1. Guillaume Durand [William Durandus], The Rationale divinorum officiorum of William Durand of Mende: A New Translation of the Prologue and Book One, trans. Timothy M. Thibodeau (New York: Columbia University Press, 2007), 34.
2. Bonaventura, Meditations on the Life of Christ; An Illustrated Manuscript of the Fourteenth Century, trans. Isa Ragusa and Rosalie B. Green (Princeton, N.J.: Princeton University Press, 1961), 330.
3. Anonymous, Zardino de Oration, quoted in Michael Baxandall, Painting and Experience in Fifteenth-century Italy: A Primer in the Social History of Pictorial Style (Oxford: Clarendon Press, 1972), 46.
4. Leon Battista Alberti, On Painting, trans. and intro. John R. Spencer (New Haven and London: Yale University Press, 1956; rev. ed. 1966), 77.
5. Leonardo da Vinci, The Literary Works of Leonardo da Vinci, trans. and comp. Jean Paul Richter, 2 vols. (3rd ed., London: Phaidon, 1970), 1: 338.