In this booklet all facets of lines and shapes are discussed. They are always qualified by Kropholler; he considers one line or form clearly more suitable for application in architecture than another. Beauty plays a major role here. All the forms described are illustrated by existing buildings (Classical temples, Romanesque, Gothic, St. Peter's, Berlage, De Bazel, but also Egyptian, Islamic, Chinese and Indian architecture) in which these lines and forms were applied in an ideal and, according to Kropholler, the only correct way. Kropholler also gives examples here and there in the text of how not to do it (modernism and Amsterdam School).