Principles of Reasoning

By James M. Rochford

When I was in grade school, I played an older kid in chess during recess. Right before I put him in checkmate, he swapped his king and rook, illegally moving the two pieces out of danger. I objected that this was against the rules, but he said, “This is the way that I play the game.” Every time I went to win the game, my opponent would change the rules, so that he couldn’t lose. The kid was bigger than me, so I let him win. But I never forgot how frustrating it was to play a game with rules that could change on a whim.

In a similar way, we need to agree on ground rules before we examine the evidence for Christianity. Otherwise, like a kangaroo court, we will not be able to reach a responsible verdict on the evidence. However, even as we consider this there will likely be an objection. Whose ground rules should we follow? Let’s consider this common objection.

Isn’t Logic and Reason just a Western way of viewing the world?

Have you ever heard this sort of objection? I have. Some people argue that it is arrogant for someone to create their own ground rules for a discussion on the evidence for Christianity. Why should we appeal to logic, if it was created in the Western world? To understand this objection, let’s consider a fictional dialogue between two people, who are arguing over the importance of logic:

LOGIC: So, what exactly are you saying?

ILLOGIC: I’m saying that Reason and Logic are just a Western way of thinking. They aren’t universally true for everyone.

LOGIC: Really? Do you mean that universally?

ILLOGIC: Yes… I mean no. I’m not sure. Logical thinking comes from the West. The rest of the world shouldn’t have to believe in Logic, if it’s just a Western invention. If you had been born in the East, then you wouldn’t believe in Western logical truths. You’d have a different perspective.

LOGIC: I’d like to hear you say that to a person from the East. They’d laugh in your face. Take the law of non-contradiction, for example. This law holds that two contradictory truths cannot both be true at the same time. Consider if you ask a woman if she is pregnant. She says, “Yes,” but her husband says, “No.” What would you conclude? Could they both be right? No. Either, the woman was lying or the man didn’t know, but she couldn’t be both pregnant and not pregnant at the same time. Is that a Western way of thinking?—or is that just the way that it is?

ILLOGIC: I just don’t agree. Logic doesn’t need to be a part of our thinking.

LOGIC: But, that doesn’t make any sense.

ILLOGIC: Yes, it does.

LOGIC: Wait a minute, do you believe that your view makes sense?

ILLOGIC: Yes, I do.

LOGIC: I don’t understand. If you deny Logic and Reason, then you have to deny that your view can make sense. “Sense” comes from Logic and Reason.

ILLOGIC: I’m not talking to you about this anymore…

LOGIC: Actually, by disagreeing, you’re affirming the law of non-contradiction. You’re saying that you are right, while I am wrong. You’re saying that we cannot both be true at the same time. That’s a very logical way of arguing.

[A long pause…]

LOGIC: Now, I know what you’re doing.

ILLOGIC: What’s that?

LOGIC: You’re just thinking in rational arguments, even if you’re not arguing with them.

ILLOGIC: If you’re right, then I just won’t say anything. If I argue, then I’ll be using the law of non-contradiction. The only thing that’s appropriate is just to remain silent.

LOGIC: That’s a good point. Now, you’re making some sense…

What does this dialogue teach us? It demonstrates the bankruptcy of denying logic and reason. If we deny logic, we find ourselves without a stable foundation in our thinking. Therefore, we need to respect logical truth, as a proper foundation for our worldview. Let’s look at a number of ways to break the rules of logic. These examples are commonly known as informal fallacies. It might be best to try to cover up the answer, figuring them out on your own.

Self-defeating Arguments

This is probably the most common informal fallacy, so we will spend the most amount of time studying it. What are self-defeating statements? These are suicidal arguments which reference and then kill themselves. Consider an example from the movie Office Space. One of the characters asks his supervisors: “What the hell is wrong with you people? Can’t you see that I’m a people person?” Here is a comical example of a self-defeating statement. How could this guy be a people person? He contradicts himself in the same exact sentence! If this statement is true (he is a people person), then he just proved himself wrong with the very same statement. If the statement is false (he is not really a people person), then it is false. Either way, the statement cannot be true.

