Once there was an astronomer speaking on the subject of earth. He described the ways of gravity and centripetal force and how they keep the planet in position in space. Afterwards a little old lady walked up to him.

“You’ve got it all wrong,” she declared. “The earth does not hang in mid-air. It rests on the back of a turtle.”

The astronomer, learned man that he was, calmly pointed out the problem that then there would be nothing for the turtle to rest on.

“Oh, you just don’t understand,” she replied. “It’s turtles all the way down!”

In the same way, when pressed to give a reason for accepting a certain fact, we offer another one. Our reason for believing this fact is a third, or perhaps a religious speculation. But it can’t go on like this forever; our knowledge can’t be based on turtles ad infinitum.

Thrust your hand into the air in front of your face. Do you know it is there?

Well, of course you do. There is a region in your brain that converts light hitting the retina into electrical impulses that is read as vision. You see your hand in front of your face, and you know it.

That’s very fine. But how do you know your brain works this way? How do you know it works properly at all? Is it okay to accept the science that supports it?

You reason its sound. They are observable facts. There is wide consensus on the issue. It would be madness to purport otherwise.

Now, I respond, we are approaching a problem. How do you know your brain is thinking through this correctly?

Your answer to this question depends on your worldview. Do you believe God exists? Do you believe truth is relative? Do you believe we are here as a result of millions of years of evolution? Do you believe that Jesus Christ is Lord?

Your answers to these questions reveal your worldview, and thus will affect how you answer the question of reasoning properly. And now it’s clear that your knowledge of something as inanely simple as where you hand is at present depends upon your belief in God.

Perhaps you don’t believe in God, or perhaps you don’t believe in the sort of God that is required. And heavens, you know a great deal more than the quack who wrote this, thank you very much.

But that is not the point I am trying to make. Imagine that I do not believe in the existence of that much mythologized and allegedly invisible substance, air. I can’t see it. I can’t feel it. I don’t really know what else I would say on the subject but if I honestly believed it I fancy I could come up with a myriad of reasons.

You, of course, will not accept such nonsense. Without air, breath and speech would be impossible. In fact, if air did not exist, I would not be able to live to present such an argument. I would simply die of asphyxiation and my words would vanish without a squeak as the air upon which my sound waves usually travel through would be gone. The fact that I am able to argue against air’s existence proves that I am very wrong in my beliefs.

Ha! But I will not buy into your nonsense, sir or madam. I don’t believe in air, and I happen to be breathing just now!

It is quite evident that I am arguing a great deal more nonsense than you are at this point; however, you are just as wrong in stating that your own knowledge disproves my argument that knowledge could not exist without (the Christian) God.

Let me return to my turtles. When we replaced the turtles with facts supporting our knowledge of your hand’s position, we paused at the fact of God. It could then reasonably be asked, “So then, how do you know God exists?”

I have just said that knowledge is impossible apart from him. You cannot know that your mind reasons properly unless you believe in a God who created you in His image and said, “Come now, and let us reason together.” (Isa. 1:18) Without Him as your foundation, you can logically prove nothing. You have knowledge, but you deny the one “In whom are hid all the treasures of wisdom and knowledge.” (Col. 2:3)

But isn’t this all circular reasoning? Well yes, in a sense. But remember the turtles. You can’t base your knowledge on “turtles all the way down.” The chain of reasoning has to actually end somewhere. Eventually you will reach a fact that cannot be proved by another one; it must prove itself. We reached the existence of God; can we prove it on anything else?

Not really. You can try to prove Him with logic, but then you must explain how logic got here. You could try to prove Him with science, but then you must answer as to how that is known to exist. Besides, using logic or science to prove God is saying that logic or science is the ultimate starting point, and if I make that the case, my ultimate standard is my own mind.

Even Jesus said that if I don’t believe the Scriptures, I will not believe in its God, even if someone rises from the dead. Indeed, there were those who doubted when they saw Jesus after His resurrection (and an extrabiblical source would be Josephus, who believed He rose again, but remained a Jew). The Bible is to be accepted before all else. Nothing – not even the resurrection of Christ our Lord – can be known apart from it.

And what is the alternative? Autonomy. I become the standard of my own universe. Everything I perceive is known because I perceive it. Solipsism – the belief that the self is the only thing that can be known to exist – is the result.