Memory stores information in a system that consists of three categories. It is important to understand these three categories of memory because they determine planning and organisation in the brain. All three areas of memory must be in harmony with each other in order to work as a coordinated whole.

Semantic memory stores knowledge about rules, logic, historical events and maths. Semantic memory can be seen as a kind of encyclopaedia of abstract and definitional knowledge. Here, for example, the brain stores traffic rules, mathematical formulae or the names of important politicians in history.

Episodic memory stores information relating to sensory perceptions or feelings from one's own experience. The memory is usually evoked in the form of visual images and the storage is based on the strength of the feelings experienced. The stronger the sensation, the more vivid the memory. For example, everyone remembers the first painful fall from a bicycle, while later, less painful falls are forgotten.
Episodic memory is the part that is inhibited when people consciously try to forget painful experiences.

Although semantic and episodic memory are different memory systems, they are both referred to as declarative. This means that both are accessible through conscious thought. People can consciously say whether a memory exists or not.

A far more complex memory system is the behavioural memory (procedural memory). The information is largely stored subconsciously and involves learning processes. An early example of behavioural memory is learning to walk. Hardly anyone can prove what needs to be done to be able to walk upright. Although everyone has a basic understanding of balance, the complex movement of walking is stored in a different part of the memory, which only retrieves the information subconsciously.