At school the emphasis has traditionally always been on vertical thinking which is effective but incomplete. This selective type of thinking needs to be supplemented with the generative qualities of creative thinking. This is beginning to happen in some schools but even so creativity is usually treated as something desirable which is to be brought about by vague exhortation. There is no deliberate and practical procedure for bringing it about.

p. 5; Preface. - Lateral Thinking : Creativity Step by Step (1970)