Illusory truth effect
The illusory truth effect is the tendency to judge a statement as more likely to be true simply because it has been heard or read before. Repetition makes a claim feel familiar, and that familiarity is mistaken for accuracy.
- 1 min read
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Why does the illusory truth effect happen?
Repeated statements are easier to process, and the mind uses that ease, called processing fluency, as a shortcut for truth. Most of the time the shortcut works, because true things tend to be repeated more often than false ones. But the brain does not check why something feels familiar, so a falsehood repeated in adverts, headlines or a social feed earns the same unearned credibility. Fazio and colleagues found that even prior knowledge of the correct answer does not fully protect people, since fluency can override what they know.
What does the illusory truth effect look like in real life?
- A health myth shared repeatedly online starting to sound like common sense.
- An advertising slogan heard dozens of times making a product claim feel established.
- In Hasher, Goldstein and Toppino’s 1977 study, plausible trivia statements were rated more likely to be true when they reappeared across sessions.
How do you counter the illusory truth effect?
- When a claim feels obviously right, ask whether you know it or have merely heard it often.
- Check the source of familiar claims before repeating them, especially on social media.
- When correcting a myth, lead with the accurate fact rather than restating the falsehood prominently.
Frequently asked
- What is the illusory truth effect in simple terms?
- If you hear something often enough, it starts to feel true, whether it is or not. Familiarity creates a sense of rightness, and people tend to read that feeling as evidence.
- Who discovered the illusory truth effect?
- Lynn Hasher, David Goldstein and Thomas Toppino reported it in 1977. Participants rated trivia statements over several sessions, and those that had been repeated were judged more likely to be true than new ones.
- Does knowing the truth protect you from the illusory truth effect?
- Only partly. A 2015 study by Lisa Fazio and colleagues found that repetition increased belief in false statements even when participants could have answered correctly from their own knowledge.
- Illusory truth effect vs mere-exposure effect?
- The mere-exposure effect is liking something more because it is familiar. The illusory truth effect is believing a statement more because it is familiar. Both rest on familiarity, but one shapes preference and the other shapes belief.
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Cite this page
ReadGlobe. (2026). Illusory truth effect. https://readglobe.com/bias/illusory-truth-effect/
"Illusory truth effect." ReadGlobe, 24 Oct. 2026, readglobe.com/bias/illusory-truth-effect/.
Editorial synthesis © ReadGlobe 2026, drawing on Kahneman’s Thinking, Fast and Slow, the Tversky–Kahneman research program, and the primary cognitive-science literature. · Last reviewed 2026-10-24.