his teacher, who has to get it. . . et cetera, etcetera, ad infinitum. No one actually has the book. In that case, you will never get it. However long or short the chain of book borrowers may be, you will get the book only if someone actually has it and does not have to borrow it. Well, existence is like that book. Existence is handed down the chain of causes, from cause to effect. If there is no first cause, no being who is eternal and self-sufficient, no being who has existence by his own nature and does not have to borrow it from someone else, then the gift of existence can never be passed down the chain to others, and no one will ever get it. But we did get it. We exist. We got the gift of existence from our causes, down the chain, and so did every actual being in the universe, from atoms to archangels. Therefore there must be a first cause of existence, a God.

If there is no independent being, then the whole chain of dependent beings is dependent on nothing and could not exist.

In more abstract philosophical language, the proof goes this way. Every being that exists either exists by itself, by its own essence or nature, or it does not exist by itself. If it exists by its own essence, then it exists necessarily and eternally, and explains itself. It cannot not exist, as a triangle cannot not have three sides. If, on the other hand, a being exists but not by its own essence, then it needs a cause, a reason outside itself for its existence. Because it does not explain itself, something else must explain it. Beings whose essence does not contain the reason for their existence, beings that need causes, are called contingent, or dependent, beings. A being whose essence is to exist is called a necessary being. The universe contains only contingent beings. God would be the only necessary being—if God existed. Does he? Does a necessary being exist? Here is the proof that it does. Dependent beings cannot cause themselves. They are dependent on their causes. If there is no independent being, then the whole chain of dependent beings is dependent on nothing and could not exist. But they do exist. Therefore there is an independent being.

Saint Thomas has four versions of this basic argument.

There is a single common logical structure to all four proofs. Instead of proving God directly, they prove him indirectly, by refuting atheism. Either there is a first cause or not. The proofs look at "not" and refute it, leaving the only other possibility, that God is.

Each of the four ways makes the same point for four different kinds of cause: first, cause of motion; second, cause of a beginning to existence; third, cause of present existence; and fourth, cause of goodness or value. The common point is that if there were no first cause, there could be no second causes, and there are second causes (moved movers, caused causers, dependent and mortal beings, and less-than-wholly-perfect beings). Therefore there must be a first cause of motion, beginning, existence, and perfection.

How can anyone squirm out of this tight logic? Here are four ways in which different philosophers try.

If this argument is getting too tricky, the thing to do is to return to what is sure and clear: the intuitive point we began with. Not everyone can understand all the abstract details of the first-cause argument, but anyone can understand its basic point: as C. S. Lewis put it, "I felt in my bones that this universe does not explain itself."


From Fundamentals of the Faith by Ignatius Press.

This text is also available as an audio lecture under:
Arguments for God's Existence