We are, in many respects, what we remember. But how much do we do? So
far, science has provided only a very partial answer to this riddle. T
he magical number seven, plus or minus two, seems to constrain the cap
acity of our immediate memory (Miller 1956). But surely its constraint
s dissipate when memories settle in long-term stores. Yet how big are
these stores? If we combine all of our factual knowledge and personal
reminiscence, childhood scenes and memories of the past day, intimate
experiences and professional expertise-how many items are there, that,
combined together, mold us into unique individuals? The answer is not
simple, and neither is the question. For example, what is an item in
long-term memory? And how can we measure it, being sure that we unveil
memory capacity and not merely the occasional ability to tap it? Such
theoretical and practical difficulties, no doubt, have contributed to
the fact that the capacity of human memory is still an enigma. Yet, d
espite the inherent and undeniable complexities, the issue deserves to
be retrieved, once in a while, from the oblivions of the collective m
emory of the scientific community. (For a selection of earlier discuss
ions of the size of human long-term memory, see Galton 1879; Landauer
1986; Crovitz et al. 1991.)