A sculptor has to be an expert on the articulation of an object: its joints, its axes. He observes how this swivels, how that bends and folds. His figure may actually be rather stiff but everywhere it will give the impression that it can move. The folds of drapery may coil at a joint like a spring; one arm may lift while the other seems to be about to fall; the head may be turned right while the eyes look left, as if about to pull the head after.
There are traditional poses which the ancients found suggestive: an imbalance in the shoulders and hips reminding one of a scales temporarily loaded on one side. Another way is to prepare the ground in front of an object or limb that might move—lay out the track by clearing away folds, for instance. Let the eye imagine how it would move or fall, how easy it would be to do so.
In a portrait one hand of the sitter might clutch the arm of his chair while the other relaxes. Since our eye, which seeks to balance, naturally compares the two hands, each of them can be imagined doing or just about to do what the other is doing.
There are shapes that suggest movement. A circle and a ball seem to roll, especially if there is a course in front of them and some room to move. There are shapes that look unstable, ready to change, to collapse, to topple. This look of tension in things is the heart of life-likeness. All great figures since the Greeks are conceived in this way, to make the onlooker imagine more than there is.
In any figure this movement is important but in sculpture it is….more so. I was going to say that it is the sine qua non, but then I remembered the great statues of Egyptian art, which have little articulation or none, no movement. In early sculpture, where figures are really idols, the aim was to portray timelessness, majesty. Movement is the stuff of life, not of eternity; nor is tension compatible with dignity.