Science is a systematic enterprise that builds and organises knowledge in the form of testable explanations and predictions about the universe. In an older and closely related meaning, "science" also refers to this body of knowledge itself, of the type that can be rationally explained and reliably applied. Ever since classical antiquity, science as a type of knowledge has been closely linked to philosophy. In the West during the early modern period the words "science" and "philosophy of nature" were sometimes used interchangeably and until the 19th century natural philosophy (which is today called "natural science") was considered a branch of philosophy.Music is an art form whose medium is sound. Its common elements are pitch (which governs melody and harmony), rhythm (and its associated concepts tempo, meter, and articulation), dynamics, and the sonic qualities of timbre and texture. In its most general form the activities describing music as an art form include the production of works of music, the criticism of music, the study of the history of music, and the aesthetic dissemination of music.