Memory is the retention and retrieval in the human mind of past experiences. Memory involves both remembering and forgetting. Reasoning and intelligent behavior requires memory, since remembering is a prerequisite to reasoning. Also, the ability to solve problems or even to recognize that a problem exists depends on remembering.

Forgetting has many functions as well. The most important may be time orientation since memories tend to fade over time, and therefore new learning cannot occur without the loss or suppression of old patterns. Another function of forgetting is the relief from the anxiety of painful past experiences.

Many factors influence the retention of memories. Practice tends to build and maintain memory for a task or for any learned material. Practice has a cumulative effect on memory. It can lead to skillful performance on a musical instrument, the recitation of a poem, and even to reading and understanding the...