CS-5 is the fifth part of the Kurt Schwitters System (KSS). It is a theoretical architecture and design system based on the principles of Gestalt psychology, which Schwitters developed from 1921 onwards. It includes basic principles of design like symmetry, rhythm, pattern and balance. It defines elements that can be arranged according to the Gestalt principles to create structured, harmonious and meaningful images. The elements are generalized visual forms, combinations of geometric shapes, letters, lines and grids, which can be combined to create a composition. These forms can also be seen as visual metaphors that illustrate ideas and concepts. As an example of the application of CS-5, Schwitters developed a series of abstract posters he called Merz postcards as an example of his aesthetic.