How to Use a Reductio Ad Absurdum (Christian Apologetics Guide)

One of our ThinkSquad members asked about performing a reductio ad absurdum. So let’s dive into it and learn about how to reduce non-Christian arguments to absurdity.

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What Is the Reductio Ad Absurdum Technique?

We are talking about how to reduce non-Christian arguments to absurdity, but our project is bigger than that. We can show that the whole non-Christian worldview (not just the argument) is absurd. So we need to talk about what it means to have an absurd worldview. 

To do that, imagine the following scenario.
Imagine you downloaded a new GPS (maps) app. Say you wanted to get to Downtown Chicago, so you pulled up the app and tapped in the coordinates: State St. and Madison St., in the heart of the City. Now, imagine that the app's turn-by-turn directions started out well, but then instead of guiding you to the Windy City it took you to a dead-end street in Aurora, Illinois. Then, when you tried again, it took you to the middle of a corn field in Indiana. After two attempts, what would you conclude? Would you say, "Ah, I guess there's no way to get to Chicago after all?" Or would you say, "Maybe I need a new GPS app?"

Now, here's the point. Your worldview is kind of like a GPS app. It should take you from your starting presuppositions—those basic beliefs that you begin with—all the way to your "destination." In this case your destination is something that is true about the world, or a belief that makes sense of the world.

For example, let's take the belief that "Murder is wrong." We'll make that the "destination" where we want to arrive. A good worldview is going to take you all the way from your starting presuppositions to that belief, "Murder is wrong," without any contradictions.

What Is An Example of a Reductio Ad Absurdum?

A reductio ad absurdum reveals the contradiction in an argument or worldview, in order to show that it is absurd. 

A contradiction is, "a difference or disagreement between two things which means that both cannot be true” ("Contradiction," Merriam-Webster, accessed 5 November, 2021, https://www.merriam-webster.com/dictionary/contradiction).

Contradictions occur when you have two conflicting statements that can't both be true in the same way and at the same time. So to stick with our example, it would be a contradiction if you wanted to get to "Murder is evil," but one of the basic beliefs of your worldview was "Nothing is good or evil." This would be a contradiction, because it involves two statements that can't both be true in the same sense, at the same time:

"Nothing is evil."

"Something (murder) is evil."

If your worldview leads you to a contradiction, then it's an absurd worldview. It's like a GPS that leads you to a dead end.

Is Reductio Ad Absurdum a Good Argument?

It is important to expose the absurdity of a worldview. As Christians, our apologetics is to be motivated by a desire to set Christ the Lord apart as holy.

“but sanctify Christ as Lord in your hearts, always being ready to make [b]a defense to everyone who asks you to give an account for the hope that is in you, yet with gentleness and fear” (1 Pe 3:15). 

Jesus is the truth, and for that reason Christians should be lovers of truth and haters of falsehood. So we should want to fight falsehood even for that reason. 

Moreover, pointing out the absurdity of a false worldview is also an act of love toward our neighbor.

This is because one's worldview provides the answers to life's most important questions. If your worldview is faulty, then you're stuck with wrong answers to those questions—about God, human nature, and the meaning of life.

And like a faulty GPS app leads you to a dead end, a faulty worldview leads people to Hell—the ultimate "dead end." This is because it doesn't tell you the truth about God's holiness, your sin, and how God forgives sin through Jesus Christ.

Having the correct worldview is a matter of eternal life and death. So one of the most loving things a Christian can do for a non-Christian is to show him that his worldview is absurd. We must not do this to make him feel bad, but to encourage him to give up absurdity which leads to death, and turn to the Lord Jesus, who is "the way, the truth and the life" (John 14:6). You want the person to believe the Christian message.

There is another Bible passage that speaks to this truth.

“Do not answer a fool according to his folly, lest you yourself also be like him. Answer a fool according to his folly, lest he be wise in his own eyes” (Pr 26:4–5).

