Reductio ad absurdum

Photo: Jurassic World (2015)

APOLOGIA        

By Hendrik van der Breggen

The Carillon, August 6, 2015

                

Reductio ad absurdum

               

Reductio ad absurdum is an argument strategy that employs logic to tease out the truth that another argument or claim is flawed. How? By reducing it to absurdity.

Let's look at this argument strategy in general terms, and then let's illustrate with a couple specific examples.

In a reductio ad absurdum argument, we assume, temporarily for the sake of argument, that the view under investigation is true. We approach the view in question with the attitude, "Okay, let's say it's true. What follows?" If the logical consequences of the view's assumed truth are false or logically contradictory, then it follows that the view under investigation is false or at least deeply problematic.

Here is an example from contemporary popular moral thought.

Consider the view that ethics is mere feeling, i.e., what's right and wrong is fundamentally a matter of subjective opinion or taste—there is no real right or wrong.

Let's say this is true, for the sake of argument. What follows logically?

If ethics is mere feeling, i.e., mere subjective opinion or taste, then right and wrong mean "I like" and "I don't like," respectively. Ethics becomes essentially similar to our attitudes to, say, food.

Just as I like chocolate ice cream rather than vanilla, you like vanilla rather than chocolate. No big deal. We're both right.

Cake: yum! Kale: yuck! Good: yum! Bad: yuck! This is the ethics-is-mere-feeling view.

But if the ethics-is-mere-feeling view is true (as we'll assume for the sake of argument), then another claim follows logically as true: just as Jane likes helping people and seeing them flourish, Joe likes torturing people and seeing them writhe in pain. So, if it's true that ethics is mere feeling, then Jane and Joe are both right ethically. No big deal.

Surely, though, that Jane and Joe are both right is clearly false (we know this via moral-rational insight). Hence, the assumption that ethics is mere feeling is flawed.

Here is another example from contemporary popular metaphysical thought (metaphysics has to do with the reality of being).

Let's say that personal identity, i.e., what I am, is wholly a personal matter—again, a matter merely of subjective feeling. My feelings about myself and my identity are trump.

Bruce (Caitlyn) Jenner basically holds this view. He feels he is a woman so he is a woman—and so he has had plastic surgery to "feminize" his face and throat, had hormone therapy for growth of breasts, and may yet undergo genital surgery to remove his testicles plus use his penis to construct a "vagina."

But if the view that my feelings about myself and my identity are trump is true, what follows?

It means that we must accept the claims of "otherkin" as true. Otherkin are people who self-identify as—i.e., who believe they actually are, at least in part or wholly—non-human. They believe they are cats, foxes, dragons, etc. If feelings are trump, then they are non-human in fact.

Moreover, it means we must accept the claim of Adrian Van Oyen, who in a YouTube "coming out" video, claims to be a dinosaur. Yes, a dinosaur. And, according to Van Oyen, if you don't accept him for who he is, you are "transdinophobic."

(Note: Van Oyen's two-minute video is a stunt, ending with an image of a "facepalm" to the forehead; nonetheless, it makes an insightful philosophical point.)

Surely, however, the alleged truth of the thesis that my feelings about myself and my identity are trump lands us logically into obvious absurdities and falsehoods. Regardless of what a man feels, he is in reality not a dinosaur, nor a cat, nor a woman.

Feelings are not trump. Reductio ad absurdum.

Objective truth and reality are trump.

(Hendrik van der Breggen, PhD, is associate professor of philosophy at Providence University College. The views in this column do not always reflect the views of Providence.)

ADDENDA

A. Here are a couple  interesting reductio-ad-absurdum-related bits located here because of space limitations in the main body of my column:

1. If my feelings about myself and my identity are trump, then we should also accept the claims of the "transabled." The transabled are people who feel that they are imposters if their body is in full working order, so they seek to amputate a limb or otherwise mutilate/ disable themselves. But the truth is that you are not in fact an imposter if your body is in full working order. Again, the alleged truth of the thesis that my feelings about myself and my identity are trump lands us logically into obvious absurdities and falsehoods.

2. The Bible is no stranger to logic (which makes good sense because God is the Logos). In fact, the reductio ad absurdum is employed in the New Testament. Paul preaches the resurrection of Jesus (which he and others know to be true) and Paul addresses those who say there is no resurrection of the dead. He argues "if there is no resurrection of the dead, then not even Christ has been raised" (1 Cor. 15:13). But Paul adds that he testifies to Christ being raised: "Christ has indeed been raised from the dead" (1 Cor. 15:20a). That is, Paul and others know this to be true. D.J. Hill, in New Dictionary of Apologetics, concludes: "So, Paul shows that the assumption that there is no resurrection leads to the contradiction that Christ has both been raised and not raised from the dead." In other words, in view of the known fact that Jesus was in fact raised from the dead, the claim that there is no resurrection reduces to the absurd.

B. For further discussion of reductio ad absurdum arguments, see:

1. Julian Baggini & Peter S. Fosl, The Philosopher’s Toolkit: A Compendium of Philosophical Concepts and Methods, 2nd edition (Oxford: Wiley-Blackwell, 2010), 121-122.

2. D. J. Hill, “Reductio Ad Absurdum,” in New Dictionary of Christian Apologetics, edited by W. C. Campbell-Jack & Gavin McGrath (Downers Grove, Illinois: IVP Academic, 2006), 602-603.