  The Seventh Book continues with the kinds of study conducive to the education of the philosopher-ruler (521cff). The goal of intellectual development is knowledge of Forms, ultimately acquired through dialectic. Dialectic, however, is practiced late in life by a select few with the requisite memory and quickness of mind, after they have studied various, essentially mathematical disciplines. The winnowing process eliminates most people from ever developing the necessities for philosophical thought. The first steps (523a-525a) in the turn towards abstract thinking are occasioned by the need for the mind to settle questions arising from ordinary perception; that is, the mind of everyman is liable to be summoned to reflect upon the confused, and confusing, reports of perception. About a host of perceptual qualities, thick, thin, hard, soft, large and small, the senses report that they are the same, at least in certain perceptual circumstances. Lumped in with these properties is also number. The mind is summoned to settle what is large and what is small, and what is one.