the moon and stars follow him on a night walk. Upon learning that such is the case for his friends, he must separate his self from the object, resulting in a theory that the moon is immobile, or moves independently of other agents. The second stage, from around three to eight years of age, is characterized by a mix of this type of magical, animistic, or "non-natural" conceptions of causation and mechanical or "naturalistic" causation. This conjunction of natural and non-natural causal explanations supposedly stems from experience itself, though Piaget does not make much of an attempt to describe the nature of the differences in conception. In his interviews with children, he asked questions specifically about natural phenomena, such as: "What makes clouds move?", "What makes the stars move?", "Why do rivers flow?" The nature of all the answers given, Piaget says, are such that these objects must perform their actions to "fulfill their obligations towards men". He calls this "moral explanation". Postulated physical mechanisms underlying schemas and stages In 1967, Piaget considered the possibility of RNA molecules as likely embodiments of his still-abstract schemas (which he promoted as units of action)—though he did not come to any firm conclusion. At that time, due to work such as that of Swedish biochemist Holger Hydén, RNA concentrations had, indeed, been shown to correlate with learning. Practical applications Parents can use Piaget's theory in many ways to support their child's growth. Teachers can also use Piaget's theory to help their students. For example, recent studies have shown that children in the same grade and of the same age perform differently on tasks measuring basic addition and subtraction accuracy. Children in the preoperational and concrete operational levels of cognitive development perform arithmetic operations (such as addition and subtraction) with similar accuracy; however, children in the concrete operational level have been able to perform both addition problems and subtraction problems with overall greater precision. Teachers can use Piaget's theory to see where each child in their class stands with each subject by discussing the syllabus with their students and the students’ parents. The stage of cognitive growth of a person differ from another. Cognitive development or thinking is an active process from the beginning to the end of life. Intellectual advancement happens because people at every age and developmental period look for cognitive equilibrium. To achieve this balance, the easiest way is to understand