On Alberti's "sign": vision and composition in quattrocento painting - Leon Battista Alberti's commentary 'On Painting'

Alberti's association of color with discriminative vision rather than seeing under aspects follows directly from his equation of the visible in painting with signs. For Alhazen and Bacon, signs are visible qualities that promote recognition of objects or their properties. Recognition of objects by signs results in immediate identification without intuition; recognition of properties by signs serves intuition, which builds up knowledge of things by certifying the forms (or, more properly, intentions) of their surfaces. In Albertian painting, proper composition insures that all the surfaces and members of a body "should agree in species" (specie omnia conveniant; II.37). As previously shown, both Alhazen and Aquinas maintain that the "species" of things seen are stored in memory as universal forms or phantasms, where they constitute a person's knowledge of what makes things what they are. Alhazen further explains that these universal forms are conglomerates of visible qualities, built up through repeated acts of observation. Alberti recommends that painters study the appearances of bodies in nature and fix the things that they have learned deeply in memory (II.36). In this way, he explains, they understand how to accommodate members to one another in size, function, and appearance. These repeated acts of observation build up a memory of universal forms and thereby constitute the painter's knowledge of what makes things what they are. Accordingly, when the surfaces and members are properly composed, the species of the depicted things are immediately recognizable by prior cognition.

Yet because painters are concerned only with what "is received by visual contemplation [intuitium]," Alberti discusses only signs for visual properties.(142) He reduces this concept of the sign to a simple, clear formula. "In this place," he writes, "I call a sign anything that is in a surface so that it can be beheld by the eye" (I.2). For Alberti, any visual quality that makes a surface recognizable as "the outer part of a body . . . not by depth, but by width and length and in like manner by its qualities" (I.2) is a sign.(143)

Although his definition of a sign as anything beheld "in a surface" might seem to apply to marks, figures, or brushwork on the picture plane, Alberti never refers to the pictorial works or their material elements as signs. Instead, in a famous passage comparing painting to an intersection or transparent plane, he calls on painters to subordinate the visual qualities of the crafted object - what Aquinas calls the "certain thing" - to the visual properties of the depicted bodies. He writes (I.12):

When they [painters] go around a surface with lines and then fill the described places with colors, nothing is to be sought more than that on this one surface are represented many forms of surfaces, and not otherwise than if this surface, which they work on with colors, were wholly transparent and so glasslike [admodum vitrea et perlucida huiusmodi] that the entire visual pyramid passed through it. . . .