Apprehending and attending to stimuli represents the first phase of thought. But for thinking to progress, the human brain must sort through the data at hand. The brain must establish similarities and differences and ultimately cluster the information into meaningful categories. Cognitive scientists refer to this sorting process as discrimination; they refer to the categorization of data as classification.
Accordig to cognitive scientists, human beings develop the ability to discriminate in early childhood (approximately two to seven years of age). The capacity to classify develops in middle to late childhood (approximately seven to eleven years of age). This timetable suggests certain critical differences in the cognitive life of the young. For example, suppose two children, one five years of age and the other ten years of age, are shown a grouping of objects—in this case, three apples and two oranges. Imagine next that the children are asked: Are there more apples or more oranges? Research indicates that both the five- and ten-year-old will answer the question correctly. Both possess the cognitive ability to discriminate between the two types of fruit. But suppose we ask a second question of the children: Are there more apples or more fruits? Research shows that the ten-year-old will answer the question correctly, while the five-year-old will likely be puzzled by the query. This is because the five-year-old lacks an advanced capability to which Jean Piaget referred as “the addition of classes” (Piaget 1952;1954). According to Piaget, classification involves more than an awareness of difference; the process requires one to understand that subclasses (e.g., apples and oranges) can be combined and transformed into a broader, more general class (e.g., fruits). Further, the ability to classify requires one to recognize that the general class (e.g., fruits) can be broken down or reversed into the original two subclasses (e.g., apples and oranges).