Positive - Contour - Negative. A positive is always a figure: the representation of a three dimensional object (by convexity - concavity, light- shadow, color, etc.). A contour is one-dimensional: it is a line, border between figure and ground (its enviroment). The negative is the complement of a figure: it is everything that is not the figure. Its role is only to define the figure, so the negative part ("no-figure") need no differentation: it is two-dimensional plane (sometimes just a black area sorrounding the figure).