Are We Overly Credulous? No, It’s Just the Illusory Truth Effect

Illusory Truth Effect
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If you want people to believe something repeat it as often as you can and they’ll eventually rise to the bait. This is the core suggestion of a cognitive bias called the truth effect, or the illusory truth effect.

Even at the first thought it seems very naive to suggest this can be true. Yet it is true, moreover it’s confirmed by psychological research.

The repetition is often a key to making people believe what we want them to believe. The reason for this is people tend to consider things they hear permanently, or at least for several times, to be more plausible. On the contrary, they’d take everything new with a significant degree of skepticism and distrust.

Why Does It Happen and Is It Possible to Persuade Others in Anything You Want?

If people hear the same message again and again they are getting used to it. Our brain spends less time and effort on processing that information and takes it as truth just because it’s familiar. Psychologists name it cognitive fluency. When seeing familiar, easy recognizable objects we usually smile quietly, satisfied with the idea we know them and understand them.

The reverse is also true. People find it harder to believe in complicated things communicated to them just because the information is new and hard to understand. So it’d take their brains much more time to process it (with no guarantee they’ll get it eventually). It just proves once more that simplicity works best when it comes to explaining something (scientists should remember that).

It therefore follows it doesn’t really matter what is told to us: truth or lie. We’ll believe it as long as it’s repeated long enough. Hence the name of the bias – the illusory truth effect. Since the illusion of truth is often created and perceived easier than truth itself some think: it’s actually the frequency, not the plausibility that matters in the end.

The classic examples of the illusory truth effect in action are TV commercials, political campaigns, public figures’ opinions, etc. In other words, something which people are likely to hear or see at least several times a day.

At this point you might object that most people are sick of advertising and political agitation precisely because they hear them too often. You’re completely right of course.

When Enough Is Enough

A logical question arises: how many times can the message be repeated in order for people to believe it? Several studies showed people are most likely to believe the message after hearing it three to five times. After that they might get skeptical and contemptuous.

Repeating the data works well when people do not pay much attention to the subject. This means it’s better not to reiterate weak arguments to a competent, critical audience – they’ll spot it in an instance. On the contrary, strong arguments can be repeated frequently regardless of how smart the audience is – it will augment plausibility and lead people to thinking the information is true.


The illusory truth effect also has much to do with self-convincing. If we repeat the same thought, even irrational, for some time we actually end up believing it. It’s especially potent when the idea is already familiar to us, but was just hidden somewhere in the long-term memory. In that case we think it’s 100 percent true, as the fact we already know it (just forgot it) amplifies the impression of truth.

The illusion of truth shows us a very important fact: our mind makes little difference between illusions and truth. That’s why critical thinking can be only welcomed. Even back in the 17th century René Descartes wrote:

“If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.”

Read more on the other cognitive biases

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