https://doi.org/10.1177/0963721419827854 Current Directions in Psychological Science 1–7 © The Author(s) 2019 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/0963721419827854 www.psychologicalscience.org/CDPS ASSOCIATION FOR PSYCHOLOGICAL SCIENCE It was Napoleon, I believe, who said that there is only one figure in rhetoric of serious importance, namely, repetition. The thing affirmed comes by repetition to fix itself in the mind in such a way that it is accepted in the end as a demonstrated truth. Gustave Le Bon (1895/1996, Chapter 3.2) Judging the truth of information is one of the most important tasks people face every day. Subjectively true information influences opinions (e.g., “Do vaccinations cause autism?”), judgments (e.g., “I do not believe that vaccinations cause autism”), and choices (e.g., “I will vaccinate my child”). In a world of “alternative facts” and “fake news,” it is paramount to understand the psychological processes by which people come to believe information. Here, we discuss one of the most robust influences on subjective truth: repetition. People believe repeated information more than novel informa- tion, a phenomenon called the repetition-induced truth effect. The following describes the effect and its psychologi- cal explanations with an emphasis on recent theoretical and empirical developments. We close with potential implications of truth by repetition for an information environment in which people are exposed to repeated but potentially harmful false information. The Repetition-Induced Truth Effect In a typical experiment, individuals read or hear infor- mation once in a presentation phase (e.g., “The highest tree in the world is a spruce”). After some delay, they complete an evaluation phase, in which they judge the truth of the presented information. Importantly, partici- pants evaluate repeated information from the presenta- tion phase and novel information. People typically evaluate repeated information as more true compared with novel information, and if information is also evalu- ated during presentation, truth evaluations increase because of repetition for a given information item. The change in subjective truth is captured by rating scales or binary true/false choices. For example, Hasher, Gold- stein, and Toppino (1977) asked participants to evaluate statements on a 7-point scale (1 = definitely false, 2 = probably false, 3 = possibly false, 4 = uncertain, 5 = 827854CDP XX X 10.1177/0963721419827854Unkelbach et al.Truth by Repetition research-article 2019 Corresponding Author: Christian Unkelbach, University of Cologne, Social Cognition Center Cologne, Richard-Strauss-Strasse 2, 50931 Köln, Germany E-mail: christian.unkelbach@uni-köln.de Truth by Repetition: Explanations and Implications Christian Unkelbach 1 , Alex Koch 1 , Rita R. Silva 1 , and Teresa Garcia-Marques 2 1 Social Cognition Center Cologne, University of Cologne, and 2 William James Center for Research, ISPA, Instituto Universitário Abstract People believe repeated information more than novel information; they show a repetition-induced truth effect. In a world of “alternative facts,” “fake news,” and strategic information management, understanding this effect is highly important. We first review explanations of the effect based on frequency, recognition, familiarity, and coherent references. On the basis of the latter explanation, we discuss the relations of these explanations. We then discuss implications of truth by repetition for the maintenance of false beliefs and ways to change potentially harmful false beliefs (e.g., “Vaccination causes autism”), illustrating that the truth-by-repetition phenomenon not only is of theoretical interest but also has immediate practical relevance. Keywords truth effect, repetition, fake news, alternative facts, belief formation, referential theory, familiarity, fluency