This dissertation examines pre-Kantian rational philosophy and the development of the discipline of aesthetics in the North German Enlightenment. With emphasis on the historical conception of the physiological and psychological experience of music, this project determines the function of music both privately and socially in the eighteenth century. As a result, I identify the era of rational aesthetics (ca.1750-1800) as a music-historical period unified by the aesthetic function and metaphysical experience of music, which inform the underlying motivation for musical styles, genres, and means of expression, leading to a more meaningful and compelling historical periodization. The philosophy of Alexander Baumgarten, Johann Georg Sulzer, and others enable definitions of the experience of beautiful objects and those concepts related to music composition, listening, and taste, and determine how rational aesthetics impacted the practice, function, and ultimately the prevailing style of music in the era. The construction, style, and performance means of the free fantasia, the most personal and expressive genre of the era, identify its function as the private act of solitude, or a musical meditation. An examination of pleasure societies establishes the role of music in performance and discussion in both social gatherings and learned musical clubs for conveying the morally …