Based on the seminal work of Jean Piaget, cognition can be viewed
as progressing through 4 discrete stages. The first stage, termed sensorimotor, extends
from birth to approximately 18 months of age. During this period,
the child’s knowledge of the world is grounded in his or
her motor activities and sensory experiences. Coinciding with the emergence
of a sense of one’s existence as a separate human being,
children learn that objects exist even when they are no longer visible
(ie, “object permanence”), and they develop an
appreciation for the relation between actions and consequences (ie, “causality”).
The second stage of cognitive development, termed preoperational, generally
extends from 18 months to 7 years of age. The hallmark of this period
is development of the capacity for representational thinking, symbolic
functioning, and the emergence of fantasy in language as well as
in play. The “magical thinking” of the preschool
years results in delightful explanations of natural phenomena (eg, “rain
comes from God crying”) as well as the risk of viewing
illness as a punishment for misbehavior. The third cognitive stage,
termed concrete operational, typically extends
from ages 7 to 11 years. During this period, children are capable
of logical mental manipulations, and their thinking reflects an
ability to appreciate several dimensions of an issue at the same
time. For example, as demonstrated in Piaget’s classic
experiments, the school-aged child can understand that a short,
fat cup can hold as much water as a tall, thin glass. Finally, beginning
in early adolescence or later, the cognitive stage of formal
operations is reached. During this period, individuals
engage in abstract reasoning, which gives them the power to manipulate ideas
rather than remain restricted to the concrete world. For the reflective
adolescent and young adult, this provides a framework for passionate
discussions about morality, values, and philosophic principles.