 John G. Harries considered a common ground in the ideas that underlie developments in 20th-century art such as Serial art, Systems Art, Constructivism and Kinetic art.These kind of arts often do not stem directly from observations of things visible in the external natural environment, but from the observation of depicted shapes and of the relationship between them.Systems art, according to Harries, represents a deliberate attempt by artists to develop a more flexible frame of reference.