Definitions:

Adaptation: adapting to the world through assimilation and accommodation.

Assimilation: The process by which a person takes material into their mind from the environment, which may mean changing the evidence of their senses to make it fit.

Accommodation: The difference made to one's mind or concepts by the process of assimilation. (Note that assimilation and accommodation go together: you can't have one without the other.)

Classification: The ability to group objects together on the basis of common features.

Class inclusion: The understanding, more advanced than simple classification, that some classes or sets of objects are also sub-sets of a larger class. (E.g. there is a class of objects called dogs. There is also a class called animals. But all dogs are also animals, so the class of animals includes that of dogs)

Conservation: The realization that objects or sets of objects stay the same even when they are changed about or made to look different.

Decentration: The ability to move away from one system of classification to another one as appropriate.

Egocentrism: The belief that you are the centre of the universe and everything revolves around you: the corresponding inability to see the world as someone else does and adapt to it. Not moral "selfishness", just an early stage of psychological development.

Operation: The process of working something out in your head. Young children (in the sensorimotor and pre-operational stages) have to act, and try things out in the real world, to work things out (like count on fingers): older children and adults can do more in their heads.

Schema (scheme): The representation in the mind of a set of perceptions, ideas, and/or actions, which go together.

Stage: A period in a child's development in which he or she is capable of understanding some things but not others

Syncretism: the child tends to merge diverse elements into one unarticulated image in perception, in thinking and in acting, on the basis of some chance impression.

Autistic thought: (Vygotsky) is a late development, a result of realistic thought and of its corollary, thinking in concepts, which leads to a degree of autonomy from reality and thus permits satisfaction in fantasy of the needs frustrated in life (day dreaming).

The pleasure principle states that people seek pleasure and avoid pain, i.e., people see to satisfy biological and psychological needs.

The reality principle defers gratification when necessary.

Spontaneous concepts: the child is not conscious of them because his attention is always centered on the object to which the concept refers, never on the act of thought itself. It is nonconscious and nonsystematic.

Nonspontaneous concepts: concepts are consciously taught and acquired.

The zone of proximal development is the difference between what a learner can do without help and what he or she can do with help.