Classical music generally refers to the formal musical tradition of the Western world, considered to be distinct from Western folk music or popular music traditions. It is sometimes distinguished as Western classical music, as the term "classical music" may also refer to non-Western traditions which exhibit similar formal qualities. In addition to formality, classical music is often characterized by complexity in its musical form and harmonic organization, particularly with the use of polyphony. Since at least the 9th-century it has been primarily a written tradition, spawning a sophisticated notational system, as well as accompanying literature in analytical, critical, historiographical, musicological and philosophical practices. A foundational component of Western Culture, classical music is frequently seen from the perspective of individual or groups of composers, whose compositions, personalities and beliefs have fundamentally shaped its history.