The Power of Repetition: Propaganda and Persuasion, Part 3

by Patricia Engler on June 9, 2021

Repeating a lie can’t make it true, but repetition certainly makes for effective propaganda. Here are some studies showing the power of repeated messages and—in a surprise twist relevant to mentorship—how repetition affects students and seniors differently.

Which of these often-repeated sayings is a real Bible verse?

  1. God works in mysterious ways.
  2. Money is the root of all evil.
  3. Be in the world but not of the world.
  4. Cleanliness is next to godliness.

These statements can ricochet around Western church circles with such abandon, it may come as a surprise that none of them is written in the Bible. Some of them are close to Bible verses; for instance, 1 Timothy 6:10 (ESV) states that the love of money is a root of all kinds of evil. And being in the world but not of the world is a biblical concept, rooted in passages like John 17:14–16; Romans 12:2; and 1 John 2:15. But I’ll admit, I had to take a few minutes to verify when someone told me this “verse” I’ve heard quoted so often is not a direct line from Scripture.

Whether pseudo-Bible verses, advertising slogans, or well-known “facts” that are really myths, messages can sound true just because we’ve heard them over and over. If we stop and think about it, we know that no amount of repetition can make a false statement true. To believe otherwise would be to fall for a fallacy—a faulty form of logic—known as argument from repetition, or ad nauseum.

Despite being illogical, arguments from repetition make for persuasive propaganda.1 Why are repeated messages so compelling—and so able to mislead? To find out, let’s dive into a little brain science.

How Repetition Tricks the Brain

In an earlier post, I mentioned that the human brain tends to fall into a faulty thinking pattern (cognitive bias), called the illusionary truth effect, where a message sounds true because it’s repeated often. This bias stems from two related heuristics, or mental shortcuts the brain uses to make automatic decisions:2

  1. The recognition heuristic is our tendency to make snap decisions about something based on whether we recognize it, with more familiar objects typically seeming more likable and trustworthy.
  2. The fluency heuristic is our tendency to make snap decisions based on how quickly our brains can process the relevant information.

Messages we’ve heard before are easier to process—and so are messages that simply “make sense.” Messages that make sense are often true, so the brain tends to automatically associate processing ease, or fluency, with truth. For instance, studies have found that people are more likely to rate messages as true when they’re written in easy-to-read font colors.3 Fluency also helps explain why messages that are clearly and eloquently communicated can sound truer, because they’re easier to understand.

For instance, as a student, I noticed that some of my evolutionary professors communicated so eloquently, their words sounded true—even though the way a message comes across is irrelevant to whether it’s true. This highlights the trouble with relying on fluency: messages that are easy to process aren’t always logical.

Repetition Research

However illogical, repetition remains an effective propaganda technique because—as multiple studies confirm—the illusionary truth effect is remarkably powerful.4,5 Some research suggests this effect packs even more punch when we hear the same (false) message repeated by different sources.6 For instance, the statement that birds evolved from dinosaurs over millions of years may sound convincing because we hear it from various sources including museums, textbooks, and movies. However, this is an interpretation about the unobservable past—one with marked issues from observational science.

Originally, most researchers assumed that people would be less susceptible to the illusionary truth effect if they already knew a repeated message was false. But in 2015, a study showed otherwise.7 Students read true or false statements, half of which they’d seen before, and ranked the statements’ validity on a scale ranging from definitely true to definitely false. Then, the students answered questions revealing their prior knowledge about the information those statements covered. Results revealed that on average, students always gave repeated lies a higher truth score than lies they’d never seen before, even when the prior knowledge test showed that the students KNEW those statements were false!

After further study, the researchers concluded that students are more likely to rely on fluency first, above prior knowledge, when evaluating messages. Opposite of what most researchers once assumed, students typically use their prior knowledge to evaluate messages only when relying on fluency and repetition isn’t an option.

