Edges and movement are very closely related. Out of the corner of our eye we sense that something moved, but we don’t know what. It might be a butterfly or an arrow or a fluttering banner, but we don’t know what until we turn our eyes toward that ‘something’. And then, silouetted against the pale blue sky we see a shape that we recognize as a horse coming over the nearby hill. We don’t know what color it is because the light is ‘not right’ but we instantly know it’s a horse and not a pig or Aunt Edna or an ox cart. It’s the shape!
And what is a shape but an irregular edge? And now we get to the heart of drawing objects: reproducing the irregular edge that makes a viewer ‘see’ a horse. Our brains are filled with millions of shapes, but they all have one thing in common: edges! This is not to say that once you recognize a shape you’ll know what the object is. That round thing may be a golf ball very near you or a basketball further away. And the hint that provides a clue — almost instantly — is the motion.
Golf balls travel incredibly fast; basketballs relatively slower. What’s interesting is that seeing that golf ball coming your way is first perceived as a motion out of the corner of your eye, and then as you turn your head, you instantly think “Golf ball’. Hopefully you duck in time.
And what about that horse coming over the hill? It’ll get here eventually.