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Our unit on the philosophy of religion and the existence of god continues with Thomas Aquinas. Today, we consider his first four arguments: the cosmological arguments.


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 Introduction (0:00)

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Hank: Nothing gets people talking like proving the existence of God, just look at the comments on our last video. And that is what Anselm of Canterbury did. He claimed, in the 11th century, to have come up with deductive proof of God's existence, through what we know as the ontological argument. And, if there was such a thing as a social network of medieval Christian philosophers back then, it was positively abuzz with the news. For a long time. 

Because, almost 200 years later, Italian theologian and philosopher Thomas Aquinas encountered Anselm's argument. But, like many others, he just didn't buy it. Aquinas did believe in God. It was just that, as a philosopher, he felt that it was important to have evidence for your beliefs. He knew that if he was going to dismiss Anselm's argument, he'd need to come up with something better.

So, he set out to construct five arguments that would prove God's existence, once and for all. Yeah, five. Apparently, he was concerned one wasn't going to do it, so he figured that, out of five, one was bound to stick. His first four arguments are known together as the cosmological arguments, as they seek to prove God's existence through what he argued were necessary facts about the universe.

So, in keeping with the method that we discussed in our very first episode, we're gonna examine these first four arguments of Thomas Aquinas, and really try to understand them. And then we'll consider their merits, and their weaknesses.

(Crash Course Philosophy Intro)

 Argument from Motion (1:30)

Maybe the most striking thing about the cosmological arguments of Aquinas, at least to modern eyes, is that some of them are firmly based in the natural world. Even though he lived in a pretty unscientific time, Aquinas argued for the existence of God through his understanding of science, and with the help of what he thought was physical evidence. 

For example, the first of his cosmological arguments is known as the Argument from Motion. In it, Aquinas observed that we currently live in a world in which things are moving. And he also observed that movement is caused by movers, things that cause motion. Aquinas was convinced that everything that's been moving must have been set into motion by something else that was moving. By this logic, something must have started the motion in the first place. Otherwise, you'd be stuck in a philosophical quandary known as an infinite regress.

You get an infinite regress when, in a chain of reasoning, the evidence for each point along the chain relies on the existence of something that came before it, which in turn relies on something even further back, and so on, with no starting point. Basically, Aquinas thought the very idea of infinite regress was absurd, logically impossible. Because, it implied that any given series of events began with nothing. Or, more accurately, never really began. Instead, it could have been going on forever. 

In the case of physical motion, Aquinas wanted to trace the cause of the movement he saw in the world all the way back to its beginning. And he figured there must have been a beginning. Otherwise, for him, it would be like watching these blocks fall, and being told that nothing ever pushed over the first block. Instead they had always been falling down forever, backward into eternity. There must have been a time when nothing was in motion, Aquinas thought, and there also must've been a static being that started the motion. And that being, according to Aquinas, is God; the Unmoved Mover.

So, his Argument from Motion ran something like this: 
Objects are in motion. Everything in motion was put into motion by something else. There can't be an infinite regress of movers. So there must be a first mover, itself unmoved, and that is God.

 Argument from Causation (3:20)

Now, the second cosmological argument of Aquinas was a lot like his first one. Here, he proposed the Argument from Causation, and it, too, sets out to avoid of an problem of infinite regress. But instead of it explaining the motion of objects, it set out to explain causes and effects, in general, all over the universe.

The argument went along these lines:
Some things are caused Anything that's caused has to be caused by something else, since nothing causes itself. There can't be an infinite regress of causes. So there must be a first cause, itself uncaused, and that is God. 

Just like with the Argument from Motion, the point here is pretty simple; effects have causes. If you think about how you wound up watching this video, you can trace the line of causation back, from moment to moment. If you think about it long enough, you can probably go pretty far back. but Aquinas said, again; it can't go back forever. There had to be a First Thing that started off the chain of causes and effects. And that Thing is God. 

 Argument from Contingency (4:09)

Argument number three was the Argument from Contingency. And we should step back and get a little background for this one. In philosophy, we often distinguish between necessary beings contingent beings. A contingent being is, simply, put, any being that could have not existed. That includes you. Sure, you do exist, bu you could not have.

If you had never been born, the world would go on. And yes, things would be different, we've all seen It's A Wonderful Life, but the world would go on. Instead, your existence is merely contingent on the existence of other things. In your case, you only exist because a certain sperm met a certain egg and swapped some genetic information. You're basically a fluke.

But what does have to do with God? Well, again, Aquinas believed that there had to be something that prevented an infinite regress of contingency. That would mean that the contingency on which everything existed would just keep going back in time. And we can't have a world where everything is contingent, because then, by definition, it all could easily have never existed. 

So he needed at least one necessary being, a being that has always existed, that always will exist, and that can't not exist, in order to get everything going. And that necessary being is God. 

