A generous friend of mine allowed me to post his notes on Greg Bahnsen’s lecture series, A Biblical Introduction to Apologetics.
Brain tissue, in the nature of the case, is something material. What controls what physical things do? Scientists will tell you that the laws of nature (the laws of biology, the laws of physics) control what happens to physical things. But if all of our thought processes are controlled simply by brain tissue, which itself operates according to the laws of physics and biology, then there is in fact no freedom of thought. What we think is controlled by the laws of physics and biology, and that’s all there is to it. There’s a certain kind of stimulus that comes into the system, and that stimulus, according to the laws of physics and biology, controls what happens in our brains, and our brains then give us the thoughts that we have. What’s the point of this? The unbeliever has just undercut any possibility for intellectual exchange by saying that. Let’s consider the implications of having brains that are controlled by the laws of biology and physics, and not under any voluntary control, either in terms of what we choose to think about, how we think about it, or even choosing between options. If we don’t have that kind of mental freedom to think through an issue, weigh the evidence, and choose an option, then the unbeliever has no reason to be proud of anything he thinks of. On the unbeliever’s worldview, he can’t help but think what he thinks. When he says naturalism is true (i.e., that there is no such thing as the supernatural; the only thing that’s real is the material world operating by the laws of physics and biology) I have no reason to respect his opinion because, on his worldview, that’s just the laws of biology and physics leading him to say that sort of thing. He couldn’t help doing that. It’s not like he could consider all the different options, weigh the evidence in favor of them, and make an intelligent choice, because there’s no choice at all. He’s just saying that because he has to say it. When you say this to the unbeliever, he’ll disagree and insist….
Atheist: “No, I’ve thought through the worldviews and weighed the evidence, and have come to a rational conclusion.”
You want to tell him….
Christian: “No, it couldn’t have happened that way on your view of the world. On your view of the world certain stimuli came into your ears and eyes, and your brain tissue did certain kinds of things, there were certain electrical stimuli that ran through your nervous system, you had an idea, and you just uttered this idea. Your vocal cords responded to the stimulus and you said naturalism is true. That is no more intelligent a process than the growth of weeds. Weeds grow according to the laws of biology and physics too, and your thoughts and weeds are on the same level given your worldview. Now Idon’t think they are. In fact I think your claim that naturalism is true is something that has such eternal significance that you will go to hell for it if you carry that claim unto death. So I honor the freedom of thought that’s there, and I think you’re wrong in what you’ve said. But put that aside a moment. Maybe that’s just my “Christian prejudice”. All I want to tell you right now is that, on your worldview, you can’t encourage me to believe anything because I don’t have the choice to believe anything anymore than you do. My brain operates according to the laws of physics and biology, and if it only operates according to those, then there’s no choice in the matter. I think the things that I think because I have to think them, and I can’t make an intelligent choice.” So if naturalism is true, then the unbeliever has no reason to think that naturalism is true, because he doesn’t have a brain that operates with the freedom of intellect, but only a brain that operates according to natural laws. The unbeliever has undercut himself. He’s advancing a point of view as being true, but in terms of his worldview, there’s no truth about it. There’s just inevitability. And if he has no freedom of thought, and I have no freedom of thought, then why should we carry on the debate? We can begin to see a refrain that can be used over and over again….”