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

We divide painting into three parts and these divisions we have from nature herself. For inasmuch as the painter studies to represent things seen, we note in what way things themselves come under aspect [sub aspectu veniat]. First, when we look at [aspicimus] something, we see [videmus] it to be something that occupies a place. The painter indeed circumscribes the space of this place, and he will aptly name this rule of drawing the edges [ducendae fimbriae] circumscription. Next, intuiting [intuentes] we come to recognize [dignoscimus] how the many forward-facing surfaces fit together on the body [plurimae prospecti corpotis superficies inter se conveniant]; and designating [designans] these conjunctions [coniunctiones] of the surfaces in their places, the artist will rightly name [this rule] composition. Finally, looking with greater discrimination we discern [aspicientes distinctius . . . discernimus] the colors of the surfaces; in painting the representation of this thing, which receives all differentiation [differentia] from light, will appropriately be called by us reception of light.(130)

This account of vision employs a model familiar from Alhazen. Alberti's viewer first sees under aspects [aspicimus]; then recognizes by intuition [intuentes . . . dignoscimus]; and finally discerns with greater discrimination [aspicientes distinctius . . . discernimus].

Alberti's description of vision adapts Alhazen's optics to the conditions of painting. For Alhazen, seeing under aspects yields a clear perception of apparent color and direction, but only an uncertain comprehension of extent. For Alberti, it yields a comprehension of place and thus extent, but not color. This modification follows from Alberti's conviction (based on Pelacani's argument) that the visual pyramid includes extrinsic rays that measure the surface "as if with that instrument called a compass." Inasmuch as seeing under aspects comprehends relative direction, the viewer sees the extent as "something that occupies a place." Alberti's decision to link color perception with discriminative vision will be discussed below.

Alberti's treatment of intuition follows from his account of seeing under aspects. In Alhazen, intuitive vision ascertains visual form by sweeping the centric ray over the many surfaces of an object. The resulting certified image comprehends, albeit in composite form, all twenty-two sensible properties by which objects are known by sight. At the outset, Alberti associates composition with recognizing how surfaces fit together on a body. Since this recognition enables painters to designate the edges and arrises of surfaces, it certifies, so to speak, their circumscribable form. However, intuitive vision, he explains (II.35, 36, 38, and elsewhere), involves far more than this. Proper composition takes account of place, size, function, appearance (species), color, motion, beauty, grace, and "other things," including light and shade and roughness and smoothness. Alberti does not mention sweeping the centric ray. Yet this action might be implicit in his description, for he uses the word "intuiting" as a gerund to describe the optical activity that results in recognizing how the surfaces fit together.