Conservation (Psychology)

Conservation, in Piagetian developmental psychology, is the understanding that a given quantity of a substance, such as its number, mass, length, area, or volume, stays the same even when its outward shape or arrangement is changed, so long as nothing has actually been added or taken away. The Swiss psychologist Jean Piaget identified the concept through a series of now-classic tasks: in the best-known version, a child watches liquid poured from a short, wide glass into a tall, narrow one and is asked whether the amount of liquid has changed, and a child who has not yet grasped conservation typically insists there is now more liquid because the level looks higher, focusing only on the single dimension of height rather than on both height and width together. Piaget proposed that the acquisition of conservation marks the transition from the preoperational stage, roughly ages two to seven, in which children's thinking is dominated by how things appear on the surface, into the concrete operational stage, roughly ages seven to eleven, in which children become capable of logical mental operations, including reversibility, the recognition that pouring the liquid back into its original container would restore the original appearance. Piaget documented that children typically master conservation of number and length somewhat earlier than conservation of mass, and conservation of mass earlier than conservation of volume, a staggered developmental sequence sometimes called horizontal decalage, and later researchers have shown that conservation performance can be improved or impaired by the specific wording and social framing of the task itself, indicating the underlying competence often develops earlier than Piaget's original testing method was able to detect.