The formal operational stage begins around the age of 12. This is the beginning of adolescence, a time of tremendous change in all areas of development. As Piaget points out, among the many changes associated with adolescence, there are significant cognitive changes as well. Primarily, the adolescent can effectively reason about the possible. While children in the concrete operational stage can reason about actual physical events, they are less effective when reasoning about potential or hypothetical events. In this way, concrete operational children are more restricted to the present or to the concrete.