<P> Children in this stage can, however, only solve problems that apply to actual (concrete) objects or events, and not abstract concepts or hypothetical tasks . Understanding and knowing how to use full common sense has not yet been completely adapted . </P> <P> Piaget determined that children in the concrete operational stage were able to incorporate inductive logic . On the other hand, children at this age have difficulty using deductive logic, which involves using a general principle to predict the outcome of a specific event . This includes mental reversibility . An example of this is being able to reverse the order of relationships between mental categories . For example, a child might be able to recognize that his or her dog is a Labrador, that a Labrador is a dog, and that a dog is an animal, and draw conclusions from the information available, as well as apply all these processes to hypothetical situations . </P> <P> The abstract quality of the adolescent's thought at the formal operational level is evident in the adolescent's verbal problem solving ability . The logical quality of the adolescent's thought is when children are more likely to solve problems in a trial - and - error fashion . Adolescents begin to think more as a scientist thinks, devising plans to solve problems and systematically test opinions . They use hypothetical - deductive reasoning, which means that they develop hypotheses or best guesses, and systematically deduce, or conclude, which is the best path to follow in solving the problem . During this stage the adolescent is able to understand love, logical proofs and values . During this stage the young person begins to entertain possibilities for the future and is fascinated with what they can be . </P> <P> Adolescents also are changing cognitively by the way that they think about social matters . Adolescent egocentrism governs the way that adolescents think about social matters, and is the heightened self - consciousness in them as they are, which is reflected in their sense of personal uniqueness and invincibility . Adolescent egocentrism can be dissected into two types of social thinking, imaginary audience that involves attention - getting behavior, and personal fable, which involves an adolescent's sense of personal uniqueness and invincibility . These two types of social thinking begin to affect a child's egocentrism in the concrete stage . However, it carries over to the formal operational stage when they are then faced with abstract thought and fully logical thinking . </P>

Which of the following is not one of the theorists who proposed a stage theory of development