Form and space
The most striking characteristic of the forms employed by Indian sculptors is the fact that all the units of form into which the surfaces of Indian sculptures are divided are convex, and the only true concavities in the whole of Indian art are special cases. Apart from the art of Gandhara, strongly influenced from the West, concavities occur only in the treatment of the leading ideas of skeletal or demonic figures, as the eye sockets and belly of a disease goddess, and in the free- hanging parts of draperies. Nowhere else in the whole fabric of Indian sculpture are concavities treated as formal units, as they are by Donatello, Michelangelo or the artists of Gothic Europe.
The hollows on Indian sculptures are only the meeting places of convexities, and so, of course, appear as smooth linear channels. It is possible to relate this fact to Indian theories of reality. Reality to the Indian eye, is a form, like a pot or fruit, that gives evidence of its content of space by its convexly curved surface. The expression of a visual form is dependent on its containing space. In this way, Indian sculptures define and limit their own space; they do not fit into an already existent space continuum in which they can move freely. The system of relationships used to compose the work depends upon this.
Plastic forms used by Indian sculptors, no less than their figure types, are very general and not very much differentiated. Volume and solidity, the general effect of rounded mass, are emphasized. Crystalline faceting is used only to express the horrible and unattractive. The linear elements that appear as sinuous contours or drapery folds are themselves subordinated to general pattern- types. Deeply curved and sinuous outlines, by the method called 'development', are converted into spatial statements. The line always sets out on a regularly curving or undulating course, spatially 'complete' as it were before it starts, keeping close to the general pattern. Thus the time- element of line, is subordinated to a closed spatial idea. This is a kind of visual expression of the familiar Indian concept of time as a series of ever- recurring cycles. One specially beautiful use of the sinuous and undulant patterned line in Indian sculpture appears in some of the landscape and vegetation designs on shrines of all ages.
The meaning of an Indian work of art depends upon reading this characteristic approach to form.  Upon it depends the method by which single figures make a total self-contained continuity.  They are built up out of volumes whose deeply rounded sections are intelligible from the main viewpoint and change smoothly and continuously. The exterior lines and channels, defining the eyes or the wrinkles on the belly, for example, appear then, as if one experiences them from inside the skin of the sculpture, as rhythmic punctuations in the contained plastic continuum. This is why Indian sculpture can be understood from inside the stone.
To the critical Western eye this absence of concavities and, most of all, the absence of a multitude of inflexions in the outer surface (which our eye persuades us are important attributes of 'reality') are disturbing, and prevent many people coming to terms with Indian art. The Westerner is accustomed to stand outside, over against a sculpture, and treat it as a separate entity which he assesses critically from outside. His view of space and reality demands that the external space-continuum in which both he and his sculpture exist shall be allowed to impinge inwards, into the main masses of sculptural form.  These are hollows that punctuate the humps, where he is accustomed in a real object to see shadows.  To the critical eye of a medieval Indian sculptor Western art would appear to be appallingly lacking in the interior unity.
To the Indian sculptor, linear articulation of changing and varied, but simple, volumes demands that both sides of the volume be clearly intelligible in relation to each other. The Indian could not accept the view of, say, the volume of a calf-muscle offered by much European art, where only part of a contour is visible, and the rest is lost in a hollow that does not allow its other contours to be defined.
This consideration, taken together with the fact already mentioned that Indian sculpture is fundamentally relief sculpture, accounts for another of its characteristics. This is the absence of any crossings or complications of contour on the figures, and the great stress laid on the recessions of the side surfaces. Indeed, much of the force of some of the greatest Indian sculpture from the earliest times has been the result of careful exaggeration of the depth of the continuous recessions of side surfaces spanning the distance from the edge of the frontal plane to the bounding contour at the back.   In order to preserve its plastic effect it is continuous. The result, on the spectator, of this emphasis on the depth of purely convex forms is a tremendous impression of plastic force.  This visual force would have been totally dissipated if the sculptor had been obliged, as Western sculptors have been, to consider a number of other viewpoints from either side and behind.
So most Indian sculpture has been made to produce an over-ridingly powerful impression from a single viewpoint. Striking examples of this are the figures of musicians on the upper stage of the Surya temple at Konarak, and the sculptures of the Elephanta cave temple.
Again, because of the adherence of Indian sculpture to a background ground, the conceptualization of the empty, negative spaces between figures and parts of figures became an important compositional feature. These negative spaces themselves are often as carefully formulated into sequences of clearly articulated closed and simple forms as are the solids. The aesthetic effect of many of the greatest works of Indian art depends upon the intimate mating together of solid form and negative space, each carried, as it were, to its highest formal power.