Everyone agrees that Aquinas’s famous “five ways” are supposed to be proofs of God’s existence. But
what does it take to prove something? Is it enough just to persuade or convince
the person you’re talking to? Or does proof require something more?
For St. Thomas, the answer is clear: proof requires something more.
You can persuade or convince someone that what’s false is true and what’s right is wrong. But
the mere fact that you can convince someone that something is true doesn’t make it true.
Just think of the serpent in the garden of Eden. The mere fact that the devil convinced Eve that
it was okay to eat the apple, didn’t make it okay to eat the apple. And that means he didn’t prove
that it was okay to eat the apple. Because if you’re gonna prove something, it has to be true.
So, is that the answer? Is proof just persuasion plus truth, or does it require something more?
Once again, for St. Thomas the answer is clear: proof requires something more.
Imagine you’re leaving the office when a coworker tells you not to forget your
umbrella. “Is it raining?” you ask him. “Well,” he says, “I checked the weather before going to bed
last night, and it said there would be a 100% chance of rain at 5:00 pm today.” Convinced,
you grab your umbrella, leave the building, and discover that it is, in fact, raining.
Clearly, your coworker has persuaded you of something true.
But did he prove it? No. At least, not according to Aquinas. Your coworker may
have given you good reason to believe that it was raining, but he didn’t prove it.
The reason is because there’s no necessary connection between the weather report saying that
it will rain at 5:00 pm and it actually raining at 5:00 pm. The weather report could have been wrong.
But for St. Thomas, if you’re really going to prove something,
then you can’t leave any room for error.
That matters for how we read and think about the five ways. Because these five arguments
aren’t just intended to persuade us that there’s a god. They’re not just supposed to convince us
of that truth. They’re actually supposed to prove it. And that means that the five ways
will only work as Aquinas intended them to work if they don’t leave any room for error.
We have to know with certainty that the premises are true,
and there has to be a necessary connection between the premises and the conclusion;
it can’t be like the weather report and the rain.
That’s a high bar—and if we want to be fair and honest readers of the five ways,
it’s important for us not to move that bar any lower than Aquinas himself actually set it.
But it’s equally important for us not to raise the bar any higher than Aquinas himself actually
set it. I say that because one of the most common criticisms aimed at the five ways
is that they’re too weak—that they don’t really prove the existence of God—because
they don’t really prove the existence of an all-powerful, all-knowing, all-good,
all-loving, all-merciful being. But that’s not a fair objection.
We should evaluate arguments on the basis of what they actually set out to prove,
not on the basis of what we wish they set out to prove. And Aquinas’s five
ways aren’t intended to prove the existence of an all-powerful, all-knowing, all-good,
all-loving, all-merciful being—at least not directly.
Of course, Aquinas thinks that God is all-powerful, all-knowing, all-good,
all-loving, and all-merciful. And he does think we can prove each one of those things.
But he doesn’t think the five ways are those proofs. All he intends the five ways to prove
is that there such a thing as ‘a god’—according to five very precise ideas of what ‘a god’ might be.
So, if we’re going to be fair and honest interpreters of Aquinas’s five ways,
we have to make sure we’re setting the bar neither too high nor too low: on the one hand,
we have to recognize that the five ways really are intended to be proofs in Aquinas’s strong sense of
the word ‘proof’; on the other hand, we have to recognize what they’re intended to be proofs of.
And that means we should avoid imposing our own ideas and
expectations on Aquinas. We should begin by looking at what he thinks ‘a god’ is,
and ask whether his argument fail or succeed in proving the existence of that.
Viewed from this perspective, the five ways all have the same basic
structure: “__________ (blank) is what we call ‘a god’; but some being is a __________ (blank);
therefore, some being is what we call ‘a god’.”
The first premise clarifies what we mean by the word ‘god’. The second
affirms that something matches that meaning. And the conclusion
asserts what we were trying to prove: that something is a god.
This is actually just a particular application of Aquinas’s general theory of how we prove the
existence of anything: we start with the meaning of a word; we show that
some being matches that meaning; and then we conclude that the word refers to some being.
So, let’s consider an example taken from the natural sciences. Do aas exist? Yes,
and here’s a proof: (1) a volcanic rock consisting of angular blocks of lava with
a very rough surface is what we call an ‘aa’; (2) but there are volcanic rocks
consisting of angular blocks of lava with a very rough surface; therefore, there are aas.
As this example should make clear, if you want to dispute the existence of aas, you should focus
your objection on the second premise, rather than the first. If you refuse to accept the definition
of ‘aa’, then you’re not really engaging with the argument. The genuine debate is over whether there
are volcanic rocks consisting of angular blocks of lava with a very rough surface.
And the same goes for the five ways.
Each one of the five ways begins with a plausible definition of the word ‘god’,
affirms that something satisfies that definition, and then concludes that there is a god.
Of course, someone can refuse to accept the definition of ‘god’ used in one of the five ways,
but then that person wouldn’t really be engaging with Aquinas’s argument.
The genuine debate is over the second premise—whether there actually is anything
that satisfies the definition in question. And, as it turns out, that second premise
is exactly what Aquinas spends most of his time defending in each one of the five ways.
In the rest of this series, we’ll be looking more closely at the different
definitions of ‘god’ that Aquinas uses in each one of the five ways,
and the details of his argument that something satisfies those definitions.
As you think about those arguments, I encourage you to keep two simple questions in mind:
first, has he proved it? And second, what, exactly, is he trying to prove?
And if you want help in thinking those questions through, please
take a look at the rest of the videos in this series on Aquinas’s 5 Ways.
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