Leonardo da Vinci had a thing or two to say to his contemporaries about their confusion between creative designing and drawing skills [Da Vinci 1956, fols. 61v-62r]:
“You who compose subject pictures, do not articulate the individual parts of those pictures with determinate outlines, or else there will happen to you what usually happens to many and different painters who want every, even the slightest trace of charcoal to remain valid; this sort of person may well earn a fortune but no praise with his art, for it frequently happens that the creature represented fails to move its limbs in accordance with the movements of the mind… So, painters, rough out the arrangement of the limbs of your fingers and first attend to the movements appropriate to the mental state of the creatures that make up your picture rather than to the beauty and perfection of their parts.”
Leonardo had used a simple but effective technique for working out compositions which deviated radically from the prevalent method then of the “unfailing line which needed no correction and no second thoughts”. The novelty of his method involves working literally on top of schematic sketches, using them as frame of reference to develop more detailed versions and variations (see figure).
Leonardo’s method can be considered the forerunner of the use of the tracing paper, now common among artists and designers to explore design alternatives by sketching on superimposed layers of translucent media. The tracing paper is both transparent enough for the preceding sketches to show through as guidelines or framework, but at the same time opaque enough to uphold the overlaid sketch.
This is perceptual emergence in practice (see also my blog on Emergent Subshapes). If indeed emergent thinking is the key to creativity, the tracing paper is the prime creative designing tool; not the drawing board, modeling (in all media), CAD (and all current computer graphics ‘special effects’), nor even the sketchbook per se.