Possibly I can explain my own procedure more easily. When I begin a sculpture I'm not always sure how it is going to end. In a way it has a relations… - David Smith

In particular, this question, to the sculptor:
If a drawing is traced, even with the greatest precision, from another drawing, you will perceive that the one is a copy. Although the differences may deviate less than half a hair, recognizable only by perceptual sensitivity, unanimously we rule the work of the intruder's hand as non-art.
But where is the line of true art—when the sculptor's process often introduces the hands of a plaster caster, the mold maker, the grinder and the polisher, and the patina applier, all these processes and foreign hands intruding deviations upon what was once the original work?

Gradually [late 1920's] the canvas became the base and the painting was a sculpture. [quote, early 1950's]

Gravitation is the only logical factor a sculptor has to contend with.