Western architecture theory has been based primarily on form, starting from the ratio between the lengths of adjacent sides of a rectangle. To design architecture that emphasizes materiality, one would work directly with substance and not be overly concerned with primary forms or their graphic notation. Paul Valery suggested that music and architecture share a special relationship because they exist in the surroundings and, unlike other arts, do not rely on representational images or words as intermediaries. A recognition of music relies on an intuitive perception of order, whereas a recognition of architecture relies on attributes that are esoteric, sophisticated, and often contradictory. Since the mid-nineteenth century, the discipline of architecture has been studied increasingly at a university level. Aptitude for architecture often is assumed from a student's previous abilities in cognate subjects such as drawing and mathematics, or from equal strengths in arts and sciences.