Rodin is considered the father of modern sculpture. He returned to the ancient concerns of the thrusts and solidity of sculptural masses.  The play of abstract geometric masses in opposition to each other gives his sculpture power, vitality, dynamic complexity and a feeling of solid existence that is very pleasing to look at. “The sculptural problems he set for himself had to do, as did Michelangelo before him, with the composition or containment, the definition and resolution of the thrust and tension of forms, the expansion and contraction of space and the dynamic interplay of the two.” (Sculpture of the Twentieth Century, Andrew Carnduff Ritchie) For example the pyramidal shapes formed by the striding legs and uplifted arm of St John the Baptist Preaching ,are given added force and complexity by the spiral movement described by the right arm, pointing spatially to the left foot ,and extending through the head and the left arm.
A similar composition can be seen in Walking Man. (This sculpture can be seen in the foyer of the Smith College Museum of Art.) The inverted triangular mass of the upper torso is given forward thrust by its forward curve as well as the athletic stride of the lower body which simultaneously provides stability because it is a pyramidal shape.
“First I made closer studies after nature, like The Bronze Age. Later I understood that art required more breadth - exaggeration, in fact, and my aim was then, after the Burghers of Calais, to find ways of exaggerating logically – that is to say, by reasonable amplification of the modeling. That also consists in the constant reduction…to a geometrical figure, and the resolve to sacrifice every part to the synthesis of its aspect. Look what they did in Gothic times. Take the Cathedral of Chartes as an example: one of its towers is massive and without ornamentation, having been neglected in order that the exquisite delicacy of the other could be better seen. In sculpture the projection of the sheaths of muscles must be accentuated the shortenings heightened, the holes made deeper. Sculpture is the art of the hole and the lump, not the straightness of smooth faces without modeling. The ignorant say: “That is not finished,” but there is no notion more false than this of finish, unless it be that of “elegance.”  People would kill art with these two ideas. It is by work carried to its extremity not in the sense of finish or the copying of details, but in the justness of the successive planes, that one obtains solidity and life. The public which has been perverted by the academical prejudices, confounds art with neatness or spruceness. Molding from nature is copying of the most exact kind, and yet it has neither movement or eloquence. Art steps in to exaggerate certain planes and give fineness to others. In sculpture everything depends on the way modeling is carried out, and the active line of the plane found, the hollows and projections rendered, and their connections. That is how one obtains fine lights and beautiful shadows that are not opaque. All this is a matter personal to the tact and temperament of each sculptor, and that is why it is not a transmissible method or studio recipe, but a just law. I see it in Michelangelo and in the ancients.

 “All through the Renaissance,” according to Herbert Read in The Art of Sculpture, “the development of sculpture may be interpreted as a struggle between the plastic and the painterly, between the palpable and the visible, between integral mass and the perspectival complex. The painterly conception of sculpture won the day: mass was dissolved in fluid atmosphere…” The movement toward realistic rendering of form and a painterly concept of sculpture that emphasized surface over palpable mass was given authority by the French Academy. Rodin opposed the academical approach and returned the concerns of sculpture to depth and mass.

“Art is the sensuous apprehension or plastic cognition of the world:” continues Read, “its purpose is to increase our sense of the wholeness of being, to develop our consciousness of reality. In that sense it becomes part of our conception of evolutionary purpose, and there is a spiritual as well as a physical joy in the experience of such a conquest. Great works of art, said Rodin, ‘express, indeed, all that genius feels in the presence of Nature; they represent Nature with all the clearness, with all the magnificence which a human being can discover in her; but they also fling themselves against that immense Unknown which everywhere envelops our little world of the known. For, after all, we only feel and conceive those things which are patent to us and which impress our minds and our senses. But all the rest is plunged in infinite obscurity. Even a thousand things which should be clear to us are hidden because we are not organized to see them.’ The function of art, Rodin went on to say, is not only to tell us all that can be known but to make us aware that there is a limit to what is known. Great works of art bring us to the edge of this abyss, and, make us feel a little dizzy….It is a question of gamut, of possible range of sensational apprehension and expressive power. There is, in the full scale of plastic sensibility, a power attaching to ponderability and mass, to the gestated and palpable volume of a solid creation, that cannot be experienced in any other manner, by any other means than sculpture.”