Myron is the first sculptor who appears to have enlarged the scope of realism, having more rhythms [rhythmos] in his art than Polycleitus and being more careful in his proportions [symmetria]. Yet he himself so far as surface configuration goes attained great finish, but he does not seem to have given expression to the feelings of the mind, and moreover he has not treated the hair and the pubes with any more accuracy than had been achieved by the rude work of olden days. (Pliny the Elder)The term rhythmos derives from the dance, long an integral part of Greek community culture. It is easy to find our word rhythm there, but probably a mistake to rely on it too firmly. The rhythms of Myron's Discobolos, as we can see, emerge from the way its parts and shapes echo each other throughout the whole. The Greek concept of rhythmos is not the same thing. It refers to the momentary positions taken by dancers during the course of their performance. By striving to find some equivalent of rhythmos in their work, sculptors were seeking to establish a mechanism whereby the world of flux might be represented in their art. In this way, they provide a way for rational inquiry itself - the proportions and patterns of their craft - to explore the nature of motion.
Symmetria is generally linked to rhythmos as a particular effect much sought after by Greek sculptors. Symmetria derives from the notion that the parts of a work will be proportionate to each other and, hence, to the whole. Here we pose, and are posed, questions of design and proportion in things generally, but particularly in things like buildings and pieces of sculpture. In architecture, symmetria takes account of the such things as the relations among ground plans and elevations, and between column diameter and columniation - so that a proportional relation exists between how wide the columns are and the distance between each column.
As such, symmetriais present in the work of both the Geometric and the Archaic periods as well as the Classical. It is perhaps best known, however, as the goal for which Polykleitos was striving in, for example, his Doryphoros, where harmonious proportion of the whole combines with rhythmos.
Polykleitos was remembered in Antiquity as the chief master and foremost exponent of the principle of symmetria, ‘commensurability of parts,’ in art. Around the middle of the fifth century, or shortly thereafter, he wrote a treatise, known as the Canon, in which he delineated and apparently sought to justify the system of symmetria which he had developed for representing the human body in sculpture. The Canon seems to have been well-known and influential, in its intent at least, in later times...
The basic idea behind the symmetria principle, that an artistic composition should consist of clearly definable parts, was a venerable one in Greek art. It existed, as we have seen, in the Geometric period and continued in force throughout the Archaic period. Greek sculpture in particular in the Archaic period saw the development of workshop formulae of symmetria which seem to have been inspired by Egyptian prototypes, but underwent considerable local development.
What distinguished Polykleitos’ system of symmetria from what had gone on before, however, was that it seems to have had philosophical content as well as a practical function. Its aim was to express what Polykleitos himself called [in Greek] to eu, ‘the perfect’ or ‘the good,’ and what others seems to have called to kallos, ‘the beautiful.’ There is some evidence that the philosophical tradition which gave rise to and helped to shape this philosophical conception of symmetria was Pythagoreanism” (Pollitt, 106).