How do you know that the sun is the center of the solar system and the Earth orbits it?
How do you really know? Because simple observation quite clearly shows the opposite: we’re sitting still and the sun is moving around us in the sky. So how do we know that’s wrong?
We know it because scientists have demonstrated it, sure, but if you couldn’t lean on that, if someone asked you, personally, to prove it from direct observation, (and without relying on any technology that’s left Earth’s atmosphere; that would be cheating,) how would you do it?
It’s a surprisingly difficult question when you really start to look into it. If the Earth is orbiting, it also has to be spinning around in order to produce the day/night cycle we’re familiar with. Occam’s razor suggests that one body in motion in one way (the sun orbiting the Earth) is far simpler than one body in motion in two very different ways at the same time (the Earth orbiting the sun and also spinning.)
Also, if the Earth is spinning at a fixed rate of 1 revolution per day, then things at higher elevations (further from the center of the Earth) are moving around the center faster than things at lower elevations. So if you climb up a tall tower and drop a heavy weight from the top of it, it should have momentum that carries it to the east. Instead, it falls straight down.
Also, if the Earth is moving around through the heavens, then you should see parallax when looking at the stars, with nearer stars seeming to move against the background of more distant stars as the year goes on, but this is not observed.
Therefore, it’s ridiculous to believe in heliocentrism. Right?
Well, that’s what the best scientific minds in the world believed for a long, long time. We know better today, but it took generations of astronomers and physicists centuries to find the proof. It was not until 1791, after the founding of the USA and more than a century after Newton’s theory of Universal Gravitation, that experiments finally provided evidence to disprove the last of these objections. (In the cases of both the dropping weight and the stellar parallax, the answer turned out to be “this really does happen, but it’s a very small effect that’s basically impossible to measure without sophisticated equipment.”)
Up until the late 18th century, it was perfectly rational to believe the sun orbited the Earth and not the other way around. It was not correct, as we now know, but it was very rational.1
But doesn’t “rational” mean “right?”
We often hear critics use the word “irrational” to mean “wrong,” or say that their ideas are right because they’re rational, or that there is no rational basis for believing in things they disagree with.
This is all a bunch of nonsense.
“Rational” means “the conclusions follow logically from the premises.” Nothing more, nothing less. And it very specifically does not mean that the conclusions are right. Here’s a simple example. Let's say you're at a restaurant. You just spent $20 on a meal, and the server asks if you'd like dessert. You'd be able to afford it without any problems down the road if you have over $50 left in your bank account. You had $60 in your account when you went into the restaurant, and you just ate a $20 meal, so reason says no. But if you had had $100 in the account, reason says yes, and so in that case you order the dessert.2
But if you had been mistaken, and thought you had $100 when you really only had $60, reason says yes, and the conclusion will be wrong even though the reasoning is still completely valid. One of the facts that the reasoning is acting upon was incorrect, but the process of reasoning worked exactly as it was meant to.
If the basic facts are correct and the reasoning is correct, then the conclusion will be correct.
Axioms
A very simple fact that is believed to be true without needing proof is known as an axiom. (Or a postulate; the terms are basically synonymous.) For example, when Euclid was writing his foundational treatise on geometry, he set out a few basic postulates, concepts like “you can draw a straight line through any two points” and “all right angles are congruent” that are too simple to prove from simpler principles and appear to be so obvious they don’t require proof.3 Since they cannot be proved by reasoning, axioms are, by definition, not rational. This does not automatically mean that they’re incorrect, though.
All too often, when somebody uses the word “rational” as a criticism, they aren’t talking about rationality at all; they’re really talking about axioms. The most common offender here is when someone takes philosophical materialism as an axiom, the idea that the material world is all that exists. Once you understand that materialism is simply an axiom with no rational proof behind it, you’re able to clearly see all manner of atheistic arguments for the circular reasoning they are: it’s easy to rationally demonstrate that God did not do X if you take as an axiom that God does not exist in the first place!
“The method of 'postulating' what we want has many advantages; they are the same as the advantages of theft over honest toil.” — Bertrand Russel
It gets worse
Scientists and philosophers have been aware of the problems posed by invalid axioms for thousands of years. About 100 years ago, some of the biggest names in mathematics were putting a lot of time and energy into working out a “theory of everything” that could prove all of math from the ground up. This was eventually brought to a screeching halt in 1931 when Kurt Gödel proved that it’s impossible to ever create a system of mathematics that’s both complete and consistent; not only will there always be true statements that cannot be proven, there will also always be ways to create paradoxical (“this sentence is false”) or contradictory (“1 = 0”) mathematical equations in any system complicated enough to be interesting.
