A Treatise on Painting, by Leonardo da Vinci
Senex and Taylor, London
The first things you are to consider in a Painting, are, whether the Figures have a Relievo answerable to the place wherein they are found, and to the Light which they receive, and whether the Shadows are not the same in the Extremes, and in the Middles of Groups; it being one thing to be incompassed on every side with Shadows, and another to be barely shadow'd on a single side. Now a Figure in the middle of a Group, is under the first of these circumstances, being hemm'd in with dark Bodies on every Hand; Whereas another in the extreme, is shared between the Shadow diffused from the Group, and the Light it receives from its Luminary.
Observe secondly. whether by the Ordonnance or Disposition of the Figure, they appear accommodated to the Subject; and well suited to the History which they are intended to represent.
And thirdly, whether the Figures be attentive to the business, and to the occasion of their being there; and whether their Attitudes, and Expression, be suitable to the matter in hand.