The Music of the Spheres tradition, the idea of the universe as a musical structure, along with the concept of the Great Chain of Being, has been a major component of Western thought from its earliest glimmerings until the scientific revolution of the seventeenth and eighteenth centuries, when this concept finally disappeared from the mainstream of our culture. ;It is an extremely ancient tradition, coming from, among others, Egyptian, Babylonian, Sumerian, Jewish, and Indian sources, later filtering through to the ancient Greeks via the mythological figure of Orpheus and the semimythological figure of Pythagoras. This theme is clearly expressed in the writings of Plato, specifically the cosmogony of the Timaeus, and the vision of the universe described in The Myth of Er at the end of The Republic . An analysis of both these sources reveals multiple layers of symbolism, from Pythagorean number theory to mythological archetypes. ;Within these texts and elsewhere in his writings, Plato outlines an ontology and an epistemology that are essential to the understanding of his musical cosmology. Rejected by Aristotle, misunderstood by many subsequent writers, revived by others, these doctrines became muddled and distorted until, by the seventeenth century, an enormously subtle idea had been reduced to a statement of mere physical fact that does not hold up under empirical examination. Consequently, it has been banished from the mainstream of thought and occupies a tenuous position in the realm of the occult. ;Now, however, the realization is growing that various dimensions of knowledge have been jettisoned in the search for empirical certainty. One of the victims has been a comprehensive understanding of music, which continues to elude theorists to this day. The core components of Plato's musical cosmology, in the form of a world-view that incorporates consciousness as well as matter, is essential for the correct understanding of music as well as many other phenomena, particularly in the humanities and the social sciences