Shadow is the obstruction of light. Shadows appear to me to be of supreme importance in perspective, because, without them opaque and solid bodies will be ill defined; that which is contained within their outlines and their boundaries themselves will be ill-understood unless they are shown against a background of a different tone from themselves.

What It Means

This is a placeholder explanation generated by the low-overhead model. It interprets "Shadow is the obstruction of light. Shadows appear to me to be of supreme importance in perspective, because, without them opaque and solid bodies will be ill defined; that which is contained within their outlines and their boundaries themselves will be ill-understood unless they are shown against a background of a different tone from themselves." in the context of "Leonardo da Vinci in: Sean Cubitt The Practice of Light: A Genealogy of Visual Technologies from Prints to Pixels, MIT Press, 5 September 2014, p. 171" to mean that wisdom is timeless.