But amazingly, a similar experiment in 2017 with both students and seniors above age 65 found that, while repetition trumped knowledge in young adults, seniors relied on prior knowledge more and only used the fluency heuristic when they didn’t already know whether a message was true.8 The researchers suggested this is because seniors have had more time to become familiar with what they know, making their knowledge easier to retrieve.

Take-Home Lessons:

These findings offer just one more example of why Christian youth need connections with older adult mentors—not despite the fact that older adults may think differently from young people, but precisely because of it. As another practical takeaway, when I shared this research with a group of teenagers, one of them pointed out how the power of repetition connects to Christians’ need for media discernment. That is, understanding that repeated messages do have an effect on our minds reminds us as Christians to exercise wisdom when choosing the media—and associated messages—we consume.9

On the flip side, if we regularly fill our minds with God’s Word, which we know is true,10 we’ll be far more ready to use that truth to combat repeated unbiblical messages in today’s classrooms and culture. Plus, we’ll be pros at spotting fake Bible verses.


  1. Propaganda is a manipulative form of communication which tries to persuade by appealing to something other than logic. Propaganda can be used to promote good causes and true messages; the trouble comes when the main persuasive power of a message lies in factors besides the message’s content. (This is especially prone to happen in messages which have limited logical basis, so must be promoted primarily by propaganda.)
  2. Ralph Hertwig et al., “Fluency Heuristic: A Model of How the Mind Exploits a By-Product of Information Retrieval,” Journal of Experimental Psychology: Learning, Memory, and Cognition 34, no. 5 (2008): 1191.
  3. Christian Unkelbach, "Reversing the Truth Effect: Learning the Interpretation of Processing Fluency in Judgments of Truth," Journal of Experimental Psychology: Learning, Memory, and Cognition 33, no. 1 (2007): 219.
  4. Alice Dechêne et al., "The Truth About the Truth: A Meta-Analytic Review of the Truth Effect," Personality and Social Psychology Review 14, no. 2 (2010): 238–257.
  5. Some research suggests the illusionary truth effect isn’t as strong if people know the message source is unreliable. (Christian Unkelbach and Christoph Stahl, “A Multinomial Modeling Approach to Dissociate Different Components of the Truth Effect,” Consciousness and Cognition 18, no. 1 (2009): 22-38.) However, the brain is more likely to remember a message’s content than its source over time, so the researchers found that after 2–3 weeks, the illusionary truth effect reappeared as people forgot the message source. (Linda Henkel and Mark Mattson, “Reading Is Believing: The Truth Effect and Source Credibility,” Consciousness and Cognition 20, no. 4 (2011): 1705–1721, cited by Lisa Fazio et al. (2015).)
  6. Hal Arkes, Lawrence Boehm, and Gang Xu (1991), “Determinants of Judged Validity,” Journal of Experimental Social Psychology 27, no. 6 (1991): 576–605, cited by Christian Unkelback (2007). (See also Christian Unkelbach and Christoph Stahl, 2009.)
  7. Lisa Fazio et al., “Knowledge Does Not Protect Against Illusory Truth,” Journal of Experimental Psychology: General 144, no. 5 (2015): 993.
  8. Nadia Brashier et al., “Competing Cues: Older Adults Rely on Knowledge in the Face of Fluency,” Psychology and Aging 32, no. 4 (2017): 331.
  9. Highlighting the significance of media consumption choices, a recent study by Barna researchers who identified a thriving biblical worldview in only 10% of American Christian young people found that individuals within that 10% tended to not only rack up less “screen time,” but also to allocate proportionately more of their screen time to viewing solid Christian content. (David Kinnaman and Mark Matlock with Aly Hawkins, Faith for Exiles: 5 Ways for a New Generation to Follow Jesus in Digital Babylon, e-book ed. (Grand Rapids: Baker Books, 2019), accessed on Hoopla, 138–147.)
  10. To answer why it’s not circular reasoning to defend God’s Word from the foundation of God’s Word, see Darius Viet and Karin Viet, “Circular Reasoning,” Answers in Genesis, May 27, 2011, or Critical Thinking Scan Season 2, Episodes 9–10 on Answers TV.


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