Around the middle of the eighteenth century the leading figures of the French Enlightenment engaged in a philosophical debate about the nature of music. The principal participants - Rousseau, Diderot, and d'Alembert - were responding to the views of the composer-theorist Jean-Philippe Rameau, who was both a participant and increasingly a subject of controversy. The discussion centred upon three different events occurring roughly simultaneously. The first was Rameau's formulation of the principle of the fundamental bass - a principle which explained the structure of chords and their progression. The second was the writing of the Encyclopedie, edited by Diderot and d'Alembert with articles on music by Rousseau. The third was the 'Querelle des Bouffons', over the relative merits of Italian comic opera and French tragic opera. The philosophes, in the typical manner of Enlightenment thinkers, were able to move freely from the broad issues of philosophy and criticism, to the more technical questions of music theory, considering music as both art and science. Their dialogue was one of extraordinary depth and richness and dealt with some of the most fundamental issues of the French Enlightenment. This book traces the development of the ideas discussed and reveals the vigour with which they were debated. It reconstructs the link between music theory and criticism that has been lost over time. It also presents extensive passages from the debate in English translation for the first time. In explaining fully the various aesthetic, philosophical, scientific, as well as musical issues involved, it will be of relevance to Enlightenment scholars of many disciplines.