Without the knowledge of perspective, constructive drawing is impossible. Leonardo Da Vinci called it the "bridle and rudder of painting." Every form, from a grain of sand to a mountain, exists in perspective. It is the first thing a student must learn. Like the alphabet in a language, without it, one would not be able to write. Too many students by-pass this phase of learning. The knowledge of perspective makes it possible to create the illusion that objects and figures are three dimensional on a two dimensional surface such as a sheet of paper, canvas or wall.