Consider another example. A cartoon character on a popular TV show said, “Nobody drove in New York… there was too much traffic.” It is easy to spot why this statement is self-defeating, but other statements are not so easy. This exercise will help us identify self-defeating statements:[1]

“No English sentence can be eight words long.”

This sentence is exactly 8 words long. Therefore, the statement itself cannot be true.

“One hundred percent of statistics are false.”

If all statistics are false, then so is this one.

“I do not exist.”

You would have to exist in order to make this statement.

“I don’t have a philosophy on life.”

This is a philosophy on life.

“Universal truth claims do not exist.”

If universal truth claims do not exist, then this truth claim does not exist universally. We might also retort by asking, “Really? Do you mean this universally?—or is that statement true only for you?”

Here’s a Facebook post that I read recently: “Lesson I learned recently: don’t believe anything anyone says. Nobody knows the meaning of the word honesty.”

If everyone is a liar, then so is the speaker. This means that they are also lying about what they are saying.

“I doubt absolutely everything. We can’t know anything for certain.”

If you doubt everything, then you need to doubt your doubt, too. This is otherwise known as philosophical skepticism. A few additional points can be made here, as well.

First, the arguer cannot be completely skeptical about absolutely everything, because this would include skepticism itself. To a skeptic, the person who asserts a worldview needs to defend it. This means that the skeptic needs to defend their worldview—skepticism. In other words, the skeptic needs to offer reasons why we should doubt everything. This is impossible under the skeptical worldview, so it collapses.

Second, if we were truly skeptical about everything, then this would lead to an infinite regression of knowledge. This would be similar to the little kid who asks, “Why?” over and over—much to the chagrin of his Mother and Father. There are certain truths that are self-evident in our world, which terminate the endless stream of Why’s. It appears obvious that we can have some knowledge—even if we cannot have total knowledge. The burden of proof is on the skeptic to answer why we are unable to have knowledge.

Third, implicit in this claim is the belief that we cannot know truth, because we err in our ability to understand truth. And yet, our knowledge of error is not proof for skepticism; it is proof against it. That is to say, the possibility of error presupposes the fact that truth exists. The fact that we can find errors and correct them means that we are supposing that there is an absolute standard of truth to which we are comparing our knowledge claims.

“Logic isn’t a valid way to discover God. It can’t tell us anything about God. God is above our logical understanding.”

This is a logically coherent statement that is arguing against logical coherence. Philosopher Norman Geisler writes, “Look at this carefully. It says that logic doesn’t apply to these issues. But the statement is logical about these issues. It is logical because it claims to be true while its opposite is false. That claim, called the law of noncontradiction, is the basis of all logic. In order to say that logic doesn’t apply to God, you have to apply logic to God in that very statement. So logic is inescapable. You can’t deny logic with your words unless you affirm it with the very same words. It is undeniable. When a truth cannot be denied, it must be true. So this objection is false. Logic can tell us some things about God. For instance, since God is truth, He cannot lie (Heb. 6:18). Logic is a valid tool for discovering truth.”[2]

“I will only believe in what I can see, smell, taste, touch, or hear.”

This criterion for belief invalidates itself. Can you see, smell, taste, touch, or hear this statement? Is this proposition a tangible thing that can be touched and measured and analyzed? No. We can see the words on the page. We can hear them spoken, but we cannot see the proposition itself.

Consider when someone says, “Your words really touched me the other night.” When they say this, they certainly do not mean that the words could be tried for molestation. They do not mean that the words left fingerprints on the person’s body. Rather, they mean that a concept was communicated. When they say that they were touched by the words, they do not mean physically (through the five senses); they mean conceptually (through thoughts and concepts).

Not only is this view self-refuting, but it also eliminates many other properly basic beliefs about the world. Love, justice, meaning, purpose, moral values, numbers, sets, laws of logic, magnetic fields, and historical study all have to be denied if this is true. Think about it! Actually, don’t think about it, because you can’t even believe in your own thoughts in this view!—because thoughts cannot be seen, smelled, tasted, touched, or heard. Atheist philosopher J.L. Mackie agrees with this, when he writes, “This theory of meaning is itself highly implausible. It is well known that the adoption of it would similarly create serious difficulties for the meaning of many ordinary statements, including all those about past, historical, events, or about the minds, thoughts, and feelings of persons other than oneself.”[3]

“All morality is relative to private taste, so you should be more tolerant of other moral views.”

