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On Alberti's "sign": vision and composition in quattrocento painting - Leon Battista Alberti's commentary 'On Painting'
Art Bulletin, The, Dec, 1997 by Jack M. Greenstein
The idea that intuition applies to vision from a single viewpoint distinguishes Alberti from Alhazen. Since Alhazen is concerned with vision in its everyday context, he allows that viewers move during certification. Alberti, however, restricts painting to only those "many surfaces comprehended by [a single] prospect" because the walls and panels on which painters work are single surfaces (I.12). Much has been written about the single viewpoint in Renaissance painting. What is important (and new) here is that Alberti regards the prospect from a single viewpoint as a composite of certified images. Among the many factors behind this insight, probably the most significant is Brunelleschi's first perspective demonstration panel. As is well known, Brunelleschi's first perspective demonstration featured a careful rendering of the Florentine Baptistery, which was viewed reflected in a mirror by looking from behind the panel through a small hole piercing the painted building at a point corresponding to the position of the painter standing before the actual building. Kemp argues that the thickness of the panel and the small size of the hole so severely restricted the field of view that the entire baptistery could not have been seen in a single glance.(135) He concludes that it was necessary to maneuver the eye while looking through the hole. If so, Brunelleschi's demonstration showed the importance of intuition - or changing the direction of the gaze - while looking from a single viewpoint.
Alberti's description of the visual pyramid as a composite of many small pyramids clarifies why he calls the rule of painting derived from intuition "composition."(136) In the Posterior Analytics (71a1-72a23), Aristotle explains that cognitive "units" of the arts and sciences are significant and believable things: things are significant when intellect apprehends what they are; things are believable when it is possible to affirm that they exist. By these criteria, the certified images of Alhazen cannot be broken down into smaller cognitive units by intuition alone. For Alhazen's certified image is an aggregate of clearly discerned points of colored light, and these points of light are not themselves existing things. Although the certified image comprehends all twenty-two visual sensibles, these sensibles are intermixed at each point and cannot be discerned separately without discrimination. Through discrimination the points and the sensibles are sorted out, the one by privation, the other by comparison. In this discriminated form, points and sensibles are possibly existing objects of thought. For this reason, Alhazen compares discrimination, not intuition, with composition. Alberti, on the other hand, accepts Pelacani's argument that the fundamental units of vision are colored magnitudes, each of which contains all the different kinds of visual qualities. Although the various sensibles are everywhere intermixed, they belong to different magnitudes. If intuition recognizes how surfaces fit together, it also necessarily apprehends the colored magnitudes as distinct surfaces (their whatness), which can be affirmed to exist. For Alberti, then, intuitive vision is compositional because it comprehends objects as aggregates of cognitive traits.
