Description
St. Thomas Aquinas’ best known work is his “five ways” of proving that God exists. Laid out in his masterpiece, the Summa Theologica, they are curt, informal, and scantily defended. Despite what many think, they are not even apologetics, as the Summa was written for priests. The “proper” use of the five ways is deepening the understanding of people who already believe in God.
Let me be clear: I do not believe the five ways are outdated, I do believe they are sound arguments, and they do have modern philosophical proponents. However, even when fleshed out, I do not believe they are the best apologetic resource. It is much better to use a variation of the third way, such as mine here, as it is complete, proves everything which needs to be proven, and is the simplest option. If you are trying to prove God’s existence to a skeptic, it is best not to use five disparate, complex arguments when one is totally sufficient.
If you would like to read St. Thomas’ own “formal” apologetics, they are here in the Contra Gentiles. Of course, St. Thomas, living in the 13th century, failed to directly address quantum physics. For that, you can read Nigel Cundy, a physics professor and Thomist. He wrote a book on the subject called What is Physics? A Defense of Classical Theism. He has a blog and sometimes does video interviews as well. Obviously, I don’t think a thorough understanding of quantum physics is in any way necessary to prove God’s existence, nor to comprehend the five ways. These resources are for the sake of more thorough understanding, or recreation.
As for the topic of this page: the five ways are indeed an excellent tool for understanding the concept of God. My goal is to briefly describe the true meaning of each argument, as well as provide the unifying principles which develop the series into one coherent whole. All credit to Dr. Gaven Kerr for his work revealing the “common thread” of the per se and per aliud in each argument.
The First Way
“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.”
Explanation
The first step to understanding this argument is to understand the Aristotelian meanings of “potential” and “actual.” This is where most of the confusion around this argument comes from. People assume this is referring to some sort of Newtonian potential energy, but it is not. At all. “Potency” is a shorthand reference to the law of noncontradiction: a cup of coffee which is actually 75° is “potentially” 70° because it cannot actually be 75° and 70° at the same time. One might say that the cup is not actually any one temperature, but is the average of many molecules. Sure, but this only pushes the issue down to the molecular level rather than addressing it. The idea of potency and actuality is simply that no being can be in two contradictory states at once.
Even at the furthest reaches of modern science, this idea remains obviously true. Can a particle both be in a state of spontaneous emission and not in a state of spontaneous emission at once? Prior to the Big Bang, when time did not exist, could a wave function both be emitting a particle and not emitting a particle? Could the Big Bang both be happening and not happening at the same time? Obviously, the answer to these is no. This is all that Aristotle claims in drawing the distinction between potency and act.
Now these terms should illuminate the Aristotelian meaning of the word “motion.” Again, this does not refer to some Newtonian concept of an object literally moving from point A to point B. “Motion” describes beings going from a state of potency to a state of actuality. That is, the coffee cup moving from cold to hot. Or a subatomic particle going from “not-emitted” to “emitted.”
With these two simple premises understood, we can understand St. Thomas’s next point. Nothing can actualize itself, for that would require being in the actual state prior to being in the actual state, which is obviously impossible. Thus, if a being is changing from potential to actual, it can only be by the power of another. But if all beings required the motion of another to precede them, nothing could ever change! Imagine plugging a TV into a power strip, and then that power strip into another, and that into another – the TV would never turn on. So how is it that things actually change?
St. Thomas’ answer is a simple distinction: per se and per aliud. When a being has a quality per se, it has it “of itself.” Imagine fire. Despite all of the inputs to a fire not being hot – wood, matches, kindling – fire is hot. Thus, fire has heat “of itself,” part of its nature. When a being has a quality per aliud, it has it “of another.” So, if I use a fire to heat a pot of water, the water has heat “of another.” St. Thomas uses this principle to answer the problem of infinite regression: one being must have actuality per se, the way fire has heat per se. That is, this being is complete in every conceivable way, with no potency whatsoever. This means infinite power to actualize without requiring a prior actualizer. A “first mover.”
Aquinas says that the fully actual being, or “first mover” must be God. He proves this in successive chapters, but I will give a brief look into how he does it:
There can only be one fully actual being, for any distinction from pure actuality is potency. A fully actual being cannot be material, because material always has potency – so He is immaterial. He must be eternal, for if He wasn’t, something would have to have moved Him from potential existence to actual existence. He must be perfect – that is, lacking in absolutely nothing, for any lack denotes unfulfilled potential. This means He is omnibenevolent, having all that is desirable innately. What is fully actual acts upon others without ever being acted upon, and since that is the principle of all motion, He is all-powerful. He must know all things, for if He did not know something, He would have potential to know it. And so on and so on.
