SOMETIMES you might feel that if yo

SOMETIMES you might feel that if you had a perfect memory, all your problems with learning things would be solved. You would be able to sail through exams without much revision - and would never again face the embarrassment of forgetting someone's name.

But imagine, for a moment, not forgetting anything - not even last year's shopping lists. You would be overloaded with information.

With hard work you can recall the parts of a verb or the layout of a town as you need them - so that you can learn a foreign language or gain a taxi-driver's licence. But the memory feats called for by some professions and by exams are only one of the roles memory plays in our lives.

Memory, the faculty by which we recall things or keep them in the mind, covers a wide range of actions and needs. What we know about the brain is far from complete, so philosophers and scientists find it difficult to be precise about the nature of memory.

But the question "how do we remember?" is not a purely scientific one about brain functioning, or merely a philosophical one about knowledge. Historians remind us that the way people remember changes over time.

Anthropologists (who study and compare societies and customs) also help us answer the question. They argue that some kinds of memory cannot be written down, and are therefore neglected. These memories held in common are often referred to as "social memory" or "collective memory".

Remembering and forgetting can be understood in many different ways, but broadly, three distinct classes of memory have been established: personal, cognitive and habit memory.