Mondrian's mature works embody his search for the visual expression of universal principles. He went from painting "natural reality" to "abstract reality," which more clearly conveyed the essential relationships that underlie all things. For him, linear geometry and primary color give "a far more intense expression than natural form and color." He wrote: "All things are parts of a whole. Everything is constituted by relation and reciprocity. Color exists only through another color, dimension is defined by "another" dimension. This is why I say that relation is the principal thing."