This book is concerned with this further or prior claim about valid curricular subjects-the claim that they represent knowledge of what is true-from which the practical or therapeutic uses seen in the two above examples are derived. It will be my object in this chapter and in Chapter 3 to elucidate my claim with reference to two particular and very influential attempts to draw distinctions between what can and cannot be known and to use this distinction as an instrument for curricular selection. Both accounts make the claim that the justification of the inclusion of a subject in the curriculum is that it constitutes knowledge or, at very least, that it must assist men in reaching a state of mind in which knowledge can be acquired and the world interpreted.[4] In this chapter I propose taking the first of these accounts, namely that of Plato, who attempts to determine what can be known and who draws up his results in the form of criteria that will determine what subjects ought to be included and what excluded from the curriculum. In Chapter 3 I propose analysing a modern theory of knowledge and the curriculum, namely that of Hirst, which has a similar objective, while attempting to avoid the pitfalls into which Plato's argument seems to fall. But if readers think that so ancient a writer need not concern someone entering the teaching profession today, I do not suggest that they skip the following pages, since in them I shall show how the ghost of Plato haunts many a curriculum-planning session to this day.