Aquinas spelled out the reasoning of his Argument form Contingency this way:
There are contingent things. Contingent things can cause other contingent things, but there can't only be contingent things. Because that would mean that there's an infinite regress of contingency, and a possibility that nothing might have existed. An infinite regress is impossible. So there must be at least one necessary thing, and that is God.

Let that marinate in you brain for a minute while unpacking the next argument.

 Argument from Degrees (5:37)

This one is built on the idea that we simply need a measuring stick in order to understand the value of things. Good/bad, big/small, hot/cold, none of these concepts can exist in isolation, If you go out for a walk and you see an animal, and it's like this big, that animal would be on the small side if it turned out to be a dog. But, if it were a rat, that would be huge. How do we know? Because we gauge the size of things in terms of other things. 

The same idea applies to more abstract concepts, like your grades. How do we know that an A is good? Because it's at the top, we know that there are grades lower than an A, but nothing higher. And Aquinas thought that all of our value concepts would just be floating randomly in space if there weren't some anchor, something that defined the value of everything else, by being perfect. And that, again, is God. 

This is how Aquinas developed number four, known as Argument from Degrees:
Properties come in degrees. In order for there to be degrees of perfection, there must be  something perfect against which everything else is measured. God is the pinnacle of perfection. 

 Critical Evaluation (6:33)

OK, we've considered Aquinas; four cosmological arguments. But remember, that's only step one. The next, and equally important step in philosophy, is critical evaluation.

So what do we make of them? As philosophers, if you think an argument is flawed, it's your job to try and figure out why. And by large philosophers, theists and atheists alike, have been relatively unimpressed by these four, having found many problems in them. For one thing, these arguments don't seem to establish the existence of any particular god. Even if the arguments are correct, it doesn't look like Aquinas gets us to the personal, loving God that many people pray to.

Instead, we're left with unmoved mover and uncaused causers who seem to have little in common with the God of Abraham, Isaac, and Jacob, the God who feels emotions, and cares about his creations, and answers prayers. Basically, this objection says that Aquinas' god is so far removed from the God that theists believe in, that it doesn't help anything. 

But maybe you're happy just believing someone's out there. That's fine. But then how about multiple someones? Because, guess what, Aquinas' arguments don't rule out polytheism. There's nothing in any of his arguments to prove that God isn't actually, like, a committee. 

Aquinas' cosmological arguments also don't prove the existence of a sentient God. So, it might be an old guy with a beard. It might be six old guys with beards. But it also might be an egg, or a turtle, or just a big block of stone. These observations have made some philosophers uncomfortable with Aquinas' ultimate conclusion. But there are two objections that are thought by some to be real nails in its coffin. 

The first is simply that Aquinas was wrong in his insistence that there can't be an infinite regress of anything. Aquinas takes it as a given that there had to be a starting point for everything. Whether it's the movement of objects, or causes and effects, or contingent beings being created. But it's unclear that this is true, or why it has to be true. If infinite regress can be possible, then Aquinas' first two arguments fall apart. 

But perhaps the most significant charge made against Aquinas' arguments is that they're self-defeating, that is, they actually prove themselves wrong. For example, if Aquinas is right that everything must have been put in motion by something else, and everything must have a cause other that itself, then it seems that God should be subject to those same stipulations. And if God is somehow exempt from those rules, then why couldn't other things be exempt from them too? If they can exist without God being responsible for them, then we don't need God to establish things in the first place.

 Conclusion (8:43)

All right, I feel like I've given you a lot to think about. So before we close, let's pause and remind ourselves about a couple of things. First, you can accept a conclusion but reject an argument. So you might agree with Aquinas that God exists, but think none of his arguments prove it. Second, if you disagree with an argument, you don't get to just say, yeah, you're wrong. You have to give a counterargument. What did Aquinas get wrong, and how can you do better? Why are your reasons superior to his.

Remember, philosophy is a dialectic. Yes, Aquinas has been dead for centuries. But he started a conversation. And you get to participate in that when you engage in his arguments, and offer your own, either in an effort to help him out, by fixing flaws in his argument while preserving the conclusion, or by refuting the entire project.

This is what it means to do philosophy, to engage with arguments about stuff that matters. And whether or not there's a God seems to matter quite a bit, particularly in the lives of theists. 

 Outro (9:33)

Today we learned about cosmological arguments, and considered four of them. Next time, we'll look at Aquinas' fifth argument, the Teleological Argument. 

This episode of Crash Course Philosophy is made possible by Squarespace. Squarespace is a way to create a website, blog or online store for you and your ideas. Squarespace features a user-friendly interface, custom templates, and 24/7 customer support. Try Squarespace at for a special offer. 

Crash Course Philosophy is produced in association with PBS Digital Studios. You can head over to their channel and check out some amazing shows like PBS Idea Channel, The Chatterbox, and PBS Space Time. This episode of Crash Course was filmed in the Doctor Cheryl C. Kinney Crash Course Studio with the help of all of these awesome people and our equally fantastic graphics team is Thought Cafe.