Field maple leaves with cast shadows

Burgess Field, 26 June 2010.

Shadows are negative in being holes in light (and may as in the self-shadows of the second picture burn holes in positives - here too the negative spaces and the self-shadows are similar in form, or rather inverses). But shadows are also like imprints in casting shapes. Plato in the Republic says of images that they are "in the first place, shadows, and in the second place, reflections in water and in solid, smooth and polished bodies and the like."
Shadows lose more information about the object producing them than reflected light, and in this they are eloquent reminders of the dimness of our perception. Any image is just that, an image, and a shadow. (Plato's Cave.)

Cast shadows are, of course, the Origin of Painting:

It was through his daughter that he [Butades] made the discovery; who, being deeply in love with a young man about to depart on a long journey, traced the profile of his face, as thrown upon the wall by the light of the lamp. Upon seeing this, her father filled in the outline, by compressing clay upon the surface, and so made a face in relief, which he then hardened by fire along with other articles of pottery.
-- Pliny, Natural History (c. 77-79 CE), Book XXXV.

In the eighteenth century there was both a vogue for silhouettes (so-named along with other cheaply produced objects á la Silhouette in times of austerity under the brief spell of Etienne de Silhouette as French finance minister in 1759) and for the theme of Dibutades (the Corinthian Maid) in such paintings as David Allan, Origin of Painting (1775), Joseph Wright of Derby, The Corinthian Maid (1782-1784), Joseph-Benoît Suvée, Dibutades, or the Origin of Drawing (1791), and Jean-Baptiste Regnault, The Origin of Painting: Dibutades Tracing the Portrait of a Shepherd (1785).

The role of shadows in the perception of shape, and their relation to light and space, are the subject of Michael Baxandall's Shadows and Enlightenment (Yale University Press, 1995), as well as the problem of how to paint them (for which also see Ernst Gombrich, Shadows: the depiction of cast shadows in Western art, (Yale University Press, 1995).