So how exactly do psychologists go about measuring how people think about their own thoughts and thoughts of others? One of the most commonly used methods to assess a child’s theory of mind abilities is known as a false-belief task. The ability to attribute false belief in others is considered a major milestone in the formation of a theory of mind.
The goal of such tasks is to require children to make inferences about what someone has done or what they are thinking when the other person’s beliefs about reality are in conflict with what children currently know. In other words, children may know something is true; an understanding of false belief requires them to understand that other people may not be aware of this truth.
For example, a child might know that there are no cookies left in the cookie jar—but does he understand that his sister has no way of knowing that there are no cookies left?