One of the funniest, craziest, and most iconoclastic philosophers of
ancient Greece was a guy named Diogenes the Cynic. Like Plato,
Diogenes was a student of Socrates. But they could not have been more different.
Where Plato liked to build up, Diogenes liked to tear down. Where Plato’s philosophy was mostly
constructive, Diogenes’s philosophy was mostly destructive. Where Plato
would put forward hypotheses and see where those hypotheses led,
Diogenes would challenge Plato’s hypotheses and call into question his principles.
One story illustrates this difference perfectly: when Diogenes heard that Plato and his students
at the Academy were defining “human being” as “a featherless biped,” he caught a chicken,
plucked its feathers on his way to the Academy, and then threw the now-featherless
chicken through the Academy's gate, loudly declaring, “Here, O Plato,
is your human being!” It’s no wonder Plato described Diogenes as “Socrates gone mad.”
But we need people like Diogenes. We need philosophers who will challenge us,
criticize us, and call us out when our arguments move too quickly or our starting-points aren’t
quite right. It keeps us honest. And that’s as true for St. Thomas as it was for Plato.
When we entertain objections and take seriously various critiques of his thought, we are doing
precisely what Aquinas himself did and would have done—and precisely what he would want us to do.
With that in mind, I’d like to subject the first way to a bit of critical reflection.
Recall that the argument of the first way goes like this: something changes; but everything
that changes is changed by something else; so something is changed by something else;
but if something is changed by something else, then there must be an unchanged cause of change—an
unmoved mover; so there must be an unmoved mover; and an unmoved mover is what we call ‘a god’;
so there must be something that we call a god.
The weakest link in this chain of reasoning is the premise that says “if something
is changed by something else, then there must be an unchanged cause of change—i.e.,
an unmoved mover.” Why should we think that? What’s the connection between
something being changed by something else and the existence of an unchanged cause of change?
St. Thomas thinks he can prove the connection by using a style of argumentation called reductio
ad absurdum. It works by assuming the thing you want to disprove,
and then showing that something insane follows from that assumption.
So, suppose we’re arguing about whether a hotdog is a sandwich.
You say it is, because a sandwich is just food wedged inside of other food,
and a hotdog is a piece of . . . meat . . . wedged inside a bun.
I reply with a reductio ad absurdum argument: “Let’s assume you’re right,” I say “and a
sandwich is just food wedged inside of other food. Well, if that were true, then ice cream wedged
between two waffles would be a sandwich. But that’s crazy, so you must be wrong.”
Aquinas’s reductio works the same way: “let’s assume,” he says “that something
is changed by something else and there’s not an unmoved mover. Well, if that were true,
then every mover would be a moved mover—every cause of change would itself be changed—and so
there would be an infinite number of movers. But that’s crazy, so you must be wrong.”
That’s a good reply, but we shouldn’t give up on our work of self-criticism quite yet.
We can still ask why we should think it’s crazy to have an infinite number of movers.
After all, there’s nothing wrong with saying that are an infinite number of even integers,
or that the ratio one-third has an infinite number of decimals,
or even that the days and years of the world could go on to infinity.
In fact, Aquinas thought it’s philosophically possible for
the world to have been created without either a temporal beginning
or a temporal end (even though we know by revelation that it was, in fact, created in time).
But if all of that is right,
then there should be no problem with an infinite series of moved movers:
just imagine an infinite series of torches, where one torch lights another, which lights another,
which lights another, going on forever in both directions. Is that really so crazy?
It’s not. And St. Thomas would agree. Because the infinite series of moved
movers that Aquinas has in mind in the first way aren’t like torches,
or days, or numbers. What he has in mind are infinite series of secondary moved movers.
To see what he means by this, what he means by secondary, imagine there’s a booth inside a room.
The booth is made entirely of glass and has no
interior lighting. You’re in the booth, but you can see just fine.
The only explanation for your ability to see is that the room outside the booth is lit.
But what happens if the room outside the booth is also made entirely of glass and
has no interior lighting? In this case, the outer room will no longer explain
your ability to see inside the booth. That’s because, before it can explain
the light of the booth, it first has to have an explanation for its own light.
Only after we have an explanation for the light of the room (for example,
the shining of the sun outside) will the room be able to explain the light of the booth.
This is what Aquinas means by a secondary moved mover—it is something that can change
something else only on the condition that its own change has been fully explained.
So, could there be an infinite series of secondary moved movers? Could we have an
infinite number of nested glass rooms all of which lack interior lighting,
and yet still be able to see inside the booth? No.
Because an infinite series is always incomplete, and a secondary mover can only cause a change
in something else when its own change has a complete explanation. Thus, if something is
changed by a secondary moved mover, then there must be a primary unmoved mover—otherwise,
the secondary mover wouldn’t be a mover at all.
One final skeptical push: Does Aquinas’s answer beg the question? Has he given us any reason
to think that are such secondary moved movers? I think the answer is “no” to both these questions.
No, Aquinas’s answer doesn’t beg the question. And no, he hasn’t attempted to prove that
there are such secondary moved movers. But that’s because he doesn’t think he has to.
Remember that this is the first way—the more obvious, the more evident, the more palpable
way. Aquinas thinks that our senses can deliver premises that reason can’t prove. Things change.
And they don’t just change in the torch-lighting-torch or day-following-day way.
They also change in the room-lighting-booth way.
Secondary movers are part of our experience. And since there cannot be an infinite series
of secondary movers, it follows that there must be a first, unmoved mover—i.e., a god.
There is almost certainly more that could be said in objection to—and
defense of—Aquinas’s first way. Who knows what Diogenes would say to it! But for now,
it's enough to see that critical reflection is not always purely
destructive. It can also reveal a depth and a subtly that makes the argument stronger.
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