THE economic base of the American graduate school is the undergraduate college. More than half of the 35,000 men and women who receive Ph.D.’s each year expect to become teachers in the nation’s colleges. But although their main economic opportunities lie in teaching, their graduate-school training centers on research, as does their hope for a distinguished career. Graduate school is an apprenticeship, conducted under a mature scholar, for a career of research; those too easily discouraged by the difficulties of creating new knowledge or not strongly enough motivated by its excitements tend to drop out, or never enter. Graduate study is poor in immediate rewards, but rich in the hope of eventual distinction and even material comfort.