What is a dynamic memory? It is a flexible, open-ended system. Compare the way an expert stores knowledge about books in his field to the way a library catalog system does the same job. In a library, an initial set of categories is chosen to describe a domain of knowledge. Within those categories, titles, authors, and subjects of the books are recorded. Such a system is not dynamic. Eventually, the categories will have to be changed; overutilized categories will require updating; other categories will have to be created to handle new subjects and subject divisions.

A library does not have a dynamic memory. It changes with great difficulty. More important, to change it requires outside intervention. An expert has neither of these problems. He can change his internal classification system easily when his interests change, or when his knowledge of a particular subject matter changes. For the most part, these changes are not conscious. The expert may relate one idea to another or he may fail to do so. He knows when he knows something, but there is a lot he doesn't know he knows. He may be able to categorize without knowing the categorization scheme he uses. He can make observations about what he knows and thus can alter the memory structures that catalog what he knows. He can do this without even realizing he has done it. He has a dynamic memory.