The Illusory Truth Effect: How a Repeated Lie Becomes the Truth

The illusory truth effect speaks of the vulnerability of our cognitive system. In fact, it can be manipulated by others by the simple process of repetition.
The Illusory Truth Effect: How a Repeated Lie Becomes the Truth
Sergio De Dios González

Written and verified by the psychologist Sergio De Dios González.

Last update: 26 October, 2022

The phrase “A lie told a thousand times becomes the truth” was attributed to Joseph Goebbels, Hitler’s propaganda minister. It described a chain of events. This is due to a psychological process known as the illusory truth effect, or the reiteration effect.

Aldous Huxley, in his book, Brave New World, also referred to the illusory truth effect. In this novel, one of the mechanisms used by power to influence society was to make people listen to a statement 62,400 times while they slept.

Furthermore, we all know that the illusory truth effect is one of the most exploited by the advertising industry to gain influence. It occurs because repetition makes the brain familiar with certain statements. Therefore, it ends up assimilating them as if they were true, even if they’re not. Let’s see how it works.

A reliable way to make people believe in falsehoods is repetition, because familiarity is not easily distinguished from the truth .”

-Daniel Kahneman-

friends talking
The effect of truth by repetition makes us accept as true something that’s repeated to us frequently.

The illusory truth effect

The illusory truth effect is a psychological mechanism by which we tend to give subjective validity to what’s frequently reiterated to us. It’s a bias that operates because we don’t tend to compare what we might be told with the evidence or the facts. Thus, listening to a message many times makes us internalize the idea that it’s validated by many others.

Our cognitive system is paradoxical. W e tend to give the nature of truth to certain statements. In fact, we take as reference certain data that may not have anything to do with the supporting facts.

Sometimes, a statement reaffirms our own beliefs. At other times, it’s a ‘truth’ believed by many others and thus given credibility by us. In fact, some claims, even if they turn out to be far-fetched, we can end up accepting as true on the strength of repetition.

One of the most interesting aspects is that we come to believe implausible data, not only about subjects we know little about, but about those we’re already familiar with.

A revealing investigation

An investigation conducted by the Catholic University of Louvain  (Belgium) examined various aspects of the phenomenon of the illusory truth effect. They enlisted 200 volunteers, who were exposed to several false statements.

In the first phase, the participants were made aware of a series of statements that, in the light of reason, were preposterous. For instance, that the Earth was square or that smoking was good for the lungs. There were between eight and 16 statements. Participants were asked to rate how believable each statement was. Then, they were presented with them again in another order and so on, until they’d completed them five times.

In the second phase, they were again shown 16 statements. Eight of them had already been used in the previous phase and the other eight were new. They had to rate them from one to 50, where one was ‘definitely false’ and 50, ‘definitely true’. Then, it was evaluated if the repetitions had generated any change in the perception of the participants.

The findings indicated that 53 percent of people viewed repeated claims as increasingly less false. On the other hand, 28 percent, had the opposite effect, and the more the participants were exposed to repetitions of absurd ‘truths’, the more aware they were of their falsity. Therefore, the illusory truth effect doesn’t seem to always work.

Blue lit brain
When something sounds familiar to us or we’ve heard it several times, the brain can take it for granted and thus save itself energy.

Brain traps

The phenomenon of the effect of the illusory truth effect doesn’t operate for its own sake. The answer lies in a trap in the brain. The truth is that this organ isn’t exactly a monument to diligence. Quite the contrary: the brain is somewhat lazy and saves energy whenever it can.

Thus, repetition means more ‘processing fluidity’, making the information easier to process. The effect is similar to when we read a complex text. With each new reading, we usually manage to understand it a little better. This fact tends to suggest that the study data is true. When something ‘resonates with us’, our brains tend to be less critical. In other words, we lower our guard and accept the data without examining it thoroughly, since this saves work.

There are some people who are more likely not to evaluate any information they receive. Taking this into account, along with the tendency of the brain to work less, the perfect circumstances appear for us to end up believing that any lie can be true if it’s repeated enough times. That’s how the illusory truth effect works.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

  • Concha, D., Bilbao Ramírez, M. Ángeles, Gallardo Cuadra, I., Páez Rovira, D., & Fresno Rodríguez, A. (2016). Sesgos cognitivos y su relación con el bienestar subjetivo. Salud & Sociedad3(2), 115-129.
  • Lacassagne, D., Béna, J., & Corneille, O. (2022). Is Earth a perfect square? Repetition increases the perceived truth of highly implausible statements. Cognition, 223, 105052.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.