Prof. Pipe emphasized that children see a big difference between deceiving by telling lies and deceiving by keeping secrets. Keeping secrets does not require the child to say anything. Secrets involve a social contract which the child has made (agreeing not to tell). And children view most secrets positively-- for example, keeping a secret to give someone an exciting surprise.

Until about age four, children generally cannot keep secrets. This is because they have no “theory of mind,” as psychologists put it. This means that the child does not understand that what he or she knows is different from what other people know. Hence the child cannot grasp the idea of keeping his or her knowledge from another person.

Prof. Pipe explained that this does not mean that children younger than four cannot lie. Most every parent knows they do. According to psychologists, this happens because children learn that lying sometimes works; they do not learn why it works. Consider a child who does not like interrupting his play for diaper changes. He will likely discover that if he answers “No” to “Do you have a poopy diaper?,” he will often get to continue playing. He thus may begin giving that answer regardless of the condition of his diaper.