Hard, soft and lost edges

Where two values meet there is an edge, and the edge has a character. A hard edge (a crisp line between two values) says the form is sharp, near, in focus and in strong light. A soft edge (a gradual transition) says the form is turning away, or is further off, or is in diffuse light. A lost edge is where two adjacent areas have the same value, so the boundary disappears altogether, and the eye completes it. Lost edges are where a drawing breathes.

A beginner's drawing has hard edges everywhere, which is why it looks like a paper cut-out. Look at Corot's Bent Tree: the trunk is hard against the sky, soft where the foliage turns into shadow, and lost entirely where the ground shadow meets the base. One tree, three kinds of edge.

Use edges to steer the eye. Put the hardest edge at the focal point and soften everything else. Lose at least one edge on every form. In architecture, the sunlit corner of a tower against sky is hard; its shadow side against a shadowed hill should be nearly lost.