Musicologists have sometimes classified music according to a trichotomic distinction such as Philip Tagg's "axiomatic triangle consisting of 'folk', 'art' and 'popular' musics". He explains that each of these three is distinguishable from the others according to certain criteria.
The term art music refers primarily to classical traditions, including both contemporary and historical classical music forms. Art music exists in many parts of the world. It emphasizes formal styles that invite technical and detailed deconstruction and criticism, and demand focused attention from the listener. In western practice, art music is considered primarily a written musical tradition, preserved in some form of music notation rather than being transmitted orally, by rote, or in recordings, as popular and traditional music usually are. Historically, most western art music has been written down using the standard forms of music notation that evolved in Europe, beginning well before the Renaissance and reaching its maturity in the Romantic period. The identity of a "work" or "piece" of art music is usually defined by the notated version rather than by a particular performance. This is so particularly in the case of western classical music. Art music may include certain forms of jazz, though some feel that jazz is primarily a form of popular music.
The term popular music refers to any musical style accessible to the general public and disseminated by the mass media. Musicologist and popular music specialist Philip Tagg defined the notion in the light of sociocultural and economical aspects:
"Popular music, unlike art music, is (1) conceived for mass distribution to large and often socioculturally heterogeneous groups of listeners, (2) stored and distributed in non-written form, (3) only possible in an industrial monetary economy where it becomes a commodity and (4) in capitalist societies, subject to the laws of 'free' enterprise ... it should ideally sell as much as possible."
Popular music is found on most commercial radio stations, in most commercial music retailers and department stores, and in movie and television soundtracks. It is noted on the Billboard charts and, in addition to singer-songwriters and composers, it involves music producers more than other genres do.
The distinction between classical and popular music has sometimes been blurred in marginal areas such as minimalist music and light classics. In this respect music is like fiction, which likewise draws a distinction between classics and popular fiction that is not always precise.
Traditional music is a modern name for what has been called "folk music", excluding the expansion of the term folk music to include much non-traditional material. The defining characteristics of traditional music are:
Oral transmission: The music is handed down and learned through singing, listening, and sometimes dancing;
Cultural basis: The music derives from and is part of the traditions of a particular region or culture.
A fusion genre is a music genre that combines two or more genres. For example, rock and roll originally developed as a fusion of blues, gospel music and country music. The main characteristics of fusion genres are variations in tempo, rhythm, and style.