Line

In the Elements of Geometry, Euclid defines the line as “a length without breadth,” an element without width and depth. The concept of line occurs in propositions, both theorems and proofs, given the postulates that it is possible to draw a straight line between any two points and to extend continuously any line. In Euclid’s Optics, lines are the subject of theorems. Rubin studied the perceptual conditions that could have given an intuitive contribution to the definition of geometrical objects that like in Euclid’s geometry do not occur in experience, yet have a relation with visual constructions. Pictures exploit markings endowed with perceptual linearity and continuity which realize lines. To convey meaning, namely to enable observers seeing the shape of pictured objects, lines obey a grammar that rules their type and combination. Moreover, lines stand for discontinuities that allow observers to sample the structure of the environment.