The reductio ad absurdum is perhaps one of the most useful and important philosophical arguments.
The Latin name given to the argument seeks to accurately describe it—that is, it means to “reduce to absurdity.” The point is easy to grasp, I think.
An argument that is self-refuting is one that can be reduced to absurdity. This argument is a favorite among presuppositional apologists because the PA’s point is that non-Christian worldviews all reduce to absurdity. Although it’s tempting, I will refrain from spending too much time making that association here, but instead make a practical application to that end a bit later.
So what’s an example of an argument that reduces to absurdity? Consider the following statement: All knowledge is derived from the use of the five senses.
But there’s a problem. The statement makes a knowledge claim which was not derived from the five senses! The claim is a philosophical one that reduces to absurdity because it cannot sustain its own burden.
Since one could not know via the five senses that all knowledge derives from them, this claim is self-refuting and, therefore, absurd.
Many don’t realize how this thinking has crept into everyday use. Consider the wayward child who wishes to follow his friends in a risky endeavor, despite knowing the potential consequences: “But everybody will be there!” he protests.
Mom and dad, in their wisdom, reply to the child: “Oh yeah, well if everybody jumped off a bridge, would you do that too?” The point is that if you follow the child’s thinking to its logical conclusion, it creates an absurd situation.
We see this kind of thing in popular New Atheist arguments. “Only the hard sciences provide truth.” Really? Is it true that only the hard sciences provide truth? If so, then the claim is false, because we did not apprehend that truth by using the hard sciences.
The most common and potentially most recognizable is the post-modernists’ claim that there is no truth. But if it’s true that there is no truth, then it’s also true that there is truth—a glaring contradiction.
As you see, this can be a very powerful tactic, because a surprising number of arguments which seek to set themselves up against the knowledge of God fall into this trap.
Speaking of tactics…
Tactics
One of my favorite authors, Greg Koukl, calls this the “Taking the Roof Off” tactic in his book, Tactics.
He provides a helpful illustration to set up the study:
If you were visiting Los Angeles and wanted to go to Santa Barbara up the coast, someone might draw a map to guide you to your destination. If, however, you followed the instructions very carefully and took the highway they suggested but found yourself in Riverside, on your way to the desert, you would know something was wrong with the route you were given. In a similar fashion, worldviews are like maps. They are someone’s idea of what the world is like. The individual ideas making up a worldview are like highways leading to different destinations. If you use the map but arrive at a strange destination, either part of the map is inaccurate (the part about the highway you were driving on), or the map itself is the wrong one for the region. I realize that this last option is not likely when you are talking about real maps. I doubt you would try to find your way around New York using a map of Chicago. But this kind of thing happens all the time with worldviews. Sometimes the roads are wrong on otherwise good worldview maps. At other times, worldview maps are inadequate for the actual terrain.1He is making a grand point here. Many people make this simple mistake at the worldview level—a level which, as Koukl demonstrates below, can lead to undesirable social consequences.
Koukl explains a scenario in which Mother Teresa attempted to lobby for the forgiveness of a criminal. This demonstrates just how important the concept of the reductio is—it can have disastrous consequences in our thinking:
Mother Teresa once appealed to the governor of California to stay the execution of a vicious double murderer. She reasoned that since Jesus would forgive, the governor should forgive. Though the intentions were good, the argument itself proves too much, as our tactic demonstrates. When applied consistently, this view becomes a reason to forgo any punishment for any crime, because one could always argue, “Jesus would forgive.” Emptying every prison does not seem to be what Jesus would advise, since great evil would result. Capital punishment might be faulted on other grounds, but not on this one. Here is the analysis. Claim: If Jesus would forgive capital criminals, then it is wrong to execute them. Taking the Roof Off: On this reasoning, it would be wrong for government to punish any criminal, because one could always say, “Jesus would forgive.” This seems absurd, especially when Scripture states that the purpose of government is to punish evildoers, not forgive them.Therefore: Even though Jesus might forgive murderers, that does not mean it is wrong for the government to punish them.2In a final example from Greg, it becomes clear that such arguments can literally lead to the difference in mentality between life and death:
Virtually every argument in favor of abortion could equally justify killing newborns if pressed to its logical conclusion. If it’s acceptable to take the life of an innocent human being on one side of the birth canal, why forbid it on the other side? A seven-inch journey cannot miraculously transform a “nonhuman tissue mass” into a valuable human being. When someone justifies abortion by saying, “Women have the right to choose,” use a version of Taking the Roof Off called Trotting Out the Toddler. Ask if a woman should have the right to kill her one-year-old child for the same reason. Since both an unborn child and a one-year-old are human beings, the same moral rule should apply to each. The logic of choice, privacy, and personal bodily rights endangers newborns, not just the unborn. At the University of New Mexico, a student said we should abort children to save them from future child abuse. Former Stand to Reason speaker Steve Wagner “trotted out the toddler” in response. “Should we also kill two-year-olds to save them from future child abuse?” “I hadn’t thought about that,” the student said. And that’s the point. People don’t think about the logical implications of their ideas. It’s our job to help them see where their ideas logically take them.3A Monkey Wrench
I should point out one liability, here. Not everything that sounds contradictory actually is. In a few moments we’ll examine biblical examples of the reductio, some of which are employed by Jesus himself.
However, Jesus also taught paradoxical truths. Paradoxes are often surface-level contradictions that are not logically fallacious when examined closely. Many proverbs are like this as well. They are designed to create tension in your thinking for the purpose of making you dig deeper and think harder.
For example, when Jesus says, “He who is first shall be last,” he is saying something tha...
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