According to Piaget, young children go through two distinct phases or sub-stages in cognitive development during this stage. First, they develop Symbolic Function between the ages of 2 and 4. During the Symbolic Function sub-stage, children master the ability to picture, remember, understand, and replicate objects in their minds that are not immediately in front of them. In other words, children can create mental images of objects and store them in their minds for later use.
Before this period, during the Sensorimotor stage, infants and toddlers understood their world as containing only what they were immediately experiencing and nothing else. According to Piaget, if a toddler was playing with a kitten and it left his line of vision, the child would be unable to create a mental picture of that kitten. To the toddler, the idea of the kitten (and therefore the kitten itself) would no longer exist. Young children who have developed Symbolic Function can draw a picture of or pretend to play with a kitten that is no longer there.
These new cognitive abilities are helpful to young children's everyday experience. For example, children can talk about people who are traveling, or who live somewhere else, like Grandma in Florida. They can also talk about or draw places they visited, as well as create new scenes and creatures from their imagination. Children can also use their mental images of things to "play school" or to "play house."
Even though children in the Preoperational Stage have gained new cognitive skills, Piaget suggests that their thinking is rather rigid, limited to one aspect of a situation at a time, and strongly influenced by a item's appearance. This style of thinking, according to Piaget, leads to characteristic errors. For example, Preoperational children have not developed the mental abilities of Conservation and Transformation.
Conservation is a person's ability to understand that certain physical characteristics of objects remain the same, even if their appearance has changed. To demonstrate the concept of Conservation, Piaget showed young children two identical cups filled with identical volumes of water (reaching to the same measuring line). Preoperational youth agreed the cups had the same amount of liquid in them. Piaget proceeded to pour the liquid from one of the original cups into a wide, short cup. Then, he poured the liquid from the second original cup into a tall, narrow cup. When he asked Preoperational kids which cup had more liquid, they chose the taller cup. To these children, the taller cup looked like it had more volume even though the same amount of fluid filled both cups.
The concept of conservation can apply to number as well. For example, according to Piaget, a Preoperational child will not understand that rearranging six keys to make a different formation (e.g., spreading them out or moving them closer together) does not change the number of items present.
Transformation is a person's ability to understand how certain physical characteristics change while others remain the same in a logical, cause and effect sequence. According to Piaget, Preoperational Children do not readily understand how things can change from one form to another. To demonstrate this concept, Piaget first showed young children two 1-inch round balls of clay. Then, he presented the children with one 1-inch round ball of clay and one 1-inch ball of clay squished flat. A young person in the Preoperational stage would not understand that the flat ball had been round before and was squished to make its new shape.
Piaget also believed that Preoperational children have a style of thinking characterized by Egocentrism, or the inability to see the world someone else's point of view. According to Piaget, children with Egocentrism explain situations from their own perspective and understanding. Preoperational children also have a hard time understanding why banging on pots and pans or playing with a musical toy could increase their mother's headache when they're having so much fun.
According to Piaget, children in the Preoperational stage also believe that things are alive or have human characteristics because they grow or move, a style of thinking called Animism. For example, children may talk about cars like animals, as if they're growling or that they're hungry. Similarly, young children may blame chairs or toys for causing them to fall or trip. Finally, Piaget believes that children under the age of 4 don't have the ability to organize things into hierarchical categories. In other words, young children are unable to group items in larger sub-groups and smaller sub-groups based on similarities and differences.
Contemporary research suggests that Piaget's ideas about Preoperational children were not entirely correct; children in this stage of development vary greatly depending on their language skills, perceptual abilities, decision rules, and real-world knowledge. For example, when young children are tested using ideas and objects that are familiar to their everyday lives, they are better able to demonstrate their abilities. To illustrate: if a researcher uses a small number of objects (e.g., 3 instead of 6) to test conservation of number, 3-year-olds often notice that the number stays the same regardless of how it is arranged. Similarly, when young children are placed in a real world setting (e.g., their classroom), they are usually able to explain how other children (peers who sit in different seats) would see the room differently. Many young children can also group their toys into hierarchies (e.g., sorting animals vs. vehicles and then cars vs. trucks).
Contemporary developmental psychologists now believe that most children in Western cultures achieve conservation of number, length, mass and liquid between 6 and 7 years, even though conservation of weight may not occur until ages 8 through 10. Preoperational children often display egocentric thought, but, particularly toward the end of this stage, this style of thinking is not universal across all times and situations. Psychologists also think that animism is a way that children express their imagination and process how objects really work in a fashion that's easy for them to understand. Most children know that inanimate objects really aren't alive.