Unbiblical worldviews contradict themselves and are foolish. However, as long as a person doesn't see that, he will remain "wise in his own eyes." "Answering a fool according to his foolishness," and by that I mean showing him the absurdity of his worldview, may help him realize the folly of his position and bring him closer to believing in the truth of the Gospel.

Of course, the absurdity of your non-Christian friend's worldview might not be obvious at first. Because of this, and because you love this person and want to lead him to Christ, you may need to do some work to uncover the absurdity—to "reduce" his position to absurdity. 

Okay, so you have now seen what it means to have an "absurd" worldview—it's when your worldview leads you to a contradiction. You've also seen why it's important to point out the absurdity in someone's worldview—it's because you want them to give it up and embrace the Christian message. In terms of evangelism, a reductio ad absurdum is indeed a good argument.

How is Reductio Ad Absurdum Used?

There are three steps to this. 

Step 1: Clarify your discussion partner's position. 

In order to respond accurately, you need an accurate understanding of what he means. Consider asking the following questions.

1. What do you mean by that? 

2. Is that absolutely true?

3. By what standard? 

4. How do you know that?

5. So what?

Step 2: Identify where your discussion may have a contradiction in his worldview. 

Find the conflict between the "destination" and his "starting point" (basic presuppositions).

For example, he may say that murder is absolutely immoral, but also believe that there is no absolute morality. Ask questions to reveal this. 

One more example: your friend might say that she believes in science, but that the universe is governed by random chance.

Note: sometimes two beliefs might not seem contradictory at first, but together they produce a contradiction. For example, "I believe in science" and "the world is governed by chance" don't directly contradict. But they produce a contradiction in this way: 

• Science relies on consistency and reliability in the universe—we call this "uniformity in nature."

• A universe governed by random chance would not be consistent and reliable.

• So the person believes that the universe is consistent and reliable, and that it is not consistent and reliable. This is a contradiction, see?

Step 3: Push the unbeliever toward the contradiction. 

This might seem counter-intuitive. After all, don't we want the unbeliever to abandon his contradictory, unbiblical position? Yes we do, and that is exactly why we must do this.

Before your conversation, he may have been complacent in his worldview. He was holding contradictions, but he didn't know it, so he didn't feel bad about it. Your goal is to show him that his worldview is actually absurd, in order to make him feel restless and dissatisfied with holding it! 

This is the reductio ad absurdum. 

You reduce the contradictory position to absurdity by uncovering its internal contradictions, between its presuppositions and its conclusions. And because it is contradictory, it must be false.

You perform a reductio ad absurdum to make him deal with the absurdity of his worldview. And like a faulty GPS app, it should be abandoned. This is what you want your discussion partner to realize. 

Reductio Ad Absurdum Practice

Can you identify the contradictions in the following sets of statements?

Set 1:

• “Morality is subjective.”

• “Hate is objectively immoral.”
  
  This produces a contradiction because the hatred being objectively immoral means it is not subjectively immoral, which contradicts the belief that morality and moral standards are subjective.

Set 2:

• “The world is ruled by random chance.”

• “Science is a reliable way of discovering truth about the world.”
  
  This is a contradiction because science requires the world to behave in a non-random way, but a world ruled by random chance wouldn't do that, making science unreliable.

Set 3:

• “All that exists is made of matter.”

• “Laws of logic (which are immaterial) tell us what's true or false.”

This is a contradiction because if laws of logic are real, and they are not made of matter, then not all that exists is made of matter.

Set 4:

• “Humans are the product of unguided evolution by natural selection over millions of years.”

• “Your life has a meaning, purpose and value.”
  
  This produces a contradiction because neither an unguided process, nor what it produces, can assign meaning, purpose and value to anything. It would be like asking for the meaning, value and purpose of a jug of milk spilled onto the kitchen floor (I believe this example comes from Greg Bahnsen). "Unguided process" negates meaning, purpose and value.

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This is Question #6 in our current project of providing 100 answers to 100 questions. If you found it helpful, please join the cause. Sponsor a question and support the work of The Think Institute now. Learn more here.