The key here is the phrase “should be.” Why should I be tolerant, if morality is relative to private taste? This statement is a moral imperative, which is expected to be followed. But, how can I have a moral duty to be tolerant if all duties are merely relative?

“Philosophical questions are meaningless or false and only scientific claims are true and rational.”

Look closely. This is not a statement of science. It is a philosophical statement about science. I can’t use instruments and measurements and data to prove that I should use instruments and measurements and data. Put another way, I can’t use the scientific method to prove that we should believe in the scientific method. In addition to this critique, we can see that this view would invalidate many other truths.


Epistemic Limitations to the Scientific Method (MEALS)

Metaphysical Truths

Metaphysical truths cannot be proved through the use of science, but they are still rational beliefs to hold (e.g. there are other minds like my own; the universe was not created 5 minutes ago with an appearance of age; the external world is real).

Ethical and Moral Truths

These are truths that are concerned with our values. There is no way to prove that something is Right or Wrong through the use of science. Morality is not found in a test tube.
Aesthetic Truths

We cannot claim that beauty exists through the scientific method, and yet all rational persons are justified in claiming that something is beautiful (as every teenage boy will tell you as they go through puberty).

Logical and Mathematical Truths

Science presupposes Logic and Math. If someone tried to prove these through the scientific method, they would be arguing in a circle.
Scientific Truths

Remarkably, it is self-defeating to use science to prove science. The scientific method is a philosophical and rational principle used to produce science, but it is not a product of science.


Genetic fallacy

This style of argument deals with the origin of the belief that it is being argued. The fallacy is committed when the debater attempts to show where the belief originated, in order to disprove it. If we can show the motive or reason for believing something, then we have proved that it is fundamentally false. But this does not disprove the argument itself, it merely shows where it came from. Let’s critique a few examples of this.

“If you had grown up in a racist home, then you’d probably be a racist.”

This might be true, but it doesn’t prove that racism is good or bad. It just proves how you became a racist.

“If you had grown up in an atheist home, then you’d probably be an atheist.”

This is probably true, but it doesn’t prove that atheism is true or false. It just proves how you came to believe in it.

“You are a Christian and not a Buddhist because you were raised in a Christian country and your parents taught you to be a Christian. Therefore, there is no good reason to prefer Christianity to Buddhism.”

This commits the genetic fallacy, because it merely shows how a person became a Christian. It doesn’t disprove Christianity. It may be true that I learned about Christianity through upbringing or culture, but this doesn’t prove it false. It merely shows how I learned of it.

This style of argument can be turned around on a dime. You might ask this arguer, “Do you believe that the Earth is round? You do? Well, you only believe that because you learned it in a fourth grade science class.” They would respond that such an argument is fallacious, but then we could explain that their argument is equally false. Just because I came to know about the truth of Christ from culture or upbringing, this does not prove or disprove the truth-claims of Christianity. The way in which I learned of this truth is erroneous. The truth or falsity of a claim is what matters.

“You are a Christian because you hit a hard time in your life, and you needed something to cling to.”

This statement is quite possibly true for many Christians, but does it prove Christianity false? Perhaps I did need something to cling to, but this does not disprove Christianity. Perhaps, I was clinging to Someone who was actually there. This doesn’t disprove anything; it only shows how I came to believe this.

Straw man argument

This invalid type of argumentation is committed when an arguer distorts an opponent’s position for the purpose of making it easier to destroy, refutes the distorted position, and then concludes that his opponent’s actual view is thereby defeated. They misrepresent the other person’s position, and they show the misrepresented position to be false. But, their actual position may go untouched by the arguer:

“Steve believes that we should give more money to the poor in Africa. But, I just can’t stand behind an idea that is going to take money out of our children’s pockets and ruin our economy in America. I’m telling you… Don’t buy into Steve’s charity garbage. It’s going to rob your own kid’s future!”

