Theory-of-Mind Training Causes Honest Young Children to Lie.

Theory of mind (ToM) has long been recognized to play a major role in children's social functioning. However, no direct evidence confirms the causal linkage between the two. In the current study, we addressed this significant gap by examining whether ToM causes the emergence of lying, an important social skill. We showed that after participating in ToM training to learn about mental-state concepts, 3-year-olds who originally had been unable to lie began to deceive consistently. This training effect lasted for more than a month. In contrast, 3-year-olds who participated in control training to learn about physical concepts were significantly less inclined to lie than the ToM-trained children. These findings provide the first experimental evidence supporting the causal role of ToM in the development of social competence in early childhood.