Music played an important role in the drama, but we must admit that this role is not very clear. We know that the chorus had vocal functions; it prefaced scenes and accompanied them. In the tragedy its original number, twlve, was later increased to fifteen, while in the comedy its number rose to twenty-four. We also know that the individual actors broke into song and that the aulos played during the action, thereby lending to the play a melodramatic touch (in the ancient, not the modern, sense). The aulos was the only and exclusive instrument of the theater; it was never employed except singly, and it was never exchanged for the lyre.
It is the nature of the simplest and oldest form of drama that, at the height of intensity of feeling and excitement, it turns into music, because music is able to continue to express emotions when the deeply stirred soul of man can utter only inarticulate aries. Sophocles was a dramatist; his strength lies in the conduct of a plot, an action. But Aeschylus, a musician, a choral lyricist, creates works prompted by a mood of profound innter excitement, the mood of a composer, one which procedes articulate poetic ideas. To communicate this mood successfully he must appeal to the emotional responsivess of the public, and the means he uses to this end are of a lyrico-musical nature. In the days of Aeschylus, music and lyricism still formed an indivisible entity, and word and tone, poem and melody were created simultaneously.
Correspondencesand proportions, which play so important a role in music, can be expressed in numbers. To the Greek mind music was part of a mathematical philosophy which the Pythagoreans, the precursors of Russell, Eddington, and Einstein, held to represent the whole of philosophy. Or to put it differently, we may say that the mathematical theory of harmony was part of a general theory of the harmony of the cosmos. The disciples of Pythagoras, as well as the non-Pythagorean authors, agree in attributing the discovery of the numeric laws of harmony to the great philosopher, and they are unanimous in their praise of the importance of this discovery.