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How to Challenge Your Opponent’s Evidence. Use The Three Rs

“People generally quarrel because they cannot argue.” – G.K. Chesterton

People often make one of two mistakes when they imagine what an argument is. They either underthink it, which means they think an argument is just two or more people disagreeing with each other, perhaps in the form of a “fight” or shouting match. 

Or, they overthink it, which means they think argumentation is just too advanced and complex. Perhaps they’ve seen debaters in action, and they’ve been discouraged by all of the jargon: “status quo,” “burden of proof,” “warrant,” “topicality,” “solvency,” “inherency.” Huh? 

Argumentation does require some skill, but it is not just for professionals. In fact, not only can you learn argumentation, you should

Imagine if you found out your city government was making decisions based on a coin toss, a personal vendetta, or a sense of divine revelation. This would justifiably unsettle you. As communication scholars Edward Schiappa and John P. Nordin point out, learning how to argue is an essential skill both for personal advancement and democratic life. We should all learn the skills. 

That’s why in this short series of blogs, I am covering a number of key skills related to argumentation, skills like the three parts of an argument, the three-step persuasive sequence, and these rebuttal strategies

But at its most basic level, argumentation is a matter of evidence. Who has the most and the best evidence to back their opinion? Use the following three Rs to evaluate your own evidence and to challenge the evidence of your opponent: 

  1. Is the evidence reliable?
  • Reliability means the evidence comes from a source that is both expert and objective. If your opponent is arguing against gun regulations, and they cite a source from the National Rifle Association, then you can claim their evidence is not objective. It doesn’t mean their source is wrong about the evidence. It just means the source lacks reliability. Similarly, if your opponent cites a movie star or even a scholar who does not do work in the subject area being argued, their evidence lacks expertise, which means it may not be reliable. 
  • Reliability also means the evidence comes from a method that is considered to be rigorous. Studies with sample sizes that are too small, or that ignore competing evidence, or that have not been reviewed by qualified experts, or that have not been replicated by additional studies may not be reliable.  
EXAMPLE:  In my own field, there is the famous and infamous 7% rule. This is the belief that only 7% of the impact you have on your audience comes from your content. The other 93% comes from the way you look and sound when you communicate. Literally for decades, these percentages have been shared with trusting audiences by experts in the field of communication. But in fact, Albert Mehrabian, the UCLA researcher whose study came up with these percentages, admitted that the study was not very reliable. His sample size was tiny, consisting only of a handful of women (no men); it addressed only a particular kind of communication; it used only single words rather than whole messages in its experiments, and other studies have come up with different numbers. In short, Mehrabrian’s research is little more than an experimental anecdote. It can be helpful in certain contexts, but it is not universally reliable.   
  1. Is the evidence recent
  • Imagine that your opponent is making claims about mental illness and suicide rates among teens, but their research is pre-2015. It was only after about 2015 that researchers began to publish regularly on a steady upward trend of mental illness among teens, which demonstrated strong correlations with the introduction of the smartphone and increases in screen-based activities. 
  • There are certain forms of evidence that are less constrained by time. For instance, evidence that smoking increases cancer risk is not likely to become obsolete. However, most debates about current events rely on the most recent evidence. If your opponent is not drawing on that evidence, they have a weakness. 
  1. Is the evidence relevant
  • When evidence is relevant, it directly supports the claim being made. When your opponent makes a claim, then provides evidence that does not sufficiently support their claim, it means their claim is unwarranted. You’ve probably heard the terms “warranted” and “unwarranted” before. Most people assume that when we say a claim is warranted, we simply mean it has evidence. But more accurately, the term means the evidence has been shown to support the claim. It has been explained in such a way that the evidence and claim are now bound together. 
  • Another test of relevance is to make sure that the evidence comes from research that can be applied to the situation at hand. For instance, a crime prevention policy that worked in Sweden might not work in Texas. A marketing campaign that worked for a bowling alley in Peoria might not work for a mall in Salt Lake City. 
EXAMPLE CONTINUED: The Mehrabian example with the 7% rule is, technically, evidence. After all, it is based on a real study conducted by a real scholar. But as I pointed out above, it lacks rigor and replication. But it also is guilty of the other two cardinal sins discussed in this article. It was conducted in the 1970s, so it is not recent. Can we know that these same interpersonal rules apply? In the digital age, perhaps certain interpersonal communication practices have evolved. But worst of all, the Mehrabian research does not merit the claims being made by a lot of communication experts. Because of the study’s limitations, the evidence isn’t entirely relevant. Therefore, the claims being made are unwarranted. Again, the Mehrabian study can be useful in specific contexts, but because of its weaknesses in reliability, recency, and relevance, it can easily be rebutted by a smart debater. 


One of my pet peeves is when people simply say “research shows” or “studies show.” I am guilty of using this phrasing myself every so often, particularly if I am pinched for time. However, if I am in a serious debate, this kind of phrasing is unacceptable. A good debater won’t let their opponent get away with it. They will ask their opponent questions like, “Which studies?” “By whom?” “When and where were they conducted and published?” “Were they peer-reviewed?” “Who or what were their subjects in the study, and are those subjects like the subjects we’re debating now?” “Have their findings been replicated?” 

Another pet peeve of mine is the phrase “the evidence speaks for itself.” Plenty of research will show that, in fact, the evidence does not speak for itself. I like the recent work of Douglas Alchin, who calls this phrase a “Sacred Bovine” in public debates. His work shows that even in a hard science like Biology, the evidence does not speak for itself. 

Knowing how to ask questions of the evidence, even if and when you think your opponent is using good evidence, can open up a lot of new possibilities. Not only might questions reveal unexpected weaknesses in your opponent’s evidence, but they may give you time and ideas for creating new critiques and counterarguments. And for the record, asking tough questions will also make you look smarter. That never hurts.   

Ben Crosby is a professor of rhetoric and a communication skills consultant. He teaches courses in public speaking and presenting, argumentation and debate, technical and professional communication, persuasion and selling, and the history of rhetoric.

His work is regularly published in his field’s top academic journals and conferences. He is also the author of Presentations as Performance: A Professional’s Guide to Better Speaking.

Ben’s areas of expertise are Public Speaking, Presentation Skills, Argumentation, Sales Training, and Professional Writing.

In his free time, he spends time with his wife, Rebecca, their four kids, and their cat, Arza. He is an avid Utah Jazz fan. 

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