Since the beginning of bluegrass music, there have been almost two different branches (traditional bluegrass genre and radical bluegrass genre), which have gradually developed and changed over the past 60 years.
Traditional bluegrass music, as its name suggests, emphasizes traditional elements in the music. Traditional bluegrass musicians use only acoustic instruments to perform folk songs and simple traditional harmonious songs. Early traditional bluegrass also used some instruments that were not accepted by mainstream bluegrass, such as washboard, mouthharp and harmonica; at the same time, the use of bluegrass instruments was sometimes slightly different (some bands had multiple guitarists and violinist). The genre's music has simple melodies and lyrics, often using the I-IV-V chord pattern, and the guitarist rarely takes the lead (a notable difference from gospel songs).
Radical bluegrass music attracted widespread attention from the late 1960s to the 1970s, as some bands began to play with electroacoustic instruments and introduced songs from other genres (especially rock & roll). However, the emergence of radical bluegrass can be traced back to the first bluegrass band. Get a feel for Earl Scruggs' early banjo and bass duo with the Foggy Mountain Boys, which reveals some traces of radical bluegrass. The four key elements of the genre are instruments (including electroacoustic instruments), songs that imitate or borrow styles from other genres, modified harmonies, and "jamband" style improvisation.