Steve doesn’t believe that we should steal from kids or the economy. He believes that we should give money to the poor. Steve’s view isn’t being accurately represented.

“All Christians think that the world began 6,000 years ago, they believe that Noah’s ark held every species that we see today, and they don’t believe that any evolutionary change has occurred. None of this makes any sense, so Christianity should be rejected.”

This isn’t what Christians believe (nor what the Bible teaches!). It’s all lumped together and then defeated.

“I could never believe in Christianity, because it teaches that God sends non-Christian babies to hell, burning in an eternity of fire and brimstone. A good and loving God would never allow such a thing to happen.”

Before we respond to this question, we need to ask if this is an accurate portrayal of the biblical view of hell. This is a sensational and inaccurate view of hell. They paint an inaccurate picture of hell, and then, they defeat it.

“Christians believe in everything from witch hunts to snake handling to the sale of indulgences. These are all absurd. Therefore, there is no good reason to support the Christian faith.”

Some Christians have extremist beliefs, but this does not defeat a core proposition like “God loves the world” or “Jesus died for sins.”

False Dilemma

This is also known as a false dichotomy. This happens when we reduce a problem to only two possible solutions, even though there are more than just two available:

“Either you can walk, or you can chew bubble gum. But, you can’t walk and chew bubble gum at the same time.”

What? I do that every day! Why does it have to be one or the other?

“Faith is either based on reason, or it is based on experiencing God in our life.”

Why must it be one or the other? Why can’t we have both?

“Either we get truth from the Bible, or we get it from Science.”

All truth is God’s truth, whether it is revealed in his word or in his world.

“We can either have true and total knowledge of God and the universe, or we are lost in a sea of relativity—unable to know anything certainly.”

Both of these alternatives are false, so we need to split the horns of the dilemma. We might ask, “Why can’t we have true knowledge, even if it isn’t total knowledge of God?”

This is the claim of the Bible. The Bible teaches that we never have exhaustive knowledge of God, but we can have accurate knowledge. Paul writes, “[I want you] to know the love of Christ which surpasses knowledge” (Eph. 3:19), but he also writes, “[You should] attain to all the wealth that comes from the full assurance of understanding, resulting in a true knowledge of God” (Col. 2:2). While the love of Christ “surpasses knowledge” that is not to say that I am unable to claim the proposition “God is love” (1 Jn. 4:8). The Bible is by no means an exhaustive recording of the infinite-personal God, but then, who could read it if it was (Jn. 20:30-31; 21:25)?

In fact, this claim wouldn’t work in any field of study. While Stephen Hawking doesn’t have total knowledge of physics, he still has true knowledge of physics. Put another way, a car mechanic might not know everything about cars, but he still knows something about cars.

Leibniz’ Law of the Indiscernability of Identicals

For any x and any y, if x=y, then whatever is true of x is true of y and vice versa.

How do we prove that the law of identity is false in certain assertions? We have to show that something is true of one is not true of the other.

Modus Ponens

“The method of putting.”

If P, then Q


Therefore, Q

If God doesn’t exist, then there is no mind.

God doesn’t exist.

Therefore, there is no mind.

Modus Tolens

“The method of taking.”

If P, then Q

Not Q

Not P

If God doesn’t exist, then there is no mind.

There is a mind.

Therefore, there is a God.

[1] Much of this study was based off of Moreland, James Porter, and Dallas Willard. Love Your God with All Your Mind: the Role of Reason in the Life of the Soul. Colorado Springs, CO: NavPress, 1997. 119-120.

Geisler, Norman L., and Ronald M. Brooks. “Chapter Six: Informal Fallacies.” Come, Let Us Reason: an Introduction to Logical Thinking. Grand Rapids, MI: Baker Book House, 1990.

[2] Geisler, Norman L., and Ronald M. Brooks. “Chapter One: The Need to Answer Every Man.” When Skeptics Ask. Wheaton, IL: Victor, 1990.

[3] Mackie, J. L. The Miracle of Theism: Arguments for and against the Existence of God. Oxford [Oxfordshire: Clarendon, 1982. 2.