According to developmental psychologists, three types of knowledge determine a child’s understanding of the world: intuitive physics, intuitive psychology, and with certain reservations, intuitive biology. Part of this knowledge is characterized as core knowledge, that is, knowledge that children learn without instruction; for example, intuitive comprehension of physical, biological, and psychological entities as well as different forms of processes in which these entities engage. Core knowledge — developed by preschool age — provides the foundation for further development. It is based on what psychologists call domain specialized learning mechanisms, or modules, which evolved in response to our Paleolithic environment.
Developmental studies show that core knowledge of physical entities includes the understanding that the world is composed of material objects which have volume and an independent existence in space. Core knowledge of biological entities represents a species-typical adaptation to the problem of food selection and illness avoidance. Even if cultures lack a scientific understanding of disease transmission they still possess an intuitive understanding of it through their core knowledge. Similarly, 4-year-olds know that abnormal behaviors are not contagious, and they can discriminate between contaminated and safe substances despite a lack of visible evidence. Core knowledge of psychological entities includes the understanding that animate beings are intentional agents which have a mind. By the middle of the second year children understand that animate beings can reciprocate actions and have a capacity to move and initiate actions without external force. In addition, small children understand that the contents of mind — thoughts, beliefs, desires, and symbols — are nonmaterial and mental, and that they do not contain the properties they stand for.