The Second Way
“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.”
Explanation
The first step to understanding this deceptively simple argument is to understand “efficient causes.” There are two types of causal chains: accidental and efficient. An accidental series is a series of independent beings. For example, a man has a son, and then he has a son, and so on. These chains, St. Thomas allows, could go on forever. But an “efficient cause” denotes a simultaneous regression, in which each step continuously depends on the prior. For example, you are composed of organs, and those organs are composed of cells, and they of molecules, and they of atoms, and so on. Or, you are alive because the sun heats the earth, but the sun’s heat comes from nuclear reactions, and those from atoms, those from subatomic particles, and those from Higgs-Boson particles, and so on. If any part of these chains ceased to cause the next, you would cease to exist.
Note that the sun ceasing to exist would not immediately kill you, but is still an efficient cause. Efficient causes are logical regressions, not temporal ones. You depend on the sun just as much as you depend on the cells of your body.
Now, this argument simply points out that simultaneous regressions can’t go on forever. Again, an infinite series of power strips could never turn on a TV. The answer to this infinite regression is the same as the previous one: God has the power of cause per se, innate to His own being. All other beings have the power to cause things per aliud, derived from God as the first principle. So this argument is not saying God “started” the universe and the universe sort of carries on without Him. To the contrary, God is ever-present to all things as the ultimate efficient cause. He is the continual, sustaining, uncaused power behind all things.
The Third Way
“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.”
Explanation
St. Thomas begins by pointing out that some beings are “possible” – that is, they are generated and they corrupt. By definition, anything which is generated and corrupts must at some point not exist. Consider yourself – you did not exist for billions of years. Therefore, if all beings were possible beings, then nothing could exist at all, for there would be nothing there to create the first generation. But of course, this cannot be, since we see that possible beings obviously do exist right now. As such, some being must be necessary, as opposed to merely possible.
Now St. Thomas does not mean “necessary” the way some of his philosophical successors mean it. “Necessary” to St. Thomas simply means “a being who can’t fail to exist once it exists.” So this would include the human soul and the angels. But of course, we have already shown that the human soul, despite plausibly being necessary once it exists, still begins to exist. It still had to be created by another. From here, St. Thomas reasons that, like the previous two arguments, the chain cannot go on forever. There cannot be an infinitely long chain of beings passing along a property none of them have. Once again, the only plausible answer is a being which has existence per se, innate to itself. Something simply exists, uncreated.
Why can’t this be an angel or multiple gods? The very idea of a per se quality is that it is part of a being’s essence. So, any being whose existence is distinct from their essence does not have existence per se by definition. As such, there can only be one being who has existence per se. But that being must also necessarily be immaterial, immutable, eternal, and so on and so on.
The Fourth Way
“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, as it is written in Metaph. 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, goodness, and every other perfection; and this we call God.”
Explanation
Despite the apparent complication of this way, it is actually one of the simplest. He begins with an analogy regarding fire. According to 13th century physics, fire is one of the four elements which constitute all things. Although this is obviously an outdated position, we can easily translate the argument to modern parlance by just using “the nature of heat” instead of “fire.” St. Thomas means to point out that only the nature of heat has heat per se, and if there were no such nature, nothing else could have heat. As such, the entire genus (category) of hotness depends on the existence of heat. We can use plenty of other examples of this. The entire genus of “saltiness” depends on salt. Were there no salt, nothing could be salty. The genus of redness depends on red. The genus of woodiness depends on wood.
Next, St. Thomas references Metaphysics II, in which Aristotle argues that a thing has “more truth” the fewer intermediaries it depends on – that is, the closer it approaches to being self-evident. Likewise, he says a being has “more existence” the fewer intermediaries it depends on – that is, the closer it approaches to being self-evident. So, a fox has more being than his shadow, or, a man has more being than his dreams. But of course, this means that being is a genus, so there must be a nature of being per se. A being which exists per se, self-evidently, must be God. This applies to the other transcendental ideas mentioned as well. For example, it is clear that some men are better than Hitler, and therefore there is a genus of goodness.
