What do we know about the contents of human memory? A preliminary listing might be obtained by surveying the literature. Such a review shows, however, that we know precious little about the denizens of that natural habitat, the mind. It quickly becomes clear that in such a quest we cannot inquire about contents generally – the question must be narrowed. An image that helps to focus my ideas is the following.

I see myself as an ethologist or a population biologist. I might be Darwin arriving at the Galapagos Islands. It is not idle for a biologist/botanist freshly come to a new shore to ask what organisms live in the new environment. What organisms make permanent homes here? Which are migratory, coming and going throughout the seasons? Which use the land during the day, which during the night? How large are the populations now? Which beasts thrive? Which will be here tomorrow, and which in a hundred tomorrows? The census of the Galapagos, like the census of New York, yields data obtainable from no other source, giving us hints about how life in a complex system works and providing a basis for understanding other relationships in the world. A census of the contents of the mind might give us, as the census does for biology, some sense of the fitness of ideas for survival and the shapes that items assume before reaching stable configurations.