Given that all science is ultimately based on the application of mathematics to various data observed in the world around us, these holes mean that the materialist goal of using science to explain away everything around us is rationally, provably doomed from the start.
Does that mean science is doomed or worthless? Obviously not! It would be ridiculous for anyone to make a claim like that on a computer network of all places. We understand full well just how important a role science plays in our lives, and we’re grateful for it. But this is not in any way incompatible with understanding and accepting that it is not, and never can be, absolute.
The Axiom of Faith
If materialism and atheism are axioms, baseline ideas that are not and cannot be proven, what about the inverse? Is the existence of God an axiom too?
Many philosophers have tried to demonstrate otherwise throughout the ages with varying arguments, some stronger than others. One of the earliest was the Cosmological Argument, the idea that because everything we are capable of observing runs on cause and effect, it follows that there must be a cause for the universe as well. It was originally developed by ancient Greek philosophers, then adopted by early Christians, then adopted by Islamic scholars who picked it up from them, and then later came back into fashion in Christian thought. This very adaptability, I think, makes it unpersuasive; the fact that three very different religions with very different ideas of the nature and attributes of their gods could all equally pick it up and say “therefore my idea of divinity did this” makes it kind of a silly argument IMO. (Materialists posit the Big Bang as a first cause, but that has its own problems. One of the most serious is that there are some severe incompatibilities between the state of the modeled universe in the instants after the Big Bang and the reality of the universe we observe today. This is resolved by a bunch of hand-waving, stating that “the laws of physics were different at the very start,” with very little consideration of the deeper implications of that claim. Far from solidifying the problems inherent in materialism, the theory simply moves them around!)
The Teleological Argument (the claim, based on the observation of clear evidences of design in the natural world, that a design implies a designer) suffers from the same problem. It also originated in ancient Greek philosophy before being adopted and adapted by Christian scholars, and it similarly tells us very little about the attributes and character of the designer.
Likewise the Fine-Tuned Universe Argument, while it does an excellent job of demolishing the notion of rational materialism — the only ways to explain it away involve either wild flights of fantasy involving the existence of other universes and crazy string-theory concepts that have never produced a shred of evidence no matter how hard people testing it tried, or positing some alternate notion of an intelligent, purposeful Creator who we’ll most definitely not call God because we’re being Very Scientific And Modern about it — tells us nothing useful about the nature of the Creator besides the fact that it created the universe. It’s essentially equivalent to the Teleological Argument, just hyper-specifically from the perspective of quantum physics.
The theory of the Fine-Tuned Universe does demonstrate that it’s just as reasonable, if not more so, to choose as an axiom the existence of a Creator over the nonexistence of one, but there’s a pretty wide chasm between “the existence of a Creator” and “specifically God as revealed in the Holy Scriptures of Christianity” that none of these arguments even make any attempt at bridging.
This brings us back to a point I’ve made before, that a person can come to a knowledge of the character and attributes of God through the process of experimentation and testing, the same way we gain other forms of knowledge, with the only difference being that you can’t simply say “well this theologian proved it” the way you can say “well this scientist proved that the Earth orbits the Sun.” It can be done, but the work must be done by each person individually.
A belief in God is definitely rational and provable from simpler principles. The axiom in opposition to atheist materialism is not God; it’s faith.
To Be Continued
I was going to write more, going over some specific examples of the difference between rationality and correctness, and how picking bad axioms leads quite rationally to some incredibly crazy conclusions, but this article is getting too long already. Watch for the next one!
A shout-out to The Great Ptolemaic Smackdown for this example. It’s a very interesting series of articles explaining how we got from the heliocentrism of Antiquity to our modern understanding of the solar system, and oh by the way everything you think you know about Galileo is wrong.
Let’s ignore any questions about how reasonable it is to be ordering a $20 meal in the first place with so little money in your bank account. This is just a deliberately simplified example.
There’s also the infamous fifth postulate, which is of great interest to math nerds for, among other things, remaining stubbornly un-provable despite not being simple or obvious. Not going to get into that one here.
Re the Cosmological Argument: The Cosmological Argument is intended to show that God exists, not *which* God exists. Aquinas was very clear on that; his Five Ways are all about showing the existence of a deity; there are other, separate arguments he deploys to show that the Christians have the correct relationship with God.
Excellent compendium of material on the limits of rationality.