This argument is probably the least-understood of the ways. Richard Dawkins famously quipped that if these premises are true, there must be something maximally stinky, and this would have to be God. He’s actually half-right – if stinky-ness is a genus, then this does prove there is a nature of stink. Far from countering this argument, it serves as another example (with heat, saltiness, redness, woodiness) of how a genus proves a per se nature. But is God the per se nature of stink? Well, note that St. Thomas did not conclude that God is the hottest thing. This argument in no way suggests that the maximum of every genus is God. He only states that being, truth, nobility, and goodness are geneses, and so have maximums like every other genus. Because God is immaterial and fully actual, these geneses fit His ontology; contrarily, material maximums like saltiness or stinky-ness don’t.
Does this mean that God is the maximum of the genus of evil? “Evil” is just a word to describe the privation of a good which ought to be there. It does not actually “exist” in itself, it is really “un-goodness.” The concept of a genus of evil is as incoherent as a genus of “un-saltiness.”
The Fifth Way
“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.”
Explanation
Another deeply misunderstood argument – this is not a simple case of pointing to the complexity of the universe and saying it must be God. Rather, St. Thomas approaches something more fundamental.
St. Thomas points out that things behave according to set patterns – that is, they have natures. A nature can exist in two ways. Either it is in an object as-is, or it is known by another, like the watchmaker foreknows the nature of the watch. Now consider an acorn transforming into an oak tree. In some sense, the nature of the oak tree must be present to it, otherwise, why become an oak tree? Why not become something random? Or just do nothing? Now the nature of an oak tree cannot be present within an acorn as-is, because an acorn is not itself an oak tree. But neither can it be present to an acorn in the sense of conscious foreknowledge, as an acorn knows nothing. So how is the nature of the oak tree present to the acorn? This is where St. Thomas draws the analogy of the archer.
Imagine you were standing next to a target and suddenly an arrow flew into it. There’s a chance that may have just been some random cosmic occurrence. But now imagine more and more arrows fly uniformly into the target. Now imagine billions of arrows fly into the target. Now imagine billions of arrows fly into that target as well as 500 other targets nearby. The only reasonable explanation is that a mind is directing the arrows to their respective targets. Similarly, an acorn cannot consciously self-direct to its end state as an oak tree, so upon seeing the uniformity with which acorns become oak trees, one must surmise there is a mind behind it.
Now, one may point to evolution or the laws of nature as an explanation for this. But a law is an anthropomorphic thing; we have become so accustomed to using it to describe nature that we forget nature does not actually “obey” laws. Calling something a “law of nature” does absolutely nothing to explain it. As C.S. Lewis put it, “to say that a stone falls to the earth because it’s obeying a law makes it a man and even a citizen.”
To reiterate, this is not a teleological argument pointing out the complexity of nature. It is simply pointing out the coherence of nature, and that without mind, there’s no reason to expect any coherence whatsoever. Life could be a lot more like Alice in Wonderland. The fundamental idea is that God has coherence per se, while all other beings have coherence per aliud. Even conscious beings are (in a sense) like “arrows” relative to God, as He is the principle of order and regularity upon which even conscious minds depend.
Conclusion
The five ways follow a series of per se and per aliud distinctions. The first per se is actuality, which is the ability to move beings from one state into another. God has no potential within Himself – He is fully actual, completely independent and self-sufficient. Second, causality itself belongs to God. He is the principle by which all intermediate causes receive their power. Third, existence belongs to God. God is existence, and any other existing being is participating in God’s true existence. Fourth, God is the maximum of the transcendental goods – He is completeness, is goodness, is nobility, is truth, and so on. He is the maximum of all that men aspire to. Fifth, God is the cohering principle of existence. He communicates coherence to all things per their natures. The stars obey without awareness by physical laws; animals obey by instinct; man obeys by comprehending and loving God.
We see from the five ways that God is the alpha and the omega. He is the provider, and His provisions all lead back to Him as the ultimate final cause. All things seek God, whether consciously or unconsciously. Even the atheist who passionately seeks justice seeks the maximum in the genus of justice, which is God. And furthermore, justice itself is a form of coherence, which is what God is.
The early Christian fathers said that in the Garden of Eden, Adam knew the existence of God intuitively. He could look at something benign like a leaf falling and see God, the same way one might see gravity. As I said, the five ways are not primarily apologetics; they are primarily to help theists understand the nature of God. They exist to make us all a little more intellectually like Adam in the garden, seeing the world with clarity.