In the 1960s and 1970s, as Freudian and Jungian psychology were rapidly being replaced with more empirical methods of studying human behavior, a Swiss philosopher and psychologist named Jean Piaget stepped in to offer a new experimentally-verified theory of development. Like Freud, Piaget thought that human development could be described in stages. Unlike Freud, however, Piaget did not believe that growth and learning were driven by repressed sexuality. Rather, in his experiments with children, adolescents, and young adults, Piaget learned that as we grow, we gradually add new skills to our cognitive repertoire. He described four stages of cognitive development, which are presented below.
Sensorimotor Stage: Children at the sensorimotor stage are explorers. They want to see, hear, taste, and touch everything around them. The generally do not appear to be thinking about what they do – no obvious rationale underlies their motives. Instead, they are reveling in sensory experience and enjoying their own rapidly-improving abilities to move around and take in new experiences. Language at this stage is used for primarily for cataloguing objects in the child’s environment (“doggie!” “truck!”) and for making demands of his or her caregivers. Sensory stimuli are paired up with voluntary motor responses, and sensory/body coordination is established. Syntax and grammar have not yet been developed, and relations between concepts are vaguely understood at best. It is during the late sensorimotor stage that children learn the concept of “object permanence”: in other words, they learn that objects still exist even if they cannot see them.
Preoperational Stage: Around age 2, children enter the preoperational stage, where they will learn how to think abstractly, understand symbolic concepts, and use language in more sophisticated ways. During this stage, children become insatiably curious and begin to ask questions about everything they see. They can imagine people or objects that do not exist (such as a lizard with wings) more readily than younger children, and they like to make up their own games. Preoperational children understand object permanence, but they still do not have the concept of conservation: that is, the idea that changing a substances appearance does not change its properties or quantity. Piaget famously poured two identical glasses of water and asked children to tell him if they had the same amount of water or not. Of course, the children replied that they were equal. Piaget then poured the contents of one glass into a tall, narrow beaker and repeated the question. This time, children said there was more water in the cylinder because it was taller.
Concrete Operational Stage: By the time they are 7 years old, children can understand much more complex abstract concepts, such as time, space, and quantity. They can apply these concepts to concrete situations, but they have trouble thinking about them independently of those situations. Their ideas about time and space are sometimes inconsistent, but a basic logic is present that governs their cognitive operations. Children can learn rules fairly easily, but may have trouble understanding the logical implications of those rules in unusual situations. In other words, they do not have an abstract “concept” of the rule distinct from its application in a specific context.
Formal Operations Stage: Children around age 11 start to become capable of more abstract, hypothetical, and theoretical reasoning. They can apply rules to a variety of situations, and can engage in counterfactual “if-then” reasoning. “Counterfactual” refers to the fact that the “if” is known not to be true, for example “if dogs were reptiles, they would have cold blood.” A child in the formal operations stage can accept this as valid reasoning, even though the premise is obviously false. At this stage, formal logic becomes possible and verbal explanations of concepts are usually sufficient without demonstration. Strategy-based games become more enjoyable, whereas rote games like “chutes-and-ladders” become repetitive.