Concepts are general ideas or terms that can be used to group objects, situations, qualities, or abstractions, that let them become equal in a certain way.How can the who and what be understandable?How to divide objects into categories? Children use categorical hierarchy to distinguish between categories. The categories are classified into set-subset relation, such as animal-dog-poodle. Small children especially use perceptual categorization: grouping objects that are similar. It can already be seen in children from 3 to 4 months old. As children grow older, they also understand hierarchical and causal relationships between categories. The categorical hierarchies’ children are forming often contain three levels: the superordinate level (for example a plant), the subordinate level (for example an oak tree), and the basic level (for example, a tree). Children mainly learn the basic level first, after the parents help them to gain understanding of the higher levels. In an older age, children establish causal relationships between objects through explanations or the idea of cause and consequences between objects. This helps the child understand the categories and form more categories. How to understand others and ourselves?The naïve psychology focuses on the level of intellect needed to understand other people and themselves. To understand human behavior, three concepts are used: desire, beliefs and actions. There are three remarkable features of these concepts: First, the concepts refer to invisible mental states. Second, the concepts are linked to a cause-effect relationship and third, these concepts develop early in life. At the end of the firs, and beginning of the second year of life, babies learn to understand the following four aspects: understanding other people's intentions,self-awareness, a child understands that it is an individual, to focus joint attention on an object or situation intersubjectivity.At a later age,...