The ability not just to think, but to think well is, or at the very least should be, essential to fulfilled adult life. We might wish to ask, then, whether the thinking abilities of average people are sufficiently developed to make a maximum contribution to people's life fulfillment. Our ability to answer this question, it turns out, is severely limited. Human mental ability has been the subject of systematic empirical study for the past century, beginning with early psychometric investigations that provided the foundation for the theory and practice of the measurement of intelligence and culminating in the now-mature and well-respected field of modern cognitive psychology. Although much has been learned, there is still a good deal of human thinking about which we know almost nothing – thinking that might figure importantly in people's lives once they have completed formal schooling, and the particular intellectual demands it poses, and begin to channel their energies into the concerns of adult life.

Only very recently have researchers begun to examine the sorts of thinking that occur in people's everyday lives, in contrast to the kinds of thinking elicited on intelligence tests or in psychological laboratories or the kinds emphasized in school. Thus far, such efforts have focused largely on the thinking that people do in their work lives (Perlmutter et al., 1990; Scribner, 1986; Sternberg & Wagner, 1986; Wagner & Sternberg, 1985, 1986).