Why can we trust reason?

Jordan's last question turns the discussion back on something we have used in every lesson so far: reason itself. If explaining where a belief came from is not the same as showing that it is true, what makes our reasoning trustworthy?

There is a difference between what causes a thought and what makes the thought reasonable. Naturalism has to explain why reasons can really support conclusions, while theism begins with a rational source for both the world and our minds.

Every argument in this course depends on our ability to follow reasons and evidence. So before Step 1 ends, it makes sense to ask why we should expect our minds to be capable of knowing truth in the first place.

What caused a thought is not the same as what makes it reasonable

Suppose I ask why you think a bridge is unsafe. You could say, “Because neurons fired in my brain.” That tells me something about what happened physically. It still does not tell me whether you have a good reason to believe the bridge is unsafe. If you say, “Because I saw a large crack in a support beam,” now you have given me a reason.

What causes a thought and what makes it reasonable are different questions. When we reason, we do not just notice that one thought came after another. We believe a conclusion because the evidence actually supports it.

Consider two people who both believe the bridge is unsafe. The first person believes it because he saw the cracked support. The second believes it because someone gave him a drug that makes him terrified of bridges. Both beliefs involve activity in a brain. Both have physical causes. But only one person has evidence that the bridge is actually unsafe.

Knowing what happened in someone's brain still doesn't tell us whether that person has good evidence. A brain scan could tell us what parts of someone's brain were active while he worked through an argument. It could not tell us whether the argument was good. To answer that, we still have to ask whether the evidence supports the conclusion, whether the reasoning follows, and whether a mistake was made.

Now put that inside naturalism. Naturalism says that nature is all there is and that human minds ultimately come from natural physical processes. That does not mean a naturalist cannot reason. Of course naturalists reason. The issue is whether physical causes alone are enough to explain the reasoning they are doing.

A naturalist does not normally say, “I believe naturalism because my brain happened to produce that belief.” He gives reasons. He points to evidence. He expects those reasons to count in favor of his conclusion. So naturalism has to explain more than why one brain state caused another. It also has to explain why one belief can really give us a good reason for another. C. S. Lewis and Victor Reppert have pressed versions of this problem.

Plantinga raises a related question. Natural selection favors traits that help organisms survive and reproduce. True beliefs often help with that, so survival and truth can overlap. But they are not exactly the same thing. Plantinga argues that if naturalism and evolution give us reason to doubt whether our minds are generally reliable, that doubt would also reach our belief in naturalism. Plantinga approaches the issue differently, focusing on whether our minds are generally reliable.

Christianity gives a direct answer. Reality ultimately comes from a rational God. He made an ordered world and creatures capable of knowing it. On that view, it is not surprising that logic applies, that evidence can point toward truth, or that human minds can understand the world around them. We can reason badly, but there is a reason to expect our minds to be capable of truth at all.

None of this means brains do not matter. They do. It is that describing what happens in the brain does not by itself tell us whether the reasoning is good. Theism gives us a rational source for both the world we are trying to understand and the minds doing the understanding.

We can now look at Step 1 as a whole. Contingency points toward a necessary foundation. Kalam argues for a cause beyond the physical universe if it began. Design examines whether intelligence explains the order of nature, and morality and reason raise questions about that source's character. We are not proposing a different god for each problem. The case is that one self-existent, rational Creator explains these features together. That is a further inference worth defending. Each argument still needs to stand on its evidence. Taken together, though, they can strengthen the case for one Creator.

Bottom line: A physical cause can explain why a thought happened without telling us whether the thought is reasonable. Rational thought depends on reasons actually supporting conclusions. A rational Creator gives a strong explanation for why an intelligible world and minds capable of knowing it fit together.

This is not an argument against neuroscience, and it does not claim that every human thought is reliable. Brains are involved in reasoning, and people make mistakes. The question is whether a physical description alone explains rational inference